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Clearence when reboring cylinders
- malmac
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Clearence when reboring cylinders
What clearence do you allow between new pistons and the bore.
I have measured the clearence between new standard R69s pistons and new %69s barrels (thank you Ulis) and the clearence is .03mm.
So that is based on the diameter, so .015 when the piston is central to the bore.
In the workshop manual it talks about Piston Skirt clearence for R69s being .08mm+.1mm.
Seems like .03 is a tight fit?
Any insights would be appreciated.
Mal
Toowoomba- Australia
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Piston clearance
I remember from my Motocross days that I was always told that air cooled engines need a tighter fit to transfer heat. I'd like to explain why I did this work. I bought the R69S engine several years ago by itself and really had no history of its former life. I bought this engine to use in my R67/2. The engine worked perfect for the 2000 miles I rode it last year. When out for a ride a friend told me that that engine was smoking a little under acceleration. So this winter I took the engine apart and discovered that one piston was standard size and the other was first over. At that time the piston clearance was at .006". That was nearing a point when it was time to have this work done. I'm told that back then it wasn't unusual to repair one cylinder and leave the other side. Again the engine ran perfect and was very smooth, so it didn't seem to affect anything. I had the cylinders bored to second over. The engine is finished and once again it works perfect and runs smooth. I have only put on 25 miles so far.
Regards, Michael
- malmac
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so was this measured at the piston skirt
Was the clearance measured at the skirt of the piston on the thrust side?
At the first measurement I only had "002" thou between skirt and barrel. That all seemed a bit tight to my liking but Ulis supplied both the pistons and the new barrels so I guess I had better remeasure and confirm before I contact them to ask.
Looking like an idiot is an easy task unfortunately, so had better try and get all the numbers right before I contact them.
Thanks again
Mal
Toowoomba- Australia
- malmac
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Thank you for your reply
Mine has been worked over and I am not sure which parts have been changed but some definitely have.
The timing gears dont match, the flywheel has been skimmed for clearence and it looks like the valve lifting bores have been resleeved.
So it is time for some tender loving care.
Thank you for sharing your experience. My pistons are also from Ulis.
I had better go back and remeasure the clearence and see if I have mis read the guages.
I have a set of internal micrometers but not a dial style bore guage.
Thanks again
Mal
Toowoomba- Australia
- schrader7032
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Quote: .0030" for "Solo use"
Which is it? 0.762mm is 0.03"..0030" for "Solo use" or .762mm.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
I used benchmarkworks :
92 R100RT/69 R69S
2004 Aprilia Atlantic 500cc single cylinder Scooter
83 Honda V65 Magna, fastest production bike in1983
2015 Can Am Spider SE6 1,688 miles
2018 Moto Guzzi V711 Special
- schrader7032
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OK, in your first post, you
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
- malmac
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the page out of the official BMW workshop manual
here is the page out of the original BMW workshop manual.
I assume that the R69s clearence is higher than the the R50 and R60 because it was anticipated the S would be ridden harder and have more piston expansion. But maybe the pistons, with the high dome were manufactured differently and had a larger mass to expand.
Anyone with better information?
Mal
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Toowoomba- Australia
I set my R69S to Bench Mark
92 R100RT/69 R69S
2004 Aprilia Atlantic 500cc single cylinder Scooter
83 Honda V65 Magna, fastest production bike in1983
2015 Can Am Spider SE6 1,688 miles
2018 Moto Guzzi V711 Special
https://w6rec.com/duane/bmw/p
Malmac Here is some information on the /2 pistons. Don't know if will help or not...but.
92 R100RT/69 R69S
2004 Aprilia Atlantic 500cc single cylinder Scooter
83 Honda V65 Magna, fastest production bike in1983
2015 Can Am Spider SE6 1,688 miles
2018 Moto Guzzi V711 Special