115 6c TOP piston cylinder issue

[ianmoore]

Hey everyone. Posted an initial query, but now diving in deeper and wanted to post a more comprehensive thread.

mid 80's 6c TOP 115. s# 6525632

Started out with 0 compression in cylinder 3. Powerhead off.
Goal is to hopefully get engine going, but worst case, to learn a bit about it. I think the block is good. Definitely have some piston damage. Seem to be missing 2 rings on C3, and one on C6. From what I can see, there are nicks and scrapes at the squish band, but the main bore seems to be ok. This is just with a borescope though, and i had never used one before, so take that with a major grain of salt

I have a million questions, but want to be strategic about people's time.

I'm waiting on a flywheel puller to arrive, and trying to make sure I have everything out I can get out. I have all of the main crankcase bolts out. The manual is super vague about what is where.

Im a little scared of these end cap bolts, but I'll clean them up, spray some penetrating oil, torch them, and go slow. I'm assuming they are sturdy because of where they live.

My first big, dumb question. Once I get the crankcase cover off..What do i need to watch out for? More specifically, I know that everything in the assembly has to be in the exact order, and I need to take out the 2 bad pistons, and probably inspect them all. I am doing a ton of reading and going really slow, but I have 0 experience doing this and have always shied away from it.

But, i have a broken motor, and hoping to have a working motor.

So, necessity breeds ambition

 

[racerone]

Remove crankcase cover.-----Scratch one line on #1 rod cap up to 5 on #5 rod cap.----No need to mark #6 cap.----Need 1/4" 12 point socket to remove rod bolts.

 

[Chris1956]

End cap bolts usually come out easily. Not sure why yours are stuck.

Removing the outer flywheel (8 5/16" bolts), is usually all that is necessary, if the stator is good it can stay on.

Connecting rod screws need to replaced with new, after removal. Sometimes you need to grind down wrench to remove them. Use separate cups (numbered 1-6) for rod bearings, to keep them separate. Stick 'em back with grease when reassembling.

Check water tube in exhaust extension, while you have it apart. Look for crushing of water tube or water tube grommet damage. Replace as necessary.

Stock reeds are almost always good. Unless they are broken, reuse them.

You must rebuild the carbs, link and synch the motor and rebuild the waterpump, or issue is likely to happen again.

 

[ianmoore]

End cap bolts usually come out easily. Not sure why yours are stuck.

Removing the outer flywheel (8 5/16" bolts), is usually all that is necessary, if the stator is good it can stay on.

Connecting rod screws need to replaced with new, after removal. Sometimes you need to grind down wrench to remove them. Use separate cups (numbered 1-6) for rod bearings, to keep them separate. Stick 'em back with grease when reassembling.

Check water tube in exhaust extension, while you have it apart. Look for crushing of water tube or water tube grommet damage. Replace as necessary.

Stock reeds are almost always good. Unless they are broken, reuse them.

You must rebuild the carbs, link and synch the motor and rebuild the waterpump, or issue is likely to happen again.

I was just being cautious with end caps. I have never take them off before.
rebuilt carbs, fuel pump, and did a link and sync when I got motor 6 years ago. Up until the end of last year motor has performed admirably.

I looked at the tube and it all seems fine. Motor has always had a good stream. There were some pretty solid salt deposits, especially in the head plate. I don’t know enough about the architecture of the water/ coolant passages to know… I’ve always been thorough with flushings, so was a little bummed about all the deposits, but then again, I never looked inside the motor when I bought it
I had just synced motor when I found bad cylinder(it ran ok ok muffs). I rebuilt carbs when I got motor, and was planning on redoing at end of season this year- now plan is to rebuild now, assuming I can fix issues.
I figured removing the stator might be worth it to get cdi packs out of the way. Maybe not?

Thanks for tips. I am trying to go slow with it all to not make any catastrophic mistakes, and flying semi blind. Grateful for the info

Hopefully will have it open this week.

