Loss of power, won't plane

[Beakster]

Hi,

I have a J100TRLCSC and when I was out the other day everything was great, until it wasn't. I was pulling a tube and after swapping riders and restarting the engine I couldn't get up on plane. Boat seemed really down on power and was difficult to start. It wasn't a gradual thing, it was like perfect one moment and then next time I started I had lost power.
Pulled the plugs, here's a pic. Got new ones.

I did a compression check today and got:
110
120
90
110

So cyl 3 is a worry. I have an endoscope I'm charging up now so will take a look inside tomorrow. After a bit of searching on the forum I see that sticky rings could maybe cause this and running a bottle of sea foam through might clear it?

Do you think the low compression is causing my issue or could it be something else like a block in the carb?

While doing the compression test I noticed that after turning the engine the starter wasn't always popping back into place. It was staying engaged with the fly wheel. I'm wondering if it stayed engaged when I was on the water and that was causing the loss of power?

Any parts I need take about a week to come, I'm thinking I should order a carb rebuild kit and a head gasket. Then if the seafoam doesn't improve things I'd rebuild the carbs, and if that doesn't work I'd take the head off on the low comp cylinder and see if a new gasket will fix it.

Any advice much appreciated. Thanks

 

[racerone]

Sounds like the CLASSIC broken piston ring issue.---Pull that cylinder head.----Lucky you if it is a blown head gasket.----Every one of these engines will suffer from broken piston rings.

 

[Beakster]

Sounds like the CLASSIC broken piston ring issue.---Pull that cylinder head.----Lucky you if it is a blown head gasket.----Every one of these engines will suffer from broken piston rings.

Thanks for the reply. I got a borescope into the cylinder with the lower compression. Here's a video:

I'm a little reluctant to pull the head as I feel that once I do that the boat won't be going back in the water until next year. Based on the video does it look like piston ring issue? I'm still hoping its something fuel or ignition related. If there's no hope on getting some use out of the boat this year then I'll accept it and begin a full engine rebuild. I expect I'll need to buy an engine hoist and a few other tools and it will probably become a winter project.

 

[racerone]

Pull the cylinder head.----Looks to me like it needs rebuild now.---Sure looks like the classic broken ring issue.

 

[Beakster]

Pull the cylinder head.----Looks to me like it needs rebuild now.---Sure looks like the classic broken ring issue.

Ok will do. I'm reading people saying that you should warm the engine before removing bolts. Should I try to run it for a bit first? Or use a heat gun?

 

[racerone]

On a fresh water motor the bolts always come out for me.----Have done more than just 1 of those engines.-----I do not have enough fingers and toes to keep track of how many I have seen with this issue !!!

 

[Beakster]

On a fresh water motor the bolts always come out for me.----Have done more than just 1 of those engines.-----I do not have enough fingers and toes to keep track of how many I have seen with this issue !!!

Great to hear. I'm in the Laurentians so I believe this engine has always been fresh water. I'll start pulling it apart and report back with more questions soon. Thanks

 

[racerone]

Not much salty water north of Montreal.

 

[Beakster]

Finally got some time to open this engine up. Side cover for cylinder 3 looks to me like part of the piston ring is missing. Can someone confirm from this photo? This is my first time inside a boat engine.



The bores don't look great on any cylinder, and there appears to be some damage to the head of cylinder 1 although that was a cylinder with good compression so I'm wondering if it was damaged previously and then out back together in this state. Is the head reusable in this condition? Should I file the dents smooth with a Dremel or buy a new head?

 

[racerone]

See post #2 on this.----Correct as clearly stated this----BROKEN RING SYNDROME -----Is very common.-----Your motor has the disease.-----Needs to be torn down for rebuilding.----Many will not believe it , I see this damage all the time.-----Easy fix for me.

 

[Beakster]

See post #2 on this.----Correct as clearly stated this----BROKEN RING SYNDROME -----Is very common.-----Your motor has the disease.-----Needs to be torn down for rebuilding.----Many will not believe it , I see this damage all the time.-----Easy fix for me.

Im assuming that I need to pull the powerhead in order to do the rebuild? Do I need a hoist for that or can it be done by hand?

 

[racerone]

Yes you have to pull the powerhead off.----I used to be able to lift one of those powerheads off by myself.-----That is when I was the highschool wrastling champion.-----Powerhead does not weigh much much more than 120 lbs once you have the flywheel and starter off.-----And , yes you need 4 NEW pistons.-----It is a mistake to put new rings into worn ring grooves on those crossflow motors !!

 

[Beakster]

Yes you have to pull the powerhead off.----I used to be able to lift one of those powerheads off by myself.-----That is when I was the highschool wrastling champion.-----Powerhead does not weigh much much more than 120 lbs once you have the flywheel and starter off.-----And , yes you need 4 NEW pistons.-----It is a mistake to put new rings into worn ring grooves on those crossflow motors !!

Thanks. Can I reuse that cylinder head that appears to have some ding marks on it?

 

[tphoyt]

Personally I wouldn’t use a damaged head.

 

[racerone]

Remove any ring bits embedded in that head.-----Use small ball peen to knock down any bumps.-----Both heads are warped to some degree.----They all are.----So refinish it with a piece of glass and valve grinding compound.-----Then reuse it..----There will be no issue with it.

 

[Faztbullet]

Someone all ready replaced 1 piston as it .020. Typical cheap DIY repair, fixed the damaged cylinder and put the other 3 old pistons back in with rings.. Just a ticking time bomb as when other cylinder/s fail and looks as it as went off. Need to bore and replace all 4 pistons

 

[racerone]

Good eye.----I missed that 0.020 on that one piston.------I also stated that it needs 4 new pistons.----Well maybe 3 after inspection of all the bits.

 

[Beakster]

Thanks. Does this mean I should have all four cylinders bored to 030 over?

Any recommendations on a rebuild kit?

 

[racerone]

Inspect your bores , measure the bores , measure pistons at bottom of skirt. and post your numbers.-----Then make decisions.

 

[Faztbullet]

From the wear shading around the ports and the crappy job someone did honing. I would bore it .030 and slap a WSM kit in it. Install new deflectors, t-stat/poppets and impeller.