How far can I go?

[oldktmdude]

My 1100 has low compression in all cylinders due to worn rings and bores. How far can the original 1100 sleeves be bored to, safely? Are Wiseco 3mm oversize piston kits a good way to go? Are there any problems associated with using these big bore kits, eg overheating, tuning etc.
Regards, Peter.

[SlowOldGuy]

What are the comperssion numbers?
Did you hold the throttle Wide Open when checking the compression?

Wiseco offers a 3mm overbore in 10.25:1 compression ratio that works without any extra machining (other than the overbore).

DavidR.

[oldktmdude]

G'day DavidR, the comp numbers were as follows, 1 - 95 psi, the other 3 were all around 105 psi. Throttles were held open during testing. Even with oil added to cylinders compression only increased to around 125 psi. The wiseco 3mm kit seems like a good way to go. Regards, Peter.

[ren-dog]

Yamaha supplies an 1100 piston @ 0.5mm oversize. $ Add rings, gudgeon pin clips and machine work.
The wiseco kit, K1188, appears 2B the largest kit for an 1100 crankcase. $ Add machine work.
As my granny used to say ... Nothing a dose of Epsom salts won't fix 

[Pat Conlon]

Hey Peter, nothing to add which has not already been posted. Wiseco's the way to go...
Pardon a few follow up questions: Are your valves adjusted to spec?  My compression #'s went up when I did my valves. Have you thought about doing a leakdown?
How many miles on the motor? Any symptoms? Burn oil? Lots of blow by?
Randy @ RPM has mentioned that he has found in some cases, Yamaha's cylinders has been a tad out of round (or something like that)
With new pistons, it would be a good time to check that out.....Randy?  
Cheers!

G'day DavidR, the comp numbers were as follows, 1 - 95 psi, the other 3 were all around 105 psi. Throttles were held open during testing. Even with oil added to cylinders compression only increased to around 125 psi. The wiseco 3mm kit seems like a good way to go. Regards, Peter.

[oldktmdude]

G'day Pat, thanks for your input. I'm unsure of exact milage the bike has done as I'm not the original owner and am unaware of the bikes history. The speedo is reading 17,000 kms but I'd say that means 117,000 kms. (around 75,000 miles) The valve clearances were checked about 500kms (300 miles) ago and were all in spec. It uses a little oil and I've been told by riders following me, that sometimes it blows a little smoke under hard acceleration. I think it's due for a rebuild so i'll have a good look around when I pull it down. Regards, Peter.

[andyb]

Measure carefully before you start ordering stuff, you may be able to get away with just rings and a little work.  Pistons and more displacement would sure make it quicker though.

[racerrad8]

Randy @ RPM has mentioned that he has found in some cases, Yamaha's cylinders has been a tad out of round (or something like that)
With new pistons, it would be a good time to check that out.....Randy?  
Cheers!

G'day DavidR, the comp numbers were as follows, 1 - 95 psi, the other 3 were all around 105 psi. Throttles were held open during testing. Even with oil added to cylinders compression only increased to around 125 psi. The wiseco 3mm kit seems like a good way to go. Regards, Peter.

The cylinder sleeves are honed prior to being installed into the barrel. Once the aluminum barrel heat cycles, it distorts and thus creating an out-of-round condition. If going to a larger piston boring and honing will be required so that will take care of that issue.

With the compression numbers being so low and the oil not helping that much, you also need to look at valve condition. The oil will not affect the valve sealing and that is why the oil did not make a significant jump.

Unfortunately, the current cost of Wiseco pistons has made the Yamaha piston a better and cheaper deal.

Randy - RPM

[SlowOldGuy]

With the compression numbers being so low and the oil not helping that much, you also need to look at valve condition. The oil will not affect the valve sealing and that is why the oil did not make a significant jump.
Randy - RPM

Good point, Randy.  I had forgotten about this but, the early models were known to warp their valve seats.  Even the nicely treated engines had this problem.  When I finally got around to inspecting the valves and seats on my 1100 at 16Kmiles, I had one seat warped.  The fix was a refacing or the valve seat and lapping the valve.  If the valve showed any sign of leakage or bured seal area, it needs to be replaced.  Stock Yamaha valves are surface hardened and the face can not be re-ground.  My valve looked questionable, so I replaced it. 

That first time I had all the seats re-done.  A few years ago, I replaced all the valves with SS after an inspection showed a lot of pitting on the valve face.

DavidR.