If cylinders are good and I have to replace a couple of pistons and rings, is

End cap bolts usually come out easily. Not sure why yours are stuck.

Removing the outer flywheel (8 5/16" bolts), is usually all that is necessary, if the stator is good it can stay on.

Connecting rod screws need to replaced with new, after removal. Sometimes you need to grind down wrench to remove them. Use separate cups (numbered 1-6) for rod bearings, to keep them separate. Stick 'em back with grease when reassembling.

Check water tube in exhaust extension, while you have it apart. Look for crushing of water tube or water tube grommet damage. Replace as necessary.

Stock reeds are almost always good. Unless they are broken, reuse them.

You must rebuild the carbs, link and synch the motor and rebuild the waterpump, or issue is likely to happen again.

just being cautious on end bolts. Never removed them before.

Water tube seems good, and motor has always had good tell tale. There were some decent salt deposits under head plate. Thinking maybe that was it? Ive replaced impeller every 1-2 years and it seemed to be getting good water pressure.

Will remove flywheel today. Was thinking of removing stator to get CDI stuff off the motor. Any reason not to?

Assuming im able to fix the issues with the bad cylinders, would you leave it at that, assuming the others look good?

Planning on rebuild of carbs and link and sync. I had just finished the latter when i found the bad cylinder, and the carbs were on list already to redo at end of season. I rebuilt them about 6 years ago.

Noted on rod screws and bearing. Thanks.

I thought the flywheel came off with the puller? That is what i ordered. Its in the merc manual

 

[Chris1956]

You can pull the flywheel, however, unless you need to remove the end cap, there is no advantage. Make sure you mark the stator wires. There are some pairs which must go to the same switchbox, for Ign to function properly.

Plan on installing all pistons into the bores after repairs, and then attaching the crankshaft to each connecting rod individually. Merc shows using 6 OEM ring compressors, but only shops have same, in my experience. If you have a strong helper who can hold the crankshaft steady, maybe you can install the pistons one-by-one when they are attached to the crankshaft.

 

[ianmoore]

I was under assumption that flywheel needed to come off to get top endcap off. I can't see a way to get to it with it on.
I'm gathering info from reading and watching videos. I know these earlier engines had the rod caps with the nuts below. Would this make attaching pistons to crankshaft difficult once they are in bores?

 

[Chris1956]

I am not sure I follow your comments. Here is my interpretation.

Endcaps will slip out once crankcase is split, and endcap bolts are out. If you need to replace endcap bearing, you will need to pull trigger, stator and flywheel. Upper and lower endcap bearings may be different types.

Older motors (pre 80's) had connecting rod nuts and bolts. These were reuseable. Newer motors have cap screws which are single use.

After all pistons are in their bores, you can lay the crankshaft into the block half and seat the end caps. Now you can grease the connecting rod bearing journals and stick on the roller bearings and cages, one at a time, pull them up to mate with the crankshaft and tighten them to spec.

 

[ianmoore]

I am not sure I follow your comments. Here is my interpretation.

Endcaps will slip out once crankcase is split, and endcap bolts are out. If you need to replace endcap bearing, you will need to pull trigger, stator and flywheel. Upper and lower endcap bearings may be different types.

Older motors (pre 80's) had connecting rod nuts and bolts. These were reuseable. Newer motors have cap screws which are single use.

After all pistons are in their bores, you can lay the crankshaft into the block half and seat the end caps. Now you can grease the connecting rod bearing journals and stick on the roller bearings and cages, one at a time, pull them up to mate with the crankshaft and tighten them to spec.

Please forgive my ignorance-- This is the first time to split a motor.
The top end cap in underneath flywheel(and i assumed stator). I can't get the endcaps off without removing this(at least don't think i cant)

My comment about connector rod and caps is concerning being able to reattach connecting rod to piston with piston in bore. On the marine engine parts list for my page, it shows the top screws that thread in, but on the merc manual it has screws that thread into nuts below. It it is the latter, would i be able to get the nuts on if the the piston is in bore?

