Top-end rebuild advice needed

[flyingace]

I'm considering doing a rings only rebuild. I have a spare engine, and by mixing/matching pistons and bores, I can get the clearance between the bore and piston skirt (thrust side) below .06 mm on all cylinders.

Is this a bad idea? Should I just bite the bullet and rebore/rering with new pistons? The price difference will be $140 dollars for rings vs. $500 or more for rings, pistons and machining. It's cheaper, but I don't want to throw away $140 and all the labor just to find my compression bottoming out in a few thousand miles.

Any adviced appreciated.

Ace.

[SqDancerLynn1]

I have done a few V-8 engine rebuilds NEVER had any luck just putting in rings

[duaneage]

If you can get the dimensions correct it may be OK.

You need proper psiton to bore clearance
You need proper ring end gap, determined by testfitting rings in the bore.
Pistons should be cleaned properly and have the ring to groove clearance verified.
If the taper on the bores do not exceed specs, and the bores are cylindrical, and you can get a proper crosshatch pattern on the walls without removing too much metal ,

I say go for it. Boring an engine oversize involves all of the above anyway the only difference is the slugs are bigger. And if a stock set of jugs are bored over on a machine, there is always the possibility that they might not be bored on center or evenly. You have to truct the machinist.

Engines that are run in are also seasoned, heat and cold cycled. if you have broken rings and the bores are still standard size then fresh rings on a properly prepared bore wil work just fine.

If the bores are opened up even a little, then after honing you might be a bit large. Hone them first as if you are assembiling the engine and see what you end up with. Oil the cylinders after you are done since they are like fresh wounds and rust will form before you very eyes if left unprotected.

[Clone]

I have rebuilt a few engines, aircooled and water cooled. If the bores are within tolerance, I would reuse them. I have mix and matched sleeves on a few VW aircooled engines with cleaned old pistons and new rings properly measured for gap. The compression on every engine has stabilized after the rings have seated and stayed up. Don't sweat using old bores, just take them to an engine rebuilder to have the bore measured for tolerance. If they are ok, just clean the pistons, re-ring and either hone the bores yourself or have a shop do them.

[flyingace]

Thanks all for the advice.

I have read that honing cylinders is counter-productive unless: 1. It follows a re-bore or 2. You use chrome rings. Does anyone know if these rings are chrome? They look shiney, but I can't tell.

And if you have a counter opinion about the honing, I'll be happy to listen.

[duaneage]

honing the cylinders creates a finish that seats the rings, even cast iron ones. The finish cuts the ring into the cylinder. usually a 45 degree angle is required for the up and down marks.

[flyingace]

Yeah, I know that's conventional wisdom. Try this:

http://www.angelfire.com/biz/snwvlly/bikes/dnthone.htm

I just hate to take any further metal off my cylinder bores if I don't have to.

Don't get me wrong, I really appreciate the advice.

[duaneage]

I don't agree, he points out three "fables"

1. Valve lapping most engines is standard procedure, The suzukis are an exception it seems because they have hardened valve faces and are specially treated.

2. Knocking the ridge off the top of the cylinder is don to prevent damage to pistons that are brough out through the top. If the piston is brought out the bottom, fine. But cutting the ridge prevents damage to the pistons. period.

3. If honing is so bad, why do so many professional engine builders , including manufacturers , bother to hone? A cylinder hone is not taking .02 off the walls, you need cutting heads for that. New rings are not perfect ( he does not bother to mention that) and the honing customizes the addressing face of the ring to the walls. That is why the clearances are supposed to be within tolerance. Pressure behine the ring and on top of the ring seats it into the bore.

Your choice, but any manual you pick up includes that as a step. But then he would have nothing to write about on the internet about.

More from his site:

http://www.webhome.idirect.com/~snidey/pm/index2.htm

And we are supposed to believe this as well?

[flyingace]

I've done some other reading as well. The point of 'roughing up' the cylinder walls is to retain some oil in the miroscopic valleys. This aids in ring lube and breakin. I couldn't find the SAE research he referred to, so his credability leaves a lot to be desired. It makes me suspicious when a guy constantly sez 'I don't care if you listen to me or not'.

My manual instructs to hone the cylinders, so I am.

Thanks,
Ace.

[Pete's GS]

I wouldn't fool around with old rings and pistons in a mix-and-match hope that it might all work. I'd just go up a size on new pistons and rings. Better, I'd spring for a big-bore kit. We all weight the expense and benefit or keeping an old bike going, but if you like it, it's still cheaper than anything new. And it's unique.

[flyingace]

This would be new rings. I've measured the old rings, and they are by and large worn beyond the end-gap limit. The bores are hardly worn at all, and by mixing/matching pistons and bores, I can get a good piston/bore fits within tolerance.

