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techspecial
07-25-2011, 10:40 PM
Hi all...I've been pretty silent because all has been well until recently.
The year before last I upgraded to the Blueprint small block engine Model MBP3550CT which is basically a 350 .040 over with some fancy sounding parts. For exhaust i went with the Stainless Marine manifolds with the pretty stainless elbows. I don't have straight throughs though I have the rare S tubes that moves exhaust discharge to the water line.
First year no problems ran really good...no serious issues.
Second year (after warranty experatation) I started to experience a gradual decrease in WOT RPM's...Then it started to run like I dropped a cylinder. Diagnosis proved that I had wiped a couple of lobes on the relatively mild cam.
Replaced the cam and lifters (flat tappet hydraulic) and it seemed to run OK but I couldn't keep water out of my crankcase...Not a lot...Just enough to milk up the oil. Reset the intake manifold...Still H2O in oil...Pulled off the heads and saw that both gaskets had issues and there was evidence of water in the back four cylinders, And it gets worse...Two broken pistons have pieces broken off between the outer top edge and the first set of rings. Numbers 5 and 6 are the damaged cans...Is this a classic reversion issue? The cam is not really radical and I checked with a couple of guys on the board and they assured me that I'd be OK. Are these Keith Black Hyperuetectic (?) pistons available with the apparently pedigreed rings available. This really sucks...I've been battling with this thing since August and I'm just about out of money and patience...Any suggestions would be greatly appreciated. Thanks,Mike

Dr. David Fleming
07-25-2011, 11:37 PM
A marine cam is unlike any other engine camshaft because the exhaust valve must be shut at top dead center to prevent water from being taken in on the intake stroke.

In automotive engines the intake and exhaust valves are open at the same time in what is called "valve overlap." In this overlap situation the exhaust remains open past top dead center and the intake is open early before the intake stroke. This allows the intake valve to be fully open while the exhaust is exiting under pressure. In this automotive type engineering, the exhaust can pull some intake charge into the exhaust system and the cylinder which results in more power because the cylinders are more fully filled with the fuel air mix.

Marine engines are engineered differently because of their proximity to water. Some manifolds and pipes barely above the waterline when the boat is not running. Water is also sprayed into the manifold not too far past the exhaust valves to cool the exhaust gasses for muffling and fire protection.

If you are not using a bonafined Marine Cam you are very likely pulling water into the cylinders from the wet exhaust. This is called "reversion." "Injestion" is when sinking or a wave or other rocking of the boat back fills the engine from the sea.

A bunch of guys saying a cam is "ok" is no way to qualify a cam. Who are the guys what is their marine experience? Crane Cams profile for say the 500EFI racing engine show the exhaust valve fully closed at TDC. This is no automotive engine cam.

Tyler Crockett and other marine engine builders are using dry exhaust systems and getting away with automotive racing cams. This means the water is not sprayed into the exhaust gas to cool it. They use a water jacketed exhaust that dumps water overboard separate from the exhaust system - the exhaust gas is loud and hot and usually well above the waterline.

mrfixxall
07-26-2011, 01:24 AM
were do you have the timing set at?

Offset
07-26-2011, 08:20 AM
Dr. David thanks for the lesson on marine camshafts. I was aware of this problem but not really clear on the exact cause. Makes sense now with your explanation.

Thank you, this place is a rolling history and technical lesson. Wish I had more to contribute.:thumbsup:

techspecial
07-26-2011, 08:44 AM
I had the ignition (Thunderbolt IV) replaced by my local marine mechanic...
I believe he said his final timing was 38 degrees total...
The stock ignition module didn't match the new motor.

MOP
07-26-2011, 01:11 PM
38! Not on a bet for marine fine for street, to much unless everything is at absolute perfection very hard to achieve with today's available fuel. Why was the IV not a match for your engine? I run a pretty expensive stroker motor and use the stock IV as do many it is very reliable, all I did was add a hot coil. I think your mechanic handed you a bill of goods!