 

[Chris1956]

Unless you need to replace the top main bearing, you do not need to remove the top end cap. So the stator can stay.

The crankshaft connecting rods can be connected with the crankshaft in the block. It is a bit easier with the cap screws, but fingers fit to hold the nuts, as if needed.

With the age of your motor, I expect you to have the cap screws. You might get a torque wrench, if you do not have one. The torque of the connecting rod screws is important.

 

[racerone]

These newer inlines use " cracked rods " and no need for fancy ring compressors.---Remove and install pistons one at a time.-----Flywheel and hub are easy to remove.----Careful / take time to get rod caps installed correctly.----They only go one way.

 

[ianmoore]

progress. I was getting a little confused, as you were saying i didn't need to pull flywheel, but i could not get a wrench around the end cap screws without pulling it. Got it off, and got crankcase open. I'm gonna do a little reading, clean up the shop, and get organized before i start digging in.

Thanks for the help so far! Cool to dig into it. Keeping my expectations reasonable, but moving along.
Chick a boom

 

[ianmoore]

OK. Got crankase out. I'm hopeful. Cylinder 3 actually looks pretty good. Cylinder 6 has about a 1" scratch that barely catches my nail on the right side. I tried to get pictures of the cylinders, but couldn't get the lighting right to capture them. Here are the 2 funky pistons. 3 is totally trashed. I don't know if 6 would be salvagable or not. Everything else, at least to my eye, looks totally normal. I don't see any damage where the pistons sit or anything

 

[Chris1956]

The missing ring on the "better" piston (piston 6??) concerns me. Did you find any pieces of it? You might measure the thickness of the ring groove, as it looks like it opened up. A new ring might just fall out as well..

I would be surprised if cylinder 3 and 6 do not need boring.

 

[racerone]

Measure the bores or consult a machine shop.-----Or use a ring from a good piston and check end gap in 3 and 6.

 

[ianmoore]

The missing ring on the "better" piston (piston 6??) concerns me. Did you find any pieces of it? You might measure the thickness of the ring groove, as it looks like it opened up. A new ring might just fall out as well..

I would be surprised if cylinder 3 and 6 do not need boring.

I think both 3 and 6 are bad. I spent 2 hours calling machine shops today and finally found one that can look at it..

 

[ianmoore]

Measure the bores or consult a machine shop.-----Or use a ring from a good piston and check end gap in 3 and 6.

I made a valiant effort to measure the bores but I just don’t have the right equipment.
I’m taking it to a shop to measure and recommend a course of action. The only cylinder damage I can see is a small scrape in 6, but I can’t tell what has happened beyond that. I think 1,3, and 6 are all .015, and the rest aren’t marked, which may mean “standard”. My measurements are in line with this, as 1,3, and 6 are @2.882 and the rest are @ 2.865

One question- I use marine engine as a parts ref since I can enter serial #. I bought the engine used, so not sure what was done before. All of my pistons have 3 rings and the pistons listed only have 2. It’s possible this isn’t the original powerhead, and I want to make sure to order the right pistons when I do. Do the new ones just have 2 rings, and/or is there a way to find out powerhead model, if different from stamp on bracket?

 

[ianmoore]

I got to machine shop and the guy couldn’t bore a blind cylinder. He felt bad(I drove 2 hours to get there) and is gonna reach out to another machine at he thinks can do it. It’s wild that this is so hard to find. Anyway.. Will post when I find anything out

 

[racerone]

Hard to find because there is very little call for this kind of work.

 

[Chris1956]

When rebuilding my '77 Merc 1500 IL6, replacement pistons had 2 keystone shaped rings. These replaced the original 3 square shaped ring pistons.

 

[jimmbo]

I remember 40 yrs ago, only a couple of Bike Shops, in a city of a Pop, of close to a Million, would machine Merc Inline Blocks