Compression Check on my Magnum

[Bigbroadjumper]

I wanted to check the overall health of my Magnum engines. I did a compression check on the starboard engine. It's a SBC LT1 with Dart 202 heads and board I believe .060 over. I think the numbers look good but I would like some professional opinions. Here's how they look.

Cold engine, coil disconnected, WOT, all plugs in except the one for testing.

#1) 150 lbs
#2) 150 lbs
#3) 140 lbs
#4) 150 lbs
#5) 150 lbs
#6) 150 lbs
#7) 160 lbs
#8) 150 lbs

Do these numbers look right?

Thanks

Off to do the other engine. What a PITA trying to get between these motors. Thank god they are not big blocks!

[Carl C]

IMO, very good readings.

[Eugene Nahemow]

Shouldn't these number ideally be 175-190.

[Bigbroadjumper]

That's what I'm wondering? The compression on the stock Chris Craft engine was 150 but these are bumped up. They also have a slightly larger cam. About 700 hours on the rebuild. They run well just wondering if it's getting close to new power?

[Carl C]

Shouldn't these number ideally be 175-190.

Engine was cold. With warm engine readings would no doubt be higher. Consistency is just as important and you have that.

[Carl C]

"Bigger" cam can also lower readings. Those numbers are good. Where's Fixxall?

[BUIZILLA]

throttle WO when cranking?

cam bleeds off some cranking pressure so I would say leave_it _alone

[Bigbroadjumper]

Thanks to everyone for the response.

[Bigbroadjumper]

I finally got around to doing my Port engine. Numbers are a little different

1) 150
2) 160
3) 140
4) 170
5) 160
6) 160
7) 170
8) 170

On the # 3 it sounds like air is leaking someplace.?

[MOP]

When you hear air the valves are the first suspect, probably time to do the heads.

[Carl C]

Retest with engine warm. Then do a leak-down test.

[Eugene Nahemow]

That's what I'm wondering? The compression on the stock Chris Craft engine was 150 but these are bumped up. They also have a slightly larger cam. About 700 hours on the rebuild. They run well just wondering if it's getting close to new power?

700 Hours? I would say it's time to do a little freshning.

[lars]

Wish You the best with the engines Bob. I got the feeling You got infatuated

with the Marauder for a while and who can blame You. I'm wishing for new

photos of the Maltese running of course. I'm sure that she's easily my

favorite Maltese by far and I hope You were able to run her a little the last few seasons. How did the re-wiring go and what else have You done since 2008? Keep Us fans up to speed.

Warm regards, Lars.

[Bigbroadjumper]

Thanks for the kind words Lars,
The rewiring went pretty well, I want to redo all the gauges this winter and then I might pull all the wiring out. I'm also thinking of replacing the head liner. Mine is still the blue shag carpet from 1974 "very shagadellic" but showing her age. I redid the bolsters and rear seat. But did not use the candy stripe... that in my mind is a mistake. Soon it will be back to the original look.

[mphatc]

A bit late to this thread . . . sorry . .

Compression tests should be done with all spark plugs removed, throttle held wide open and a battery charger to maintain a constant battery voltage though all the cranking . . this ensure that your piston speeds will be equal on the 1st cylinder and the last . .

On a carbed engine, always open the throttle once, and find a way to hold it open. You don't want to pump gasoline in with the accelerator pump, it washes down the cylinderwalls and will take away the seal of the rings.
Lastly, never forget to short out the secondary coil lead to the distributor.

I suggest a complete retest . . on warm engines.
Mario L.

[Bigbroadjumper]

Thanks again to all who gave their input. I will warm them up and get my son to climb around the engines. My tired old body is not in the mood to do it again.:cool:

[Eugene Nahemow]

Thanks again to all who gave their input. I will warm them up and get my son to climb around the engines. My tired old body is not in the mood to do it again.:cool:

I remember the days of my chest being black and blue after a weekend of work on the Magnums engines. Finding tools or parts that I dropped into the bilge was the highlight of my day.

[Bigbroadjumper]

LOL, I have a long stick with double sided tape to retrieve items from the bilge.

[mphatc]

Ahhhh . . .

I know the feeling . ., little access, deep bilge,

I'll share a hurt with you guys . .

This past weekend I wanted to repair the hindge on the engine hatch . . .note that a 68 Magnum hatch is 4' x 5 1/2' and solid 3/4 plywood coverd on both sides by f-glass . . . .
and they have no hatch lift or built in supports . . so mine was propped up by a boat hook . . .

While standing behind the boat, my left hand was pulling the bottom rear corner of the hatch towards the hinge, in my right was the large straight slot screw driver. I pulled hard enough to release the boat hook, and as the hatch decided to close I was not quick enough to pull my hand out of the way . . .:eek::eek::eek::nilly::nilly::mad::mad:

Fortunately the boat hook fell in such a way that the hatch didn't close . . .all the way . . but enough so that my ring finger and little finger are still numb and w/o any feeling. Never in the last 40 years have I felt pain like this!!! I recall a good hard injury when I was 15 . . :frown:

I'm a lucky guy, someone was close by and could lift the hatch, and it didn't take off my fingers which would have happened had the boat hook fallen clear out of the way.

be careful guys!

Mario

[Marlin275]

Ahhhh . . .

Fortunately the boat hook fell in such a way that the hatch didn't close . . .all the way . . but enough so that my ring finger and little finger are still numb and w/o any feeling. Never in the last 40 years have I felt pain like this!!! I recall a good hard injury when I was 15 . . :frown:


It hurts just to read that . . .

[Ghost]

It hurts just to read that . . .


Agreed. I ripped a bicep tendon putting new impellers in (sounded just like ripping a tshirt BTW).

Reading this made it hurt a lot less by comparison...

[Bigbroadjumper]

I have the spring thing that holds my hatch up....I've bumped it several times and had the hatch fall on my fat head! The ringing lasts longer then the pain. I hope you're ok!

[mphatc]

My fingers survived, feeling is 80% back and improving . . how's the compression after another test . . ??

Read my post on my 350s with low compression in the Time Flies thread, maybe it will help.
http://www.donzi.net/forums/showthread.php?p=575299#post575299

Mario L.