30 psi compression in 1cyl what to do?

[parrisw]

Re: 30 psi compression in 1cyl what to do?

Here is the damage. Not sure what happened, looks like maybe a piece of a ring?? Needle bearing? Anyway, there is a hole in the piston. And the cylinder below it, has a bit of play in the piston to cylinder clearance, so I'm thinking a set of pistons and rings, and it'll be good to go. On the damaged cylinder there is a slight amount of aluminum transfer from the piston onto the cylinder, which I'm sure will clean up fine. Where is a good place to buy pistons?

 

[wilde1j]

Re: 30 psi compression in 1cyl what to do?

You need to determine the cause of failure, or it will likely happen again.

 

[parrisw]

Re: 30 psi compression in 1cyl what to do?

You need to determine the cause of failure, or it will likely happen again.

Yes, I agree. Any thoughts? It didn't effect any of the other cylinders?? So what could it have been? I will be stripping it down for sure and inspect everything.

What do I have to do to remove the powerhead? Just remove the 4 mounting bolts and disconnect the electrical cables, and shift and throttle cable? Is that it, then pull it off?

Thanks for any help!!

Will

 

[wilde1j]

Re: 30 psi compression in 1cyl what to do?

Will, do yourself a favor and get an OEM shop manual before you start. Not sure what caused the failure from your photo, but it looks like a piece of metal went thru the piston.

A shop manual will help prevent expensive mistakes, like mixing up bearings and cages (they all need to go back exactly where they came from), etc.

I assume both pix are the same hole. Looks like lots of metal beat up the piston. Probably a bearing, but disassembly will tell more.

Parts are avaiable from Iboats, powerheadkits.com, among others.

 

[parrisw]

Re: 30 psi compression in 1cyl what to do?

Will, do yourself a favor and get an OEM shop manual before you start. Not sure what caused the failure from your photo, but it looks like a piece of metal went thru the piston.

A shop manual will help prevent expensive mistakes, like mixing up bearings and cages (they all need to go back exactly where they came from), etc.

I assume both pix are the same hole. Looks like lots of metal beat up the piston. Probably a bearing, but disassembly will tell more.

Parts are avaiable from Iboats, powerheadkits.com, among others.

Thanks, yes I did order a shop manual, I posted the link to the manual I got earlier in the thread. Then indentations in the top of the piston kinda look like a needle bearing. I'd like to get the powerhead off though now, cause I'm taking the boat over to a friends to store it, but I'm keeping the powerhead here to work on it.

As for parts, I looked here on Iboats, and it was very confusing to find the pistons, couldn't find any applications at all??? Just a bunch of piston shown? Anybody know how to look them up?

Thanks allot.

 

[wilde1j]

Re: 30 psi compression in 1cyl what to do?

Before you buy any parts, the marine machine shop doing the boring, etc. will have to mic the bores to see if all need boring and the oversize needed. If it were mine, I would do all holes, which means all new rings, pistons.

Look at BRP Evinrude website to see what the block assembly consists of. I would take off all the external stuff like starter, carbs, fuel pump, etc. before removing the block and disconnect all the electrics. The block is typically held to the mid by 4 to 6 bolts and/or studs. Use a harmonic balancer puller connected to the flywheel to lift the block, by looping chain or nylon rope under the puller. The block is fairly heavy (~ 150 to 250 lbs.).

 

[parrisw]

Re: 30 psi compression in 1cyl what to do?

Before you buy any parts, the marine machine shop doing the boring, etc. will have to mic the bores to see if all need boring and the oversize needed. If it were mine, I would do all holes, which means all new rings, pistons.

Look at BRP Evinrude website to see what the block assembly consists of. I would take off all the external stuff like starter, carbs, fuel pump, etc. before removing the block and disconnect all the electrics. The block is typically held to the mid by 4 to 6 bolts and/or studs. Use a harmonic balancer puller connected to the flywheel to lift the block, by looping chain or nylon rope under the puller. The block is fairly heavy (~ 150 to 250 lbs.).

Thanks. I'll find out spec on the bore, but it really doesn't look as if it has much wear, there is no lip on the cylinder and can still see cross hatch, I'm hoping to stay away from the machine shop if possible, hopefully just hone all the cylinders, new STD pistons and rings, bearings. I'll definitely take it all apart first before ordering parts. There is a lifting eye on top of the block, 150lbs isn't much, I could just lift it off with an extra hand, otherwise I'll bring the chery picker home from work.

 

[parrisw]

Re: 30 psi compression in 1cyl what to do?

Hmm, just got a line on a very good used engine, 1985 model 115 for a really good deal!! Maybe go that route. Save some work. Then use this motor as a project??

 

[wilde1j]

Re: 30 psi compression in 1cyl what to do?

Looking at the bores means nothing. You need to check for round and take multiple bore measurements with an inside mic. If I recall, 0.002 is the allowable wear limit from nominal. A good used motor may make sense, especially if the price is right.

 

[parrisw]

Re: 30 psi compression in 1cyl what to do?

Looking at the bores means nothing. You need to check for round and take multiple bore measurements with an inside mic. If I recall, 0.002 is the allowable wear limit from nominal. A good used motor may make sense, especially if the price is right.

I've rebuild enough motors without boring the cylinders, I do know what I'm looking at. Not everything has to be machined all the time, I realize if it was a customers motor then yes do it right, but the other 3 cylinders are building 120 psi compression on old pistons and rings, that's plenty of compression, it wont be any worse with new pistons and rings.

Anyway, I'm hopefully going to look at this other motor today, the guy says its a 1 owner mint condition, the guy traded up to a 4 stroke. I'll report back once I find out more.

 

[Bifflefan]

Re: 30 psi compression in 1cyl what to do?

Anyway, I'm hopefully going to look at this other motor today, the guy says its a 1 owner mint condition, the guy traded up to a 4 stroke. I'll report back once I find out more.

Hope that this one pays off for you.
As to the other one, that sounds good, work on it as you have time and then youll have 2 good ones.
Also I totally agree that as long as the bore is good then just a new piston would be fine, as the other holes are working good. Theres no need to over due it.
Just one thing, Im wondering about the needle bearing thing, Where did it come from if that was indeed what made the dents?
From the pic i think it may have been a small peice of the missing piece of piston that did it before it disapeared. Or a broken spark plug, that was already replaced. But maybe not.

 

[parrisw]

Re: 30 psi compression in 1cyl what to do?

Hope that this one pays off for you.
As to the other one, that sounds good, work on it as you have time and then youll have 2 good ones.
Also I totally agree that as long as the bore is good then just a new piston would be fine, as the other holes are working good. Theres no need to over due it.
Just one thing, Im wondering about the needle bearing thing, Where did it come from if that was indeed what made the dents?
From the pic i think it may have been a small peice of the missing piece of piston that did it before it disapeared. Or a broken spark plug, that was already replaced. But maybe not.

Thanks!! Good thought about the spark plug, could of easily been it!! Could be part of the piston too.

 

[parrisw]

Re: 30 psi compression in 1cyl what to do?

Just talked to the guy about the motor, he is back at the end of the week, should get it then. He says its a cherry one, in like new condition, its coming from a marine shop, and he said he had the mechanic totally go through it full tune up and everything, carbs, fuel system, water pump, so should be good to go, can't wait!!!! If my boat did 38mph with that old buggered engine running on 3 cyl's, cant wait to see what it does with this newer really good one. I'm hoping for at least 45mph.