GeneD
07-26-2011, 01:13 PM
First off...those KB Hypereutectic pistons are total bullsh*t.
I broke the top of my pistons in the same way you're describing. The factory won't warrantee them. They'll tell you that the top ring was inproperly gapped. I did this 3 times before I met my present machinist who after describing to him what was happening, pulled a piston out of a box and said, "Is this what your piston looks like?" And yeah...the breaks were identical.
Nothing will beat a good set of forged pistons, and the way we run our boats, we need 'em.
Another thing they will tell you is that your spark timing is off. And if what the guy is telling you is true...there might be some truth to it.
Check this out...
http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF
Marine cams do have a special cam timing/lobe spacing to prevent reversion. I forget what the spec is, but look at the marine cam specs from say, Crane, or one of the other manufacturers. You will see the difference.
Finally, not much can beat the Thunderbolt IV or V for exacting spark timing and spark voltage. It's one of the best marine applications out there.
I had a client with the marine MSD and he had nothing but trouble with it, though the factory was really nice about things, he ended up getting rid of it and going with the Thunderbolt and never had a spark problem again.
Sorry about your motor...

MOP
07-26-2011, 01:40 PM
Added not the stock Merc recommendations are for stock setups, in our lighter boat and looking for better performance you can go higher. I have gone as high a 34 with good fuel, I found only a little above the 30 that I normally run. High ignition settings are spooky unless everything is spot on, in my opinion should not be used for every day running. Thinking about your cam, did you break it in in the recommended manner? Flat tappet cam should be broken in at about 2500 RPM for 15 minutes, you cannot get away with babying a flat tappet. Also it is highly recommenced that you run motorcycle oil which has a higher zinc content, zinc has been removed from automotive oils giving flat tappet cams a much shorter life span. Automotive oil is just fine for roller setups, but due to the loads on our engines roller or not only the best oils should be used. Many think our boats engine are much like our car engine, that could not be farther from the truth. Take the time to do decent research before you put it back together and use a knowledgeable marine mechanic, they know what even good car mechanics do not!

mrfixxall
07-26-2011, 02:40 PM
ok 38* is too too muxh,,next ? who's cylinder heads? vortech's ?

BUIZILLA
07-26-2011, 02:49 PM
you should stick to 30-32* total timing on fast burn or Vortec heads

a 22* module and 10* initial should be plenty

olredalert
07-26-2011, 08:27 PM
-----"Brad Penn" oil (google it) for break-in oil. Made specifically for new flat-tappet cam motors. Have broken in several new cams with no problem......Bill S

mrfixxall
07-26-2011, 08:57 PM
you should stick to 30-32* total timing on fast burn or Vortec heads

a 22* module and 10* initial should be plenty


+1,,you beat me to the punch line :wink:

maddad
07-26-2011, 10:01 PM
A marine cam is unlike any other engine camshaft because the exhaust valve must be shut at top dead center to prevent water from being taken in on the intake stroke.
Hi Dr. D, your posts are always filled with a bunch of info, but just so bad info isn't passed on I've got to say this is not true. Unless you mean the top of the compresion stroke when everything is closed. ALL four stroke motors run some degree of overlap, how much there is says a lot about how much power you will make, how much you can get away with without reversion has a lot to do with the exhaust style and the engines internal sizes, mostly how much valve is feeding how much cylinder.

techspecial
07-27-2011, 02:37 PM
I think I may be dealing with two separate issues here...
I'm blaming the wiped cam lobes on the factory break in procedure.
Rotella-T (high ZDDP content) then switch to synthetic (low ZDDP content).
The manufacturer changed their recommendation and now warns of low ZDDP oil. It just seems strange that I beat the thing pretty good the first year and had no issues.
As for the pistons...I'm thinking reversion with bad timing setting...
My marine mechanic said he had to "power time" it. I don't know what that means but it doesn't sound good.

The plan is to install high quality forged pistons and weld tails on the risers to divert the water as far back as I can. Timing will be set (by me) to the Blueprint specifications. Although I never experienced any temperature spikes I did notice a less than adequate impeller on my Alpha One water pump too...

