topend rebuild

[yappo]

comes the spring i will be installing a R90/6 top end on a R60/5 motor.i had the R90 stuff redone,bored w/oversize pistons.heads gone over also.i have a rebuilt set of 32mm bings too.i've not done this before but am confident that i can.the thing that bothers me is; during assembly how much lubrication do you use on the cylinder walls when you insert the pistons w/rings.i'm assuming you lube the cylinders and rings?maybe it's not necessary,i flat dont know?i'm really concerned about the break in after assembly.i've heard so many horror stories about it that it's made me question an apparantly simple thing like;my lube query.thank's all.brian.

[20774]

On my /2 overhaul, I oiled up a rag and dropped the front and backside of the rings on the rag. I put a light amount of oil on the piston skirts. Not sure about the cylinder walls...I don't think I put anything.

Break-in has been discussed a number of times. It's owner choice, seems to be. I think the consensus is not to hold a constant RPM when you're breaking it in. Get compression on both sides of the rings to force them into the walls so they'll seat. IMO, I think the most critical time is the first 60 seconds after start. I held RPM up at about 3K. After that I threw a leg over and went for the first ride.

Drain oil fairly soon after running it in. I drained after the first 20 mile ride. Keep checking the head bolt torque to be sure things are settling in.

[yappo]

most helpful.many thanks,brian.

[skiteach]

Wipe the cyls also, never heard or worried about back side of rings. Skirts should have a wipe also.

[kstoo]

Wow, a brand new 900cc four-speed with an R60 final drive? You are gonna be doing wheelies for sure!! I think that that will be a quick bike.

[krehmkej]

Just did mine last spring.

This procedure was recommended and worked for me:

VERY LIGHT wipe of oil on skirt and bore.
Set static timing carefully
Fill with regular 10/40 oil.
Start and run at ~ 3000 rpm for 45 seconds.
Shut down, put on gear and go for a brisk 10 to 15 mile ride, varying RPM all the time, up and down through the gears. DON'T baby it!
Drain oil while hot.
Let everything cool overnight.
Replace filter and fill with 20w50 oil.
Re torque heads and oil pan.
Adjust valves.
Re-check timing, carbs, etc.

As always, YMMV.

Good luck!

[20774]

Just did mine last spring.

+1...that's what I did to a tee...:thumb

[benway]

did you change the 60/5 cam?

http://bmwmotorcycletech.info/cams.htm

they have pretty different timing to the /6 900cc motor

[yappo]

i have a R90/6 cam but was thinking to just go with R60/5 setup.i see you mention that if i go with the R60 cam,the timing will be different.is this a cause for alarm?can the timing still be dialed in so that it performs OK?whats your thought?thanks,brian.

[benway]

to clarify, its the valve timing that changes with the diiferent cams, so its fixed, to that cam

obviously the ign timing will be dependent on the cam used also, but is variable.

I suspect that the 900cc top end will perform "better" or "as designed" with the matched /6 cam.

iirc people have run the 60/ cam with 750 and 900 cc top ends and it results in a very different torque curve/performance

you may also need to check for oil pump key compatability with a later cam. :dunno

it may well behoove you to join/post on the micapeak airheads list or boxerworks for more info on this. :type

hope that helps

[yappo]

thanks benway for your info.i will also follow up on those two sources you mentioned.

[8ninety8]

If you can possibly spring the cash with the engine apart, get a sport cam #336. I ordered one in 1987 from Capital for my R90S/'74, had to wait all summer as, apparently, they are ground in Germany after a number of orders are in hand. (I can't believe that was 22 years ago already!)

I think the 336 has more overlap thus allowing regular compression with lower cylinderhead pressures. I can still make the engine ping on a hot day if I really wack the throttle in high gear. But, as we all know, we have to take it easy on the equipment when away from home.

I'm looking at the receipt and I can't believe I paid $110.95 for the cam. I don't know if they are available today. I was thinking Andrews, but a former BMW mechanic said no way Jose.

That's all know about cams except that I had a R60/5 LB, and that thing pinged like a wind chime, and I defer to any correction of what I've posted concerning the 336. Time for a beer.

I only rode the 90S one time before tearing it down and putting in the new cam, and I love winding it out early in the morning. I've missed second to third more than once, and the engine revs right past redline. Scary but everything stays together.

[benway]

you're welcome

now let me go log in over there, so I can contradict myself :fight


:rofl :rofl

thanks benway for your info.i will also follow up on those two sources you mentioned.

[benway]

afaik, iirc etc

there are pros and cons to the 336 cam

the pros come with using higher compression.

the cons are there may be issues with clearance, because of the different timing and profiles, and the increased stress on a /5 crankcase, which is not as strong as the /6.





If you can possibly spring the cash with the engine apart, get a sport cam #336. I ordered one in 1987 from Capital for my R90S/'74, had to wait all summer as, apparently, they are ground in Germany after a number of orders are in hand. (I can't believe that was 22 years ago already!)

I think the 336 has more overlap thus allowing regular compression with lower cylinderhead pressures. I can still make the engine ping on a hot day if I really wack the throttle in high gear. But, as we all know, we have to take it easy on the equipment when away from home.

I'm looking at the receipt and I can't believe I paid $110.95 for the cam. I don't know if they are available today. I was thinking Andrews, but a former BMW mechanic said no way Jose.

That's all know about cams except that I had a R60/5 LB, and that thing pinged like a wind chime, and I defer to any correction of what I've posted concerning the 336. Time for a beer.

I only rode the 90S one time before tearing it down and putting in the new cam, and I love winding it out early in the morning. I've missed second to third more than once, and the engine revs right past redline. Scary but everything stays together.