What I'm trying to determine is if using worn pistons from other cylinders will cause unforseen problems - even if they seem to fit OK.

[duaneage]

This would be new rings. I've measured the old rings, and they are by and large worn beyond the end-gap limit. The bores are hardly worn at all, and by mixing/matching pistons and bores, I can get a good piston/bore fits within tolerance.

What I'm trying to determine is if using worn pistons from other cylinders will cause unforseen problems - even if they seem to fit OK.

Again it comes down to measurements and condition. Upon removal clean down to the metal all your pistons, inspect thoroughly for cracks and wear, and then measure everything. Use the same ring if you can on all the pistons to measure ring-land distance and then you can accurately compare pistons. Careful not to break the ring or cut yourself doing it.

Keep a chart of each pistons measurements and make your decisions. There is not bad karma or mojo, if they fit they fit.

[Eliseo Monteverde]

Ace;

I am in the same situation like you at this moment with my kat 650.
Please, keep me informated about your work in your engine.
Thanks.

[Smooth Operator]

Classic cylinder honing works to establish surface finish as well as dimensional truing. Surface finish is critical to not only allow oil retention, but to break up the hydrodynamic oil film boundary that can keep ring faces from making proper cylinder wall contact. In other words, the microscopic ?scratches? give the oil a place to go, much like tire tread gives rain water a place to go. The oil retained in the ?scratches? is then released in a controlled fashion to maintain a ?thin film? lubrication boundary, ideally a single molecule thick.

This thin film boundary allows the high points on the ring faces and cylinder surfaces to ?wear? down and form a metal to metal fit capable of sealing high pressure hot combustion gasses. If this oil film gets thick enough to let the ring faces ?hydroplane?, those surfaces won?t wear in (break in), hot gases can escape passed the ring faces, over heating them, AND those faces wont have intimate enough cylinder wall contact to adequately give up their heat to the cylinder wall? result: collapse?

In order for this ring face to cylinder wall metal to metal fit to seal high pressure combustion gasses, this fit MUST be very close. Ideally, closer than the width of a nitrogen molecule. Cylinder honing helps make the cylinder both round and straight. The classic 45 degree cross hatch not only establishes useful surface finish oil retention channels, but also assures the hone has exactly the same axial and radial motion. This, assures the hone has a chance to simultaneously correct taper and ?out of round?.

It also helps keep stone wear even.

Out of round cylinders leave gaps that rings must wear to fill. Tapered cylinders work the rings in and out, accelerating ring land wear and possibly fatiguing the rings.

Most of cylinder wear will be due to the top ring and causes the wear ridge. Wearing this ridge rounds the top edge of the ring to match. If you put a new ring against a previously worn ridge, it won?t have a rounded edge to match and will cause accelerated wear.

If you can measure a ridge, cut it out. Make sure the cylinders are reasonably round and straight, get the surface finish to specs and you?ll have no problems with them. Be sure to check ring grooves for taper.

Nothing can beat a GOOD bore job, but you always run a risk that it could get fouled up. These used cylinders were running and are proven quantities.

Careful with honing. It can leave grit embedded into the cylinder wall surface and cause wear that won?t be obvious for 50,000 miles? Since solvents are virtually the same weight as the honing oil, they can?t get under and lift grit the way old fashioned soap and water can. We pressure wash our honed cylinders, blow dry and IMMEDIATELY oil them to prevent rust. Be careful with oiled cylinders, or parts in general, as oil will collect dust from the air? wash, oil and assemble?

[Doctor Shifty]

This would be new rings. I've measured the old rings, and they are by and large worn beyond the end-gap limit. The bores are hardly worn at all, and by mixing/matching pistons and bores, I can get a good piston/bore fits within tolerance.

What I'm trying to determine is if using worn pistons from other cylinders will cause unforseen problems - even if they seem to fit OK.

I had to do a top end rebuild on my 1981 GS1000G two or three years ago. The damage to one cylinder by a melting piston was beyond repair so the barrels needed replacement.

I got another motor from a friend, used his barrels and one piston, then used new genuine Suzuki rings. I had the "new" barrels honed, even though the original honing marks were still visible and there was no ring step at the top. The honing was merely to set the surfaces up for bedding in new rings.

The mechanic/engineer who did the work was a V8 racing motor dude who already knew the measurements of my motor. He saw no problem with using the original pistons from my motor in the replacement barrels, as long as the ring gap was set up properly.

The motor went back together easy and I'm still riding it with no problem. It pulls like crazy when I wind it up, which prevents me from taking notice of my mates who reckon I should update to a newer bike.

Kim