No Compression in either Cylinder??

[Intermediate Mariner]

Morning Gents,

Whew, I must be doing something wrong but I'm trying to ck compression on a '62 40hp evinrude. I have the powerhead on the bench.

I cannot warm up but from what I've seen that should not make too much difference.

I installed head w/ old gasket as to not use a new one but it's tight. Also plugged every tube, nipple and hole that I could.

Starter is installed and fully operational. When I give it the juice I get NOTHING... in EITHER cylinder! Either one! I thought surely I'm doing something wrong because although I have scoring on one cylinder, the other is super smooth, but yet nothing on either one.

I can put my finger over the other spark plug hole and can fell the air flow pretty good but nothing. The gauge is brand new and I checked comp on car to be sure it works (and get 30). You would think you would get at least some reading!?!?

I am gathering that PH does not need to be mounting on lower leg since it's just exhaust.

Any ideas!

Thanks
Shawn T
Wichita KS

 

[cedarjunki]

Re: No Compression in either Cylinder??

either your not holding the tester in tight/ turning it over enough or its just plain no good. if only 30# in your car, it would not run!

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

Thanx for the tip Cedar. When I said 30 in the car I meant 30 with the gauge in and the engine running if that makes a difference. I just wanted to try to see if the darn gauge even worked and it appears to (harbor freight cheapie).

The gauge is the screw-in type and I got it in 5-6 threads so I figure it's deep enough.

I was mainly wondering if there are any other holes or passages that I should plug so the powerhead can build pressure? Also cranked it 10 revolutions or more and nothing.

I can feel the air from the other spk plug hole so shouldn't I get SOME reading? I mean aren't these supposed to be around 90psi?

 

[cedarjunki]

Re: No Compression in either Cylinder??

Thanx for the tip Cedar. When I said 30 in the car I meant 30 with the gauge in and the engine running if that makes a difference. I just wanted to try to see if the darn gauge even worked and it appears to (harbor freight cheapie).

The gauge is the screw-in type and I got it in 5-6 threads so I figure it's deep enough.

I was mainly wondering if there are any other holes or passages that I should plug so the powerhead can build pressure? Also cranked it 10 revolutions or more and nothing.

I can feel the air from the other spk plug hole so shouldn't I get SOME reading? I mean aren't these supposed to be around 90psi?

if you had it screwed in on the car and it was running............ that gauge is trash.... should have read 140ish depending on engine.

not much knowledge on outboards but my sleds usually need roughly 100# to run . around 110 sounds about right.

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

Cedar,
Thanks.
Hmmm... I'll bet you are right on that gauge. Yes it was indeed only 30psi on Dodge Dakota 5.2 V-8 while running. I will get another gauge and will post results here.
PS: The whole reason I am trying to confirm compression is that there are some grooves in one of the cylinders. Everyone has said to ck compression to determine the motor's true condition. If compression is bad I know why... if it's good can I leave it or should I get block bored anyway?? Even if compression is good the grooves will be there still (hopefully it will just smoke a little more).

 

[tashasdaddy]

Re: No Compression in either Cylinder??

screw in tester has to screw all the way in to the washer.

 

[cedarjunki]

Re: No Compression in either Cylinder??

i have ran some pretty scored up/scratched cylinders on my sleds...
a test will confirm if it needs to be honed or bored...

......but did you have it running previously? start ok? run ok? what made you do a teardown?

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

Thanks for asking Cedar. And I posted a few threads along the way but long story short: I got motor for $25, it was sitting in the mud but the guy said it was good. The lower unit was rusted but I replaced that already. I had to remove the PH because the shift shaft clevis nuts had fell off. I removed the head to have resurfaced and install new gasket (had water leaking before from warped head so didnt want to take any chances) as well as inspect cyl walls. I DID also find 8 or 9 metal shavings on top of the piston on scored cylinder side. I am ready to reinstall PH back onto lower leg now but I want to be sure since I do have several other blocks lying around but this one is so clean you could eat off of it (other than the grooves in the cyl wall) with no corrosion anywhere inside or out!

