1988 85hp Scored Cylinder

Hi Guys, I'm new to posting on the Forum but have been reading lots of posts/threads and got some really good information. Can someone advise me on a scored cylinder.

I had starting problems - seemed that one cylinder wasn't firing. Investigated - testing electrical components and then compression. Maybe should have done this the other way round, anyway #2 cylinder compression was way down on #1 & #3. I removed the head and there was no problem with the gasket but I've found some scoring in #2 cylinder. To me they don't seem to be too deep and there are only two areas affected but I don't have the experience to be sure.

Questions:
Are they light enough to hone out?
How deep a score can be treated before having to re-bore?
Will I need new rings once the cylinder is honed? (I know I'll need them if re-bored)

I'm not a mechanic but am handy enough to carry out most jobs on the engine, it's just I don't have any experience in this area and don't want to dive in making a fundemental mistake on the way. From other posts I learned that I can access the piston through the manifold and have now removed the carbs and reed valve assembly. I can now see the piston and can access the securing bolts. Before I disconnect is there anything I should be aware of? Any tricks or techniques? I don't want to disconnect and find difficulty due to lack of knowledge. I've got the Force service manual and don't see a problem from looking at the diagrams, other than perhaps relocating the bearing cages when it comes to re-assembly. Any tips or is it straight forward?

I've attached a couple of pics of the cylinder and add more if any more detail is required. Looking at the last picture (pic d) the score marks are at 12 o'clock and between 3 & 4 o'clock.

Any advice/comment would be most welcome. Thanks.

Re: 1988 85hp Scored Cylinder

Ok im looking at your picks and from what I can see you are looking at a rebor. Maybe picks aren't doing justice here but it looks bad. Check iboats for parts and another would be boats.net. if you do a rebor then yes you will need new pistons and rings. Im sure there will be other to post here with some great input to help you.

Re: 1988 85hp Scored Cylinder

What the actual compressions are would have been handy.....if you can catch your thumb nail in the score then its most likley a re bore job...though I have known people hone it and then fit oversize rings to standard pistons having adjusted the end gaps Its all down to how much you want to spend on the outboard/how long you are keeping it /ect ect ...
Mark the big ends for orientation when removing ..must be fitted as removed as they are line bored.. Count the rollers as you remove them so you dont leave any inside . You hold it together with grease when re fitting the big ends

Re: 1988 85hp Scored Cylinder

Thanks for the replies so far.

The compressions were 125, 70, 125

Re: 1988 85hp Scored Cylinder

The scoring is actually aluminum from the sides of the piston that has melted.
Profile:You might be close to someone who can help.Sent U a PM.

Re: 1988 85hp Scored Cylinder

yes if it aluminium then its probably new pistons but if you can use the old with oversize rings then put the new oversize ring in the top of the bore and file the rings so the end gap is 10 thou..

No doubt this problem is caused by over heating so if your motor does not have a pisser then fit one and observe its strength ..if it weakens go stright to the impeller.

Re: 1988 85hp Scored Cylinder

Do not put oversize rings on old pistons!

If it is not to far out of tollerence and will clean with another .001 or.002 go back with a new wiseco. Disassemble the motor and take it to a machine shop and have them hone it with a ridged hone.

Honing it assembled just puts grit in places you cannot clean and will eventually destroy the motor. You have come this far..........Do it right!

Re: 1988 85hp Scored Cylinder

Come on Sprky, you don't want to see those oversized rings roll off the piston and seize up the motor? You?re taking all the fun out of this!

Re: 1988 85hp Scored Cylinder

Your compression is down because the piston has rubbed-off some aluminum onto the cylinder wall. Because of this, some of the aluminum of the piston is rubbed into the ring grooves and sticks the rings below the piston level. Thus, the rings are no longer sealing against the cylinder wall.

It is possible to remove the piston and sometimes you can free the rings. Most times they are practically welded in though and will break if you try working the free ends. Depending upon the severity of the damage, you MAY be able to free them. Sometimes, using heavy leather gloves and heating the pistonwith a propane torch will help to free the rings. (it is preferable to heat them in the oven to 350-400 degrees but if you are with a woman, after doing that you won't be!) If you can free them simply clean the grooves and re-use the piston, provided that the piston is not too badly damaged.

Before installing the piston. Use a sharp tool to scrape the aluminum off the cylinder wall and then lightly hone it.

Do NOT use oversized rings. First off, I don't think they make them in the size you would need. Pistons and rings are made in .010, .020, .030, and .040 oversized. Wear tolerance is only .005 so if you used an oversized ring it would be out of round in the bore and would not seal properly.

NOW: If you can not free the rings but can hone out the scoring, then try finding a used standard piston and ring set (3.3125) and use it. No sense putting a brand new piston into that engine.

If you can not easily hone out the cylinder, then you must disassemble the engine and have it bored to whatever oversize will clean it up. In that case buy a new piston and ring set.

No matter what you do, remove and clean all three carbs then reset them correctly or the new piston will be damaged again.

Re: 1988 85hp Scored Cylinder

I understand the money thing...........problem is when you try and go cheap it usually bites you in the *****. I own a shop that specializes in outboard rebuilds. We have our own inhouse tooling and source nothing out. I probably have seen every "cheap" fix out there, 75% of the time it results in more damage. Yes, you can just address the one hole, yes you can put a used piston back in there, but for a few dollars more you can "straighten" the cylinder with a ridged hone, throw a forged piston in there (wiseco), go back together and have an decent motor.

