Considering Limited Rebuild of 1991 75hp 2-stroke - cylinders OK?

[propgun]

My outboard has developed some rod knock that sounds like a piston pin. It is only one cylinder from looking at the audio waveform. I have other posts on this.

Anyway, I'm waiting on the flywheel puller/lift ring tool since I can't figure out how to get the crankcase cover off with the block on the exhaust housing (middle section). I took some videos of the inside walls of the cylinders using a cheap HF inspection camera. There seems to be some scoring but I don't have enough experience to determine how bad it is. The compression readings are 110, 105, 110 (also using a cheap HF compression tester which might be reading low). I don't know if the attached videos are good enough for anyone to comment on as to whether or not the cylinders need to be resurfaced but I was hoping they might be. I took the videos with the right angle mirror attachment inserted into the spark plug holes looking up and made one full rotation clockwise even though the video looks like the rotation is counter-clockwise.

Any opinions or advice would be greatly appreciated.

I uploaded the videos to youtube - it says they or at least one of them will be at this address: 20130908103234 bottom - YouTube

I need to learn how to do a better job with posting pictures and videos :facepalm:

 

[propgun]

Re: Considering Limited Rebuild of 1991 75hp 2-stroke - cylinders OK?



I've attached a number of pictures of the top cylinder which I think is the worst. Also the other two videos are at:

20130908102946 top - YouTube and 20130908103115 middle - YouTube

 

[Faztbullet]

Re: Considering Limited Rebuild of 1991 75hp 2-stroke - cylinders OK?

You really cant go by looks, motor needs to be removed and split and cylinders miked.

 

[propgun]

Re: Considering Limited Rebuild of 1991 75hp 2-stroke - cylinders OK?

You really cant go by looks, motor needs to be removed and split and cylinders miked.

Thanks for the reply,

Do you have the measure the diameter (at multiple angles) in the middle of the cylinder as well as the back (which is easy?). My dad was a machinist and I think I have seen a mic that would measure inside the cylinder too.

I agree of course, I guess I have four options:

1) put new piston pin bearing(s) in assuming the rods are straight, the rod holes look round, and the pins don't look too warn and live with that if it takes care of the knock (the engine has all the power/performance I need from it now even with the tick of death)
2) put on a rebuilt power head ($2500 +)
3) try to do a more complete rebuild myself (would have to take it to a shop of course)
4) have a tech rebuild it (the problem with this one of course is no one (two) can give me any kind of not to exceed number until they open it up and I understand that but I am on a very limited budget.

5) (not a very good option) run it till it dies, get towed, and go with option 2.

The knock goes away when the engine is warm. For instance when I ran it back from the lift to the ramp yesterday I went maybe a mile at 2500rpm (trying to take it a little easy) there was no knock at idle for maybe 15 seconds so I'm thinking the parts expanded enough when they got hot. Of course, I guess there was knock, I just couldn't hear it.

I wish I could get the crank case cover off without lifting the power head off the middle section. Besides getting the wiring and hoses off and the flywheel off (which was not easy) I haven't made much progress. Have to wait for the lifting ring to come and then drive to the lake again (6 hours) and see if I can get the power head in the car. Was hoping to take home the crankshaft with three pistons hanging off it and then decide how much of that I needed to replace.:blue:

 

[wired247]

Re: Considering Limited Rebuild of 1991 75hp 2-stroke - cylinders OK?

Its a half hour job to pull the power head. Resign yourself to do the work and get started.

 

[1nebel0]

Re: Considering Limited Rebuild of 1991 75hp 2-stroke - cylinders OK?

Hey Wired....I love your post..kind of like pull up your boot straps and get busy!!!!!!

 

[propgun]

Re: Considering Limited Rebuild of 1991 75hp 2-stroke - cylinders OK?

The lift ring/flywheel puller tool is supposed to arrive tomorrow. Hopefully I'll be able to head back up to the lake and bring the powerhead back this weekend. I hope that is not too much delay for you guys.