My plan is subject to change if you all think I'm doing something stupid...
THANKS FOR ALL THE RESPONSES!!! Mike

mrfixxall
07-27-2011, 02:58 PM
extending the tips wont do anything with out seperating the water from the exhaust all the way through the s pipe to the tips..what is the correct cam spec's? just trying to save you from doing all the extra work that is not needed..

techspecial
07-27-2011, 03:04 PM
I'll get the specs to you ASAP...Thanks!!!

techspecial
07-27-2011, 05:03 PM
Here's what I have:

Comp Cams 12-240-4
"Xtreme Marine"

Lift: .480/.489
Duration: 270/286
RPM 1600-5800

Thanks In Advance!!!

mrfixxall
07-27-2011, 05:33 PM
Here's what I have:

Comp Cams 12-240-4
"Xtreme Marine"

Lift: .480/.489
Duration: 270/286
RPM 1600-5800

Thanks In Advance!!!


thats the same cam im using..you will have no troubles with reversion..if your only spinning your engine to 5200 rpm's i would advance it 2-4* just to be sure..

im using emi manifords and i put the cam in @ *110 on the icl, my motor pulls hard to 5800 and will exceed that rpm to 6200 on a long stretch..keep in mind that im only running a 355 with aluminun heads that have been ported and flowed along with some other mods..

techspecial
07-27-2011, 05:56 PM
Are you thinking that it's timing that did me in?

CHACHI
07-28-2011, 07:12 AM
Are you thinking that it's timing that did me in?
and wiped cams.

Ken

CHACHI
07-28-2011, 07:18 AM
I think I may be dealing with two separate issues here...
I'm blaming the wiped cam lobes on the factory break in procedure.
Rotella-T (high ZDDP content) then switch to synthetic (low ZDDP content).
The manufacturer changed their recommendation and now warns of low ZDDP oil. It just seems strange that I beat the thing pretty good the first year and had no issues.


How do you know the Rotella-T is a high zinc oil and the synthetic a low zinc.

All the oil manufactures have lowered the PPM (parts per million) of anti-wear (zinc and phosphous) in their oils.

Here is a report of Rotella from four years back. I can assure you Shell hasn't added more anti-wear since then.

Ken

GeneD
07-28-2011, 08:48 AM
Well, obviously the motor has to be broken down and re-done.
Unless the pistons show signs of detonation, I wouldn't think reversion would be an issue.
I believe the broken pistons are from bad piston design. I know lots of guys running these things in their cars with no ill effects. I experienced problems, and knew for sure the ring gap was correct, and I always de-tune the ignition timing to 6 degrees BDC. I have to run 93 Octane due to the high compression ratio.
The wiped cam can not be diagnosed without knowing some things. I've installed lots of cams in my life. The only one I had a problem with was when I installed a Blue Racer cam in my Corvette. I wiped out 3 of 'em. Finally, knowing I did proper break-in, I changed out the high RPM valve springs I had in there, with the proper L-82 springs the car came with and never again had a problem.
I know lots of guys run over 5000 RPM with their boats. I feel this is a bit dangerous in many ways. But the first is that most Mercruiser stuff is only rated to 5000 RPM's. Even the HP500's and 550's only go to 5250 via limit chip.
Often times it's not the HP that will kill a drive, it's the RPM's. I know all about broken drive shafts and propshafts using high performance motors, but I think most of those failures are from abuse. Hitting the throttle way hard on take off, and fast deccelleration. During my racing days, these failures were normally the result of bad throttling during re-entry after launching the boat on a big wave. This would often result in broken propellers too.
The cam manufacturer you're using is a good one, I wouldn't be against using them again.
But the cam you're talking about is made for a jet boat with type A impeller. Most of the jet boats I've seen have dry exhaust. I wonder if this caused a problem with you. Also, the curve would be off for your application. I'm thinking a better choice would be the Comp cam 12-210-2, or possibly the 12-324-4...a cam I've always wanted to try.
Buy some nice forged pistons so you'll never have to worry about that ever again. Check the springs in the head, did they use high performance springs?
Maybe consider using Competition Cam's recommendation?
I'm told that there are only 2 manufacturers of flat tappet lifters. So just get a normal set of those, it will be just fine.
Get a set of nice marine head gaskets.
And for goodness sakes put the Thunderbolt ignition back on there. What was it you said, the old ignition module didn't fit the engine set-up? Do you change distributer with vacuum or mechanical advance? Where did this new module come from?
If you look closely at that spark timing chart, the curve doesn't change all that dramatically for any of the engines. I believe the curve is matched to marine application torque.
And staying out of the 5000 RPM range will add longevity that engine more than anything. I know the torque curve might say something different, but my old boss (the propeller people) always said that it's the top of the HP curve that you want to tune your propeller to, not the Torque curve. And the way to tune the engine RPM is to start adding pitch to your propeller until you're at the RPM you want to be at, and that RPM is at the top of the HP curve.
Speed is made in propellers via pitch. The larger the pitch your motor can handle, the faster you will go.
The oil is a consideration, no doubt about it. But again, I've used normal everyday oil in motors with new lifters with no ill effects. The added zinc in certain oils will also add a bit of anti-corrosive to the crankcase, something to think about considering you now have water in the oil.
You have a lot to think about. I think if you're willing, you can do this job for cheap by yourself, with a little help from your local machinist as you'll have to swap rods on the pistons.
Good luck...keep us posted.