Frank is right about the carbs. You should also install an new impeller and thermostat. The damaged cly. is just a symptom. You have to cure the origional disease to keep the problem from happening again.

I have quite a few customers that have me do the machine work and they do the rebuild themselves. If you take your time, pay attention, and ask the right people when you have a question you will do fine.

I hate to see something that could have been fixed with $200 to $400 turn into something that requires $2800.

Good luck

Re: 1988 85hp Scored Cylinder

Thought we were supposed to give out good advice here???

Re: 1988 85hp Scored Cylinder

Thanks guys some good advice and I really appreciate it.

A new impellor has been fitted, fuel pump diaphragm replaced and I'm waiting on the carb kits. If I'm going as far as replacing a piston, honing a cylinder I want to do it right (as sprky says) and I might as well do everything else at the same time.

I'll start with Franks advice and remove the piston and see what I can do with the rings, have the cylinder honed and then see how to go forward from there.
It'll take a bit of time to get to that stage as I work away from home and that interferes with the important things in life! I'll keep you posted on any progress I make.

Many thanks for all your time and effort in helping out so far. Anything else you guys can think of please add it to the thread.

Re: 1988 85hp Scored Cylinder

Howlin...........

I will make you a deal. You pay for the freight and I will do the machine work for free and tell you where you can buy parts for 20% over cost.

Do it right and be happy.

Chris

Re: 1988 85hp Scored Cylinder

Chris,

Thanks my friend that's a great offer and really appreciated - there's just one little problem - I'm located in Scotland!! Freight is going to be a tad expensive. Just getting spares shipped across makes my eyes water and those are the lightweight ones! .

Pete

Sprky said:

Howlin...........

I will make you a deal. You pay for the freight and I will do the machine work for free and tell you where you can buy parts for 20% over cost.

Do it right and be happy.

Chris

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Re: 1988 85hp Scored Cylinder

It's all in the details.....................My bad!

Is there anything else I can do?

Chris

Re: 1988 85hp Scored Cylinder

I have a high ring 3.312 in nice shape, no top ring though. It is yours if you need it, otherwise it goes to the recycler.

Re: 1988 85hp Scored Cylinder

This man is from scotland and very very mean ........common practice to use oversize rings in cars ..put ring in very top of bore (unworn) and gap to 10 thou before fitting ...

Re: 1988 85hp Scored Cylinder

fucawi said:

This man is from scotland and very very mean ........common practice to use oversize rings in cars ..put ring in very top of bore (unworn) and gap to 10 thou before fitting ...

Click to expand...

Ha, ha. Not just Scotland but Aberdeen - the very epicentre of thriftyness!! Renowned, no strike that......... revered..... even by the Scots

Chris,
Don't recycle anything until I've investigated further. It'll take a while to get to the full disassembly stage though, time waits for no man and I'm in short supply of it. Or maybe I should say - too many things to fit in to the time available.

Re: 1988 85hp Scored Cylinder

It's been a while - longer than expected but I finally got round to the repairs. Progress with dismantling the block was quite slow as work got in the way again. The piston when removed did indeed have the rings stuck and the piston itself wasn't in too good shape. I sourced another piston and rings but had to wait quite a while before they arrived.
During the wait I honed out the cylinder with a 3 stone hone and plenty of oil. This removed the aluminium deposited there from the overheated piston. Once that was done it was evident that the score marks were slight - I couldn't feel them with my finger nail and they honed out too. I checked the bore diameter and it was well within tolerance which was expected as the honing was light.
Eventually all the spares arrived - carb kits, piston/rings, fuel pump kit, gaskets etc. and I got time this last week to put it all together. Everything went (I think) relatively well, although I did experience one or two problems along the way. One being a cylinder head bolt stripped the threads in the block. How this happened I don't know. The bolts all came out without problem but when it came back to torquing down the head one bolt wouldn't tighten. ****! This had to be cleaned up, tapped out to a larger size and a repacement bolt fitted.
Replacing the piston and rings wasn't too bad. Removing the wrist pin was! Use of re-assembly grease greatly eased the fitting of the pin bearings on both rod ends.
Compression 130, 120, 131
Carbs were dismantled, cleaned and fitted out with overhaul kits.
Fuel pump (actaully done before all this work) overhauled with new diaphragm fitted, filters cleaned. Added filter after pump
Water pump opened up and new impellor fitted - now pumps lots of water.
Thermostat removed and checked for operation - ok.
Unable to remove plug on cylinder head to fit tell-tale. Don't want to strip another thread.
New starter solenoid fitted - all good.

I've now got it all back together BUT I've got a problem or two. I've linked & synched the carbs as per Franks sticky. One question about the throttle plates in the carb - the manual says make sure the letter stamps face out. Does this mean out from the middle of the carb or out from the engine i.e. the letters would face in to the middle of the carb?
Problem- I start her up and she fires, starts to run and then backfires a lot (exhaust side), so much so that the engine stalls.
The idle revs are very high. Tried altering the idle screw but still way high.
Removed carbs (needles at 1 1/4), cleaned and re linked/synched.
Found no spark on #1. Lots of digging around and discovered a broken wire which cured this
Checked timing - slightly out and adjusted to 28deg.
Used different fuel- no difference.

Need some help guys to cure this backfiring and the higher than should be idle revs.
Thanks for taking the time to read this long post.

Re: 1988 85hp Scored Cylinder

OK, got it! It pays to follow the link & sync procedure correctly, do what it says not what you (I) think it says! Doh!
Now to get the boat in the water and complete the idle speed checks/adjustments but that won't be for a couple of weeks as it's time to go away to work again.