 

[cedarjunki]

Re: No Compression in either Cylinder??

in that case doing a compression test would be alot easier than pulling it apart twice.

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

OK, I got a new gauge.

One comes up 40 and the other at a big fat ZERO. Thats seems awful low even on a bad block.. is there anything I could be doing wrong?

 

[cedarjunki]

Re: No Compression in either Cylinder??

carb taken off or throttle wide open?
try adding just a little oil or something to lube and seal then try it. even wd-40 will work for this.


just thought about my first 40 horse johnson..... wow long time ago, good/bad memories..anyway, that had a decompressor to make for easier starting.....maybe froze open if yours has it? i think the johnson ran off the flywheel? not positive though.

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

Wow i never seen anything like it.. the one went from 40 to 60 pow. The other is still at a big zero though (the cylinder with the scores). the cylinder with the scores is the bottom one... there are some little grooves on one side of the wall.

The carb is removed.

So I guess i have a bad block then? Anything else I can try?

In looking to get it bored, I gather I have to go over-sized... with this course of action will I have to go with oversize rings AND oversize pistons?? The book has a .025 OS by the parts numbers... will my machine shop know what this means?

 

[1946Zephyr]

Re: No Compression in either Cylinder??

You could possibly even have some bad reed valves. If you found groves in the cylinders though, then it's a safe bet that your block is in rough shape. Post some pics of the cylinder so we can see how bad it is.

 

[cedarjunki]

Re: No Compression in either Cylinder??

In looking to get it bored, I gather I have to go over-sized... with this course of action will I have to go with oversize rings AND oversize pistons?? The book has a .025 OS by the parts numbers... will my machine shop know what this means?

if they dont find a better machine shop

If you found groves in the cylinders though, then it's a safe bet that your block is in rough shape. Post some pics of the cylinder so we can see how bad it is.

yes, pics,pics,pics

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

I can look into intake and see the reeds and they look good and smooth.

I'll say this though... that bad cylinder shoots out strong bursts of air that arent any weaker than the good one. It sthe wierdest thing. The grooves are not that deep. I'll post photos soon, I have to pull head back off and I want to try everything first.

Does it for sure not matter that block is on the bench and not mounted on lower leg? They say throttle open (carb is off). Thermostat cover is on (no gasket though). All misc. brass elbows on blocked plugged, should they be open? Does OTHER spark plug hole need to be plugged?

 

[cedarjunki]

Re: No Compression in either Cylinder??

are you absolutely positive the head gasket is good??
shouldnt need to plug anything.

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

Slapped an old head gasket in to do the test but it looked good.

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

Here's the pictures of the offending cylinder. After spraying more oil in both cylinders after photo I did a final check. The top was up to a strong 90 and the bottom a weak 30.

So, the best course of action would be to re-sleeve the bad cylinder, replace the rings and call it good?

 

[Intermediate Mariner]

Re: No Compression in either Cylinder??

I don't know if I should start another thread for this but I have a slight dillema as to which rings to order, I can find no cross-reference.

I am working on a 62 40hp evinrude. The actual original part number is 378430/0378430. The closest I can find is 380108/0380108... I cannot find a ref to a replacement part number.

I have been comparing BRP's parts catalogs from a '68 to my 62' and nearly every number is the same.

 

[cedarjunki]

Re: No Compression in either Cylinder??

Here's the pictures of the offending cylinder. After spraying more oil in both cylinders after photo I did a final check. The top was up to a strong 90 and the bottom a weak 30.

So, the best course of action would be to re-sleeve the bad cylinder, replace the rings and call it good?

that really doesnt look all that bad... no im not saying its good either.

but ive seen much worse than that run holding descent compression.
i might try just honing it first to see if it will clean up a little, but thats just me. since it is a boat motor maybe spending a little money on it and having a shop bore it or resleeve it may be better in the long run. my sleds are a bit different since if it does die i can just walk home, out in the water id rather know its good!


sorry i cant help with part numbers, but start a new thread and im sure someone will have them.