techspecial
07-28-2011, 03:08 PM
Gene,
Thank you very much for the very detailed reply!
I'll try to reiterate my situation...
My 23P prop limits my RPM to 4700. I've never overreved.
I have Stainless Exhaust manifolds with their wet risers/elbows.
My local mechanic replaced my original 1986 TB IV ignition module with a smaller unit that I think is still a TB IV but a newer vintage...He says he couldn't get my original unit to work which I think means it wouldn't screw up my timing enough for him. I've installed a new cam and lifter set identical to the original. I was running Mobil 1 20/50 which I understand has the lowest ZDDP concentration of their line. The reason I broke the thing in with Rotella T is because it is what Blueprint Engines requires according to their warranty requirements. I've intentionally taken the boat airborne at times but I'm not crazy and I've always been careful during re-entry ( I don't drink anymore and I always have my wife with me...She's my human rev limiter). I will go with forged pistons this time for sure...The cylinder bores look good considering...One is clean and the other has visible marks that don't hang up on a fingernail. The cylinders will be honed and the pistons and rings will be replaced. What is your recommendation as far as pistons go?
The heads will be checked & magnafluxed. As far as springs go I'm clueless.
Thanks Again!!! Mike

mattyboy
08-08-2011, 08:40 AM
Tech, sorry to hear about your issues hope you get them squared away.


on a side note here someone is going to have to explain the relation of overlap and reversion in a marine motor to me.

I've looked at my setup and trying to figure out where this water would be that the Dr. says will be sucked in on the intake stroke?

pipnit
08-08-2011, 09:34 AM
Bummer Tech, hopefully you get her up and running soon.




As an aside, I like to run this stuff in my boat: https://www.sierramadrecollection.com/store/secure/images/products/18713.png

silverghost
08-08-2011, 03:58 PM
Tech, sorry to hear about your issues hope you get them squared away.


on a side note here someone is going to have to explain the relation of overlap and reversion in a marine motor to me.

I've looked at my setup and trying to figure out where this water would be that the Dr. says will be sucked in on the intake stroke?

Matty~
Valve overlap happens when the intake valve opens while the exhaust valve is still open on the same cylinder.
Overlap is the period of time when both intake & exhaust valves are still both open at the very same time on an exhaust then intake stroke.
The cylinder piston on it's intake stroke then pulls some wet exhaust water back into this cylinder through this still open exhaust valve..
Thus the exhaust water "Reverts" back into the now open & charging cylinder.
And~~ we all know that water will not compress ~ so an engine failure disaster soon results.
In a high performance auto application high cam overlap actually helps clear out more spent exhaust gases & thus increases horsepower.
However in a wet exhaust marine engine it can be a real dangrous disaster that can severely damage & wreck the engine.
High overlap cams do not belong on a wet exhaust marine engine.

