Hi, I just bought a 91 600f2 with r6 fairings that the guy couldn't get running. Come to find out after tearing it down I saw no signs of an air cleaner and best cylinder compression is about 30 psi only after some wd-40 treatment. I pulled the head and I need to bore the cylinders. The head, cams, cam bearings look great. Valves look fine too. 24k on motor.

I found and downloaded the factory service manual. It lacks info on bore sizes, piston/ring replacement, compression specs, etc. I measured my bores out to 65mm so they are still factory bore.

I spent about 2 hrs searching for info on boring these blocks. About the only thing I came up with was wiesco piston/ring kits $500-$600. Screw that, I can buy a f3 motor with 9k for $450.

My questions are:
How much can I bore the block and retain the stock pistons with new rings?
Where do I purchase pistons/rings for these motors that isn't going to cost and arm/leg?

Reason I'm willing to rebuild it is that I have access to 2 different machine shops so I can get it done for cheap. Just need cheap parts!

Thanks for the help/suggestions!

 

My questions are:
How much can I bore the block and retain the stock pistons with new rings?
Where do I purchase pistons/rings for these motors that isn't going to cost and arm/leg?

You can't bore it at all and use the same rings and/or pistons.
The best you can hope for is to HONE the barrels, which doesn't take off enough of the barrels to require new pistons.Probably .005 " is what honing will remove.
try www.mrcycles.com
or
www.bikebandit.com
for spares.

 

Ok, found some rings for pretty cheap on bikebandit.com .

Why isn't there any ring specs in the service manuals? All they show is how to remove and install them.

There doesn't appear to be any deep gouges in the cylinder walls... so that's good. Maybe honing will clean it up. I have 2/4 pistons out, then ate some dinner, so now i'll head back out to the shop. I'll pull the other pistons and see how much I can cleanup the walls with the hone.

I flipped the head and filled the chambers with wd-40 NO leakage in 2 hrs (of course with no cams in. Also double checked that the cam sprockets were previously installed correctly to reassure me that when I had checked the timing it was right. (as I have no idea who has done what on this motor).

 

those rings must have been wicked roasted for your compression to be that low. Head gasket? Bad rod bearings? Bent connecting rod? I donno man. You should be able to see a 30PSI cylinder when you look at it, if ring-to-bore seal is the known offender.

 

I know, I'm with you. Sounds crazy. I pulled all the pistons last night. #1 & #4 rings were stuck. I could pull those 2 from the block and simply reinstall them without a ring compressor (just as an example... I didn't reinstall them like that). So, that explains those two cylinders. The walls on those cylinders still had factory cross patterns showing and the bores were smooth.

#2 & #3 rings were not stuck. Those bores showed no signs of cross pattern. I honed the crap out of all the cylinders, and I'm going to order new std rings and see what happens.

Head didn't leak wd-40 upside down for 5 hrs. Headgasket looked perfect, very slight wear on rod bearings. Rods looked straight as arrows.

 

what type of hone did you use?

 

3 jaw stone hone. There has to be something else wrong than rings....Honing them certainly won't hurt... I'm beginning to wonder if someone tried to swap in cams from something else. The more I work on this engine the more confused I become

i put the pistons back in after freeing all the rings to look for another problem. Put the head on, timed the cams. Still have no compression. I can VISUALLY see where the compression stroke is by making sure both lobes are pointed up and piston is coming up. If I put compressed air to a cylinder that is on compression stroke the air leaks out of the intake ports. Ok so that would mean that the intake valves aren't seating properly but Because earlier today I had the head off, put both cams back in, flipped the head and filled each one with wd40 on each cylinder in it's respective compression stroke (by rolling the cams). Not one cylinder leaked a drop of wd-40 in the 30 mins I let each one sit before checking the next.

I'm lost.

 

You did nothing with that hone, if you suspect that a good honing might help. These are Nikasil plated-bore motors. The bores are plated with a ceramic suspended in a nickel metal matrix, to make them extra tough. Since they are extra tough, they can't be cut with standard abrasives. The only way to hone a Nikasil motor is with a diamond hone, which few have the pleasure of owning. I don't. I just clean them and make sure they look good, as many manufacturers recommend. If there is scoring in the bore or irregularities, it's just kinda over. New engine/re-plate time.

Honing Nikasil bores with a stone hone just gets little bits of the stone hone stuck in the existing hone pattern of the bore, and knocks down the micro "ridges" on the factory crosshatching pattern that would have otherwise assisted in the proper break-in of your engine.

That valve leakage thing is funky. If the head passed the kerosene/WD test with flying colors and you can HEAR air leaking, something is mechanically fishy. Did the buckets ever come out for any type of inspection you did? I can't think of any other reason. I would say that clearances were wrong and the cam was holding the valve cracked open just a bit, but you checked that.

 

Man, these engines sound tough ! I'll ask my machinist friend if he has a diamond hone. He seems to have every thing else!

I have narrowed the problem down to the intake valves. Pulled them all and they have a double angle in them. Exhaust valves are straight 45 deg cut. So I'm going to assume that the intake valves are shot. I even put the head back on and left the cams out and hit it with comp air to make sure that the cam wasn't holding them open. Still leak a lot. Seat look fine too. Again, I have no idea what was done to this motor... I can only imagine.

I can get a used head with valves and cams for about $100 so I'm going to go that route, unless I can't find the right hone.

Thanks for the clarification on those bores. I had no idea they were that hard!

 

careful with that hone, now. Nikasil isn't particularly thick...