1978 35 hp evinrude compression question

[scuba_redneck]

Hey guys! I have found a guy locally who has a 1978 35 hp evinrude that he is trying to sell. It has 60 psi compression on the top cylinder and 65 psi on the bottom. The spark plugs had black tips and chocolate colored porcelain. If my memory serves me correctly they are j4c's. The guy selling it told me that he has trouble starting it but once it fires up it runs he had it on a 12 foot 36" wide flatbottom aluminum boat but separated then due to safety issues of too much motor. How do these compression numbers stack up to normal specs?

 

[scuba_redneck]

Re: 1978 35 hp evinrude compression question

Oh yeah, I forgot to include that the model number is 35852r electric start

 

[boobie]

Re: 1978 35 hp evinrude compression question

They sound low but try a different compression gauge. Are both plugs out when checking it ??

 

[scuba_redneck]

Re: 1978 35 hp evinrude compression question

Yes both plugs were out when I checked it. Compared to my '73 18 hp that I worked on back in the spring it took forever for this head to pressurize my gauge. The flywheel rotates easily with the plugs in which leads me to believe that those numbers are correct. I will retry them with another tester when I get back around the engine

 

[AlTn]

Re: 1978 35 hp evinrude compression question

if those numbers are correct using the electric starter for the test, then they are realllly low compared to using a manual starter...is it priced cheaply enough to do the required work to get the compression up?

 

[JB]

Re: 1978 35 hp evinrude compression question

That could be carbon sticking the rings or it could be head gasket leakage. Either would be easy to correct.

My judgement is based on the pressures being close. I would expect major damage to make one cylinder much lower than the other.

 

[scuba_redneck]

Re: 1978 35 hp evinrude compression question

I tested it with a dry and wet compression test. I used WD-40 as the oil to do the wet test to check the rings. I turned the motor over for 5-10 seconds per cylinder using the electric starter. It averaged about 7 seconds to fully pressurize the tester. There was no difference in wet and dry test pressure results.

 

[scuba_redneck]

Re: 1978 35 hp evinrude compression question

Also, I have never had a chance to break open a head to inspect rings or pistons. How much work/ money/ parts are we talking to get an inspection done. I am already figuring on the gaskets and seals, I was wondering if the rings are carbon caked what to do

 

[JB]

Re: 1978 35 hp evinrude compression question

Also, I have never had a chance to break open a head to inspect rings or pistons. How much work/ money/ parts are we talking to get an inspection done. I am already figuring on the gaskets and seals, I was wondering if the rings are carbon caked what to do

If you got the same result wet or dry it is almost certain to be head gasket leakage between cylinders.

 

[Solittle]

Re: 1978 35 hp evinrude compression question

Also, I have never had a chance to break open a head to inspect rings or pistons. How much work/ money/ parts are we talking to get an inspection done. I am already figuring on the gaskets and seals, I was wondering if the rings are carbon caked what to do

Pulling a head is easy and head gaskets are relatively cheap. You will not be able to tell if the rings are coked up with the head off as the pistons will be in the cylinders. When you get the head off make sure that it is not warped. If it is take it to a machine shop. One other thing use a torque wrench to torque the head bolts and be sure to torque them in the proper sequence.

When you get it running do a decarb to clear the carbon/crud from th episton rings. Then retest the compression. I'll bet it jumps to around 100+ psi.

 

[Tvtrader]

Re: 1978 35 hp evinrude compression question

I am about to start work on a very similar engine.
It has the same compression as yours.
The previous owner said it had overheated and he shut it down.
A manual has been ordered and I will soon do an inspection.
Will keep an eye out to see how you make out.