mattyboy
08-08-2011, 05:38 PM
please explain how the exhaust is wet??? is it a leak? looking at my setup I am having a problem seeing where the water would come from.

joseph m. hahnl
08-08-2011, 06:09 PM
I think I may be dealing with two separate issues here...
I'm blaming the wiped cam lobes on the factory break in procedure.
Rotella-T (high ZDDP content) then switch to synthetic (low ZDDP content).
The manufacturer changed their recommendation and now warns of low ZDDP oil. It just seems strange that I beat the thing pretty good the first year and had no issues.
As for the pistons...I'm thinking reversion with bad timing setting...
My marine mechanic said he had to "power time" it. I don't know what that means but it doesn't sound good.

The plan is to install high quality forged pistons and weld tails on the risers to divert the water as far back as I can. Timing will be set (by me) to the Blueprint specifications. Although I never experienced any temperature spikes I did notice a less than adequate impeller on my Alpha One water pump too...

My plan is subject to change if you all think I'm doing something stupid...
THANKS FOR ALL THE RESPONSES!!! Mike

The problem with the cam shaft lobes, is flat tappets. If you notice none of any modern high performance marine engines that are produced by mercury are flat tappet. They are all roller tappets/lifters. I would suspect as marine engines evolved and increase rpm and horse power the flat tappet was proved to fail and was eliminated. In this link to Mercury remanufactured engines . The flat tappets cams and lifters are thrown away. Roller cams are reground and roller lifters are rebuilt. I think that in itself says a lot about using flat tappets versus roller


http://www.mercurymarine.com/repower/mercruiser/remanufactured-mercruiser-products/

mrfixxall
08-08-2011, 06:34 PM
The problem with the cam shaft lobes, is flat tappets. If you notice none of any modern high performance marine engines that are produced by mercury are flat tappet. They are all roller tappets/lifters. I would suspect as marine engines evolved and increase rpm and horse power the flat tappet was proved to fail and was eliminated. In this link to Mercury remanufactured engines . The flat tappets cams and lifters are thrown away. Roller cams are reground and roller lifters are rebuilt. I think that in itself says a lot about using flat tappets versus roller


http://www.mercurymarine.com/repower/mercruiser/remanufactured-mercruiser-products/


the merc 600 sc's are flat tappet...

mattyboy
08-10-2011, 10:12 AM
I am having a probleming seeing and understanding wet exhaust water????

I have looked and tested my setup with center risers and if there are no leaks the water and gas mix and the end of the riser . In order for water to be sucked in it would need to be sucked up the gas chamber 4-5 inches then fall down into one of the four tubes then travel up and inch or so to come to rest ontop of the exhaust valve. the riser is solid cast iron for about 3 inches and is angled up where it meets the exhaust port on the head. The main part of the riser is filled with water but the bottom part is not. I would imagine a good reason why the bottom tubes are angled and tucked up , their hot and you would really need to reach down then up in order to touch them. I would imagine the tubes are hot enough that small amounts of water would evaporate if they wound up there.


I understand that ingestion happens, I understand that HP is about flow in and out and big flow in needs big flow out. so is the problem in the exhaust systems geared towards high performance?? or where the system mixes the water and gas?

I mean if you have had water forced up your exhaust pipe thru the risers and onto the exhaust valves I think you have a problem no matter what cam you have.

I must be missing something do marine heads mix or inject water into the exhaust gases before the risers???

okay I know this is going get out of hand but I have to say it anyway
so one cyl is sucking seems there should be one blowing too so how does the water get past that??

so what am I missing?

hdsadey
08-10-2011, 01:08 PM
Has anyone ever considered idle rpms for this problem as well? I just had a thought that if your cam is on the borderline of having to much overlap that too low of an idle would increase the problem? Low rpm allowing the engine to lope more would give water more opportunity to be ingested? Negative pressures being created in the exhaust system? Does this make sense or am I way off base?

mattyboy
08-11-2011, 06:59 AM
OK so I found the missing part to the puzzle "RESONANCE".

