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1957 R50 Recent restoration New Pistons -problem!

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schrader7032
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The value of 0.00197" appears

Post by schrader7032 »

The value of 0.00197" appears to be at the minimum of the spec.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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westeagle
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What is the ideal spec?

Post by westeagle »

What is the ideal spec?

I may go to a different shop to get the cylinders re-bored to what I guess would be the 4th-over size which is 70mm.

So my preliminary order of steps to take to solve this problem currently is:

1: rebore both cylinders to 4th over (70mm)

2: order 2 new 70mm pistons

3: change out mufflers to stock style

4: dismantle engine block; add the oil hole to the right side and do a very thorough cleaning out of oil passages

Comments or ideas on this are very welcome!
'57 R50; '73 R75/5 LWB

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schrader7032
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Malmac discussed this in this

Post by schrader7032 »

Malmac discussed this in this thread:

http://vintagebmw.org/v7/node/16121

He posted a sheet from the BMW workshop manual with various specs.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Daves79x
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Kind of Tight

Post by Daves79x »

Your cylinder/piston clearance is kind of tight and would have required very careful break-in. My '59 R50 was bored to .0020 clearance. I got away with it, there is a bit of scuffing on the left cylinder wall (as observed when removing the cylinders a couple of hundred miles on to properly seal the base gaskets). It now has 1500 miles on it and I run it fairly hard, no issues.

Something I didn't do on the R50 that I did on my R69, was to manually (with a drill and a piece of fuel line) operate the oil pump while the engine was on the bench to build oil pressure and see if I had good flow out to the cylinders (both the R50 and R69 have the right-side oil passages drilled). It took a shocking amount of time for oil to flow out the feed holes to the cylinders/heads. I did not do this on the R50 and blame that for the scuffing I saw. The engine would have to run up to 30 seconds or more for oil pressure to build from dry if you don't do this. That's enough for damage to the top end, no matter how well things are pre-lubed.

I'd maybe see how much scuffing you could get out by honing. You could go out to .0025 - .0030 clearance with no problem. One new same-size piston would fix you up then, if you could buy just one.

Sadly, you have to completely strip the engine to drill the right-side oil passage. It is a rather tedious process that creates a lot of debris that needs carefully cleaned out. I wouldn't sweat that now. These pre-/2 bikes all ran for millions of miles without the passage.

Dave
Dave

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westeagle
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Hone both sides?

Post by westeagle »

Thanks Dave & Kurt!

Dave -would you hone the Left side as well and re-use the existing Left piston and rings?


Henry
'57 R50; '73 R75/5 LWB

Daves79x
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Can't

Post by Daves79x »

Can't get a good enough look at the 'good' one to tell, but if you end up taking a few thousandths out of the other side by honing, and that gets it, you might hone a bit from the good side to give you a wider clearance for both sides. If you hone, new rings are a good idea. You don't have to get all of the scoring out of the bad cylinder, but most of it.

I can't help but note in your video that you seem to be running each gear out pretty far for a new engine. And also using quite a bit of engine braking for deceleration. I'd usually take it really easy, shift as soon as the next gear will pull without lugging, for the first 100 miles or so. Very early on you need to do a plug check to see how the carbs are. I had to raise the needles in my R50. Then very carefully sync them and get down to a proper idle. Even sitting for a few minutes with too fast an idle will overheat these.

I know it's a pain, but after 100 miles you should drop the oil and the sump cover to see how things are looking. Should be maybe a very little debