Compression Confusion....

[EricG]

Well, I spent all day replacing all of the tune up parts on the Z21 looking for my Cut-out Gremlin....I'll be testing it in the water tomorrow, hopefully it's gone.

But, while I was changing the plugs, I decided to go ahead and do a compression check on all the cylinders....

1,2,3,5,7 all @ 120 PSI
8 @ 140 PSI
4 @ 110 PSI
6 @ 90 PSI

All the plugs look good.

What does this mean....I'm figuring that it's just the fact that I've got 560 hours on a 350 Magnum and it's getting tired - but is this a sign of bad things to come?

Thanks,

EG

[Formula Jr]

Check #6 @g@in. If its till 90 psi, pour @little oil in to the cylinder @nd test @g@in. If it comes up then the rings @re b@d. If it does not come up, the v@lves on 6 @re worn. In the Chevy w@y of doing things 6 & 8 @re the two St@rbo@rd re@r cylinders. Your Low @nd High re@dings. If you tested with @ll the other plugs in, there m@y be more going on here. Like @ he@d G@sket f@ilure. @ 90 @nd @ l40 on the s@me engine isn't good news... frown

[MOP]

Most manufactureres allow a 25% margin on 4 stroke engines (10% on two strokes) yours is past that margin. You might want to try carbon buster, OMC, Merc, West Marine and I am sure lots more make it. There is a possibilty you have carbon stuck rings that stuff will free them. Follow the cans directions, and it is good to change theoil afterwards. Don't get it on you and hose it off anything it gets on. I have seen 30-40 psi increases. Our shop used it during every tune up and still does. My Michael got a free car back a few years was a clean little Ford, his intent was to drop a motor in it. I said why it only had 80,000 but smoked like blazes from the pipe and breather. Two treatment of the OMC stuff made him a believer for life, its still carting him and his with the same motor. Some of you guys know I go down to Costa Rica a couple of times a year, the gas there is on the poor side. I bring a few cans with me and do my freinds cars every years. They think its magic! I say give any low compression or smoker a try. Its about $6 bucks a can. If the above does not work break out the wrenches, no sense in letting it get worse.

[Blewbyu]

Eric-Were you on Lk Washington today???Saw a yellow Donzi Z boat go past-but it had 2 oval windows......don't you have just one per side?
Hope you got your problem solved.I'm on vacation 'till Sep 1, so if you get on the lake be sure to call or stop by. :D

[Formula Jr]

Henry s@ys Eric's Bo@t h@s one port hole per side. :)

[EricG]

I was out there gettin' beat up....but I didn't go past your place. The 2 port Holer was either a Z29 or a Z33...if it was yellow - that means it was probably either Andre from Kenmore or Buckley from Renton....both very, very cool boats!!

And yes, Henry can vouch for the port holes on my boat.....Owen, I just happened to have some screen material buried in the garage...so the boat is good as new ( or at least that part of it is :D ).

BTW - I checked the compression again....I was wrong, it was #4 that was low, not #6. And this time I got 120 in all but 8 (still 140) and 4 - which was 100...I'll try the oil trick next week. Thanks for all of the advice!!

-EG

[Blewbyu]

I'm inclined to always believe Henry!But, if I hadda brain in my head I probably would have noticed the pitcher below your name on the above!!!!!Duhhhhh....... :rolleyes:

[HyperDonzi]

with out checking compression is there a certain time when this should be done?
ie.oil every 100 hrs

[MOP]

I hope you are doing compression with the engine pretty well warmed up, coil grounded and throttle wide open. If not you will get whacky readings, look in any service manual that is the recommended procedure.