Reversion is an incomplete term as it is the ends not the means. RESONANCE REVERSION is what is happening. This is what is giving the water in the exhaust system the ability to walk back up thru the system

Looks like it was known early in the 60's and addressed then as usual new designers pay no attention to history and leave out important design features.

so how many of you have vacuum breaks in your risers??

http://www.michel-christen.com/ExhaustElbows.pdf

mattyboy
08-11-2011, 08:21 AM
like to hear what everyone thinks, that report was about marine engines mainly merc stock marine engines with marine cams and stock exhausts??

so anyone have crosssections of aftermarket exhausts? which ones have vacuum breaks?

maddad
08-11-2011, 09:31 AM
That's a great link matty. The risers on my stainless marine exhaust have no vacuum break, but add the water much farther from and lower than the drop back into the exhaust port area. I would like to read how that extra distance affects how the water acts in there.

joseph m. hahnl
08-11-2011, 09:10 PM
I have the old style that is no longer available. I thought they where 4 inch though.The rubber hose is 4". One of The main reasons why I don't want to put the boat in salt water is, because that elbow is no longer made. I don't think I need to worry about it at the moment as nothing is modified . But it's defiantly something that should be examined with after market exhausts and when re caming. Great find Matty, something as simple as an engineer who doesn't know what he's doing. that's a little hard to believe

http://1.bp.blogspot.com/_Xkv5o55jDiI/TMBaejV7ToI/AAAAAAAAAjo/1govm5ymG6I/s320/Don't+believe+me+-+101.jpg

CHACHI
08-12-2011, 06:57 AM
Everybody is talking overlap and duration causing reversion, doesn't lobe seperation angle come into play with this?

Ken

BUIZILLA
08-12-2011, 07:36 AM
Everybody is talking overlap and duration causing reversion, doesn't lobe seperation angle come into play with this?

Ken yup.... :lookaroun:

mattyboy
08-12-2011, 08:11 AM
overlap,duration,seperation all fall victim to resonance.
the problem is not how long , how far the problem is water being where it shouldn't be. I do guess how long and how far can make the result of the problem little or big. but again the report was directed at stock marine engines designed by the mfg'r to work in the marine environment, not modified high performance with modified cams and aftermarket exhausts.

was going to remove my external flappers and just go with the internal for a cleaner look scratch that idea. sorta glad that my tips are another foot or so higher than a 16,18 or 22.

ok so who knows how to shutoff their motor at just the right time so all the exhaust valve are closed??????????

CHACHI
08-12-2011, 11:56 AM
yup.... :lookaroun:

Thanks Jim, I thought I was overthinking it.

Ken

maddad
08-12-2011, 01:42 PM
ok so who knows how to shutoff their motor at just the right time so all the exhaust valve are closed??????????

Matty, that's not possible. Every 90* of crank rotation(in a V-8)an exhaust valve begins it's 4-stroke cycle. A mild 270* duration cam has 3 exhaust valves in some stage of open at all times.

mattyboy
08-12-2011, 01:51 PM
Mike,

I was kidding there I knew that wasn't possible. sorry should have used a smiley

Ghost
08-12-2011, 08:39 PM
OK so I found the missing part to the puzzle "RESONANCE".

Reversion is an incomplete term as it is the ends not the means. RESONANCE REVERSION is what is happening. This is what is giving the water in the exhaust system the ability to walk back up thru the system

Looks like it was known early in the 60's and addressed then as usual new designers pay no attention to history and leave out important design features.

so how many of you have vacuum breaks in your risers??

http://www.michel-christen.com/ExhaustElbows.pdf

This is on my list of the 10 most useful posts ever. Highly recommend folks crack open the PDF and read it. REALLY good stuff, thanks for posting it!

hdsadey
08-16-2011, 09:07 AM
Ok so I read the whole deal on reversion. Wondering if I'm gonna have the same problem with the IMCO risers that I have. They don't seem to have that hook in there. Can modify them if need be before installing them. What do you all think.

MOP
08-16-2011, 10:27 AM
Turbulators are used by a few header makers, they do away with the issue. Gil was the first to introduce them. Merc now has them in the later style gaskets, I am on the road but will post more info and pic's later.

