Cylinder Wall Scoring

farmallboy15 · Sep 7, 2023

How critical is a little bit of cylinder wall scoring?

I have a little 2 cylinder Mitsubishi diesel that I got non-running. After some tinkering, it ran fairly well but was terribly hard to start and had awful blow-by. Tested compression and cylinder 2 had acceptable pressure, cylinder 1 was down to 300PSI (~100psi lower than #2). Upon tear down both cylinders had busted oil control rings. #1 had a cracked piston to boot.

When the rings busted they left scores on the cylinder walls. #2 cleaned up pretty easy with a hone. #1 still shows some marks. Is it critical to get it bored and the score marks removed or for low hp, low rpm and low use, should I just run it?

fastfarmall · Sep 7, 2023

Are ere over size pistons available, its going to cost, the compression should increase with the new rings to get it started !!

farmallboy15 · Sep 7, 2023

Oversized pistons are available and I have to buy new pistons anyways Im thinking the cracked piston was the biggest issue with compression. But looking for some BTDT opinions.

Majorman · Sep 7, 2023

Not an expert on those engines by any means but I have seen a lot worse scoring on bores than that and been still OK. New rings would be the first thing I would try, along with the new piston.

tractorsam · Sep 7, 2023

Hard to tell just how bad it is from the pictures but I think it would probably be just fine, especially for lighter use. Id certainly try it. It may burn a little oil, it just depends on how far you want to go and what kind of end result you want.

Hobo,NC · Sep 7, 2023

It will hunt but never be a total seal it will affect it in some way.

DPittman · Sep 7, 2023

Since you are buying pistons anyway, Id spend the extra on some machine work and be done with it.
Just 2 cents worth

UncleTom · Sep 7, 2023

That looks so minor to me.

Dennis P · Sep 7, 2023

If you are going to buy new pistons anyway, bore it and install oversized pistons and remove all doubt.

Geo-TH,In · Sep 7, 2023

30 years I had many places in town to do machine work. Now they have all gone out of business.

If you can find a machine shop, why not buy oversize pistons?

tomturkey · Sep 7, 2023

Can you catch a finger nail on those score lines? I see they disappear near the top. A lot of advice here, some is costly, others not so much. If it fits in the budget, larger pistons and a rebore seems to be the best, but if not, standard pistons and new rings will PROBABLY/maybe get you where you would like to be. How far do you go, where do you stop, its always a crapshoot. I wish you well. gobble

Mike M · Sep 7, 2023

Anyone have any ideas on how the oil control rings got so busted up ? The bores look good ? but how do they measure ?

rustred · Sep 7, 2023

you need to measure the land clearance on the top ring. if its over.002 time for pistons. if that was my own unit i would not worry about those 2 scratches. the pistons will tell your story.

caterpillar guy · Sep 7, 2023

Kind of like an auction pay your money and take your chance. If in a daily runner with lots of use then bore it and new piston whether you sleeve it and keep the original bore or over bore it and bigger pistons is your choice. If just a putter tractor with little use and not heavy then just get a new piston and ring it. Unless you are going to keep it for many decades it will out last you with just rings and a new piston.

37 chief · Sep 7, 2023

If was mine, I would hone it a bit more, get a new piston, and be done with it. As someone else said the top is the most important, and looks good. Stan

the tractor vet · Sep 7, 2023

Well before ya get all carried away here and before ya end up costing your self more problems . First ya need to see how OUT OF ROUND the holes are and how much tapper and HOW MUCH WARE. Honing with a deglazing hone only follows the bore and will not correct and out of round or tapper , same goes for the ball hones . You set there with a deglazing hone you would be surprised just how much meat ya can remove and add to the already problem . When done ya can end up with piston slap and that leads to break skirts off the piston . Being just a two cylinder boring the block will make it ROUND again then the new oversize piston will fit like it should rings will seal like they should and compression will be back to where it should be and this will make starting easier . PLUS when done right it will live a long and happy life . Next thing i would do is have the injectors tested and the pump gone thru . Nothing will shorten the life then bad injectors and a pump over fueling.

farmallboy15 · Sep 7, 2023

Appreciate the advice Vet. Sounds like $200 and only a week turn around to bore it out. Rest of the hard parts are ~$800. Machine work is probably money well spent in the long run

T.R.K. · Sep 7, 2023

Get it bored for oversize pistons. You'll be glad you did. Take your crank to the machine shop and get it miked as well. NO use in putting it back together just to find the bearings are too loose. Also, have your machine shop check the valves and seats.

If you want to fix it (and have the money) fix it right. You are in too deep to stop now.

Also, If I am seeing the picture right, those ring grooves in that piston seems to be worn and there is too much side clearance for the rings.

Gene Davis (Ga) · Sep 7, 2023

Starting fluid will do that to the small Japanese diesel engines. Just ask me how I know. it has happened twice to my 650 Deere compact diesel made by Yanmar.

buickanddeere · Sep 7, 2023

I agree that while treating the symptoms is required. Still have to find the cause of the problems and eliminate it .
As new pistons have to be purchased. May as well bore the block .

This post was edited by buickanddeere on 09/08/2023 at 06:27 pm.

Cylinder Wall Scoring

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