Low power?? Compression?? (1978 chrysler 35hp)

[bigchunkytaco]

ok so after working out all my water pumping, missing parts and gear issues i got this '78 chrysler 35hp on the water pumping water ok (although the water stream is quite hot but didnt seem to overheat.)
i am unsure of what kind of power to expect from a 35 however i am certain it seemed to be quite low. was advised it should pull a ski biscuit but there is no way as is...

at first i thought it could be a fuel problem because it would die when i increased the throttle, i found a crack in the fuel indicator/ hose attachment plate on the tank so im patching that up tonight however cant imagine the fuel would prevent it from revving out before running dry.

however something is telling me its a low compression in one of the cylinders. the top was running 125psi which should be fine? but the bottom i cant fit my compression tester into, i got a reading of 25psi but am unsure if it was even screwed in all the way. it does feel lower wen i hold my finger over it, i cant see what else it would be. the spark plug also looked a little black but im unsure if its oil or burnt, does have good spark.

i havnt taken the head off as yet, as i was going to test it on the water by only connecting one plug at a time.. unless running the boat with a low/solo cylinder would not be advisable mechanically..

presuming the 25psi reading is correct would it just be the head gasket, or rings? or something more serious...?

any ideas from the wise iboat community would be greatly appreciated!

 

[TwoFish]

Re: Low power?? Compression?? (1978 chrysler 35hp)

It would be good to get a comp test on the bottom cylinder before you go to the trouble of pulling the head off.

I bought this tester from Repco. It has a very short fitting. I would imaging if you could get a spark plug into the motor you would get this design comp tester in also.

Noticed that you are from Australia. If you are from Adelaide you would be welcome to borrow mine.

Cheers

Dean

 

[jerryjerry05]

Re: Low power?? Compression?? (1978 chrysler 35hp)

Like Dean said,a compression reading is a MUST to start any diagnosis.You can remove the head and look but if it starts easily then you might have a fuel problem and not a compression problem.The fuel pump could need rebuilding or U could have an air /fuel leak.
How's the spark.
Start with the basics.Compression,spark then fuel.J

 

[bigchunkytaco]

Re: Low power?? Compression?? (1978 chrysler 35hp)

hah thanks mate i am actually in sydney but appreciate the offer! found a comp tester with a smaller fitting and it was low so pulled the head off and its not real pretty, thebarrels themselves seem to be ok with execption around the exhaust ports..
the head of the cylinder and actual head both have scoring as per the pictures.. you can also see the ring is buggered from that close up shot..

now, im assuming i need at minimum rings and gasket kit, however can you get away with the piston and the head being in the condition they are or will i need new psiton and head also. these parts arnt easy to source in my area and arnt particularly cheap so im wondering if its worth salvaging...
and if so is there any easy way to access the pistons to at least change the rings..
thanks for the input!

 

[jerryjerry05]

Re: Low power?? Compression?? (1978 chrysler 35hp)

New piston and head.Get a different motor.It would be way cheaper to replace than repair.Keep the old for parts.J