Ghost
08-16-2011, 11:08 AM
Thanks Phil, I'm eager to learn more about the turbulators. One difference I see between them and the hooks in the riser castings (from the study Matty posted) is the turbulator flange is at the joint between manifold and riser, where the exhaust flow is straight up and any reversion flow would be straight down.

If the only issue is breaking up the resonance somewhere in the system, then I suppose turbulators could work just fine and be completely effective.

But the hooks in the castings from the study were on the riser DOWNSLOPE, such that the exhaust was moving downward, and any water that was marching back toward the engine would be on its way up a hill. And, the hooks were on the bottom side of the riser tube, not all the way around it. Leading one to wonder if their effectiveness was as a break to the resonance, as a dam to the water marching back up the riser, or both.

If the "dam" aspect has any importance under any conditions, the turbulator will almost certainly fail to handle those conditions. Because the water marching backwards through the turbulator system will have passed the crest inside the riser and gotten into the vertical tube above the manifold, and will be falling down to the manifold. So, water that has gotten close to the turbulator has the potential to accumulate until enough is there for it to burp back down into the manifold, a bit like Coke burping out of a full bottle that has been turned upside down with the lid off.

Whereas in the cast riser hook situation, that water is stuck trying to march uphill gets blocked and robbed of the vacuum pulling it in BEFORE it reaches the top of the hill, and will just naturally fall down the slope of the riser toward the exhaust port in the transom. The more water accumulates, the more gravity wants it to just run back down the aft riser slope and out.

Somehow, my gut tells me the closeer that the hook/break is toward the motor (and thus the farther the hook/break is from where the water and exhaust mix at the end of the riser), the less effective it might be.

But this is all purely my speculation. I'd love to hear what anyone really knows about this one.

MOP
08-16-2011, 01:06 PM
Check post#4 it has a diagram of the Gil/Merc setup, the turbulator is between the gaskets made of stainless with an up turned lip. Fix goes into a little detail on them, also I have read about guys removing them and not gaining any power so they only help!

Dr. David Fleming
08-20-2011, 06:59 PM
Merc 500 the racing engine before the 500EFI - this engine used a Holley Carb and cast Gill exhaust manifolds - serious reversion issues developed, enough to cause warrenty problems for Merc. Eventually they went to the turbulator inserts in the exhaust manifold pipe to hold off the water reversion. When they came out with the Merc 500EFI the following year - with the Arizona Speed and Marine fuel injection system bought by Merc - and CMI stainless steel four tube headers - this engine had little of the reversion that the Gill setup did. Basic watchword on the Merc 500 was not to remove the turbulators.

techspecial
06-23-2012, 11:27 PM
Well the motor has been rebuilt (if you can call it that)...
New block...Was already 40 over so I replaced it with a "seasoned" block that's now 30 over.
New forged pistons...Crank, con rods, cam, lifters, and pushrods were good...
Rocker studs had to be replaced because they looked like they were installed with channel locks.
One head had to be replaced..Found a plug weld so it had to go.
New valves and springs.
EVERYTHING MACHINED!!!
Boy what an ordeal!! We have a local machine shop here that has a very good reputation so they got the job.
This week I'll replace my gimbal bearing and lower unit water pump and hopefully get the engine back in.
I'll try my old original Tbolt IV and see if I can get the timing at about 30 degrees total.
I'll break in the cam according to directions with Brad Penn break in oil when I get that far.
I'm only running it on the hose for a short time to make sure I have good cooling flow through the flappers, then
it goes in the water. I have flappers at the water line so it's hard to judge coolant flow in the water.

Is there any way to install a water pressure sensor to check coolant flow?

Is there anything that I'm missing? I really don't want to go through this again!!!

Thanks for all of your help!!! Mike

pipnit
06-25-2012, 07:30 AM
I now have a water pressure guage but last season, I got a fitting for one of the plugs on the intake manifold and used some tubing and a sump pump guage to check PSI. I had added a new stainless marine water intake and had to "tune" it. Now the guage just gives me piece of mind.

CHACHI
06-25-2012, 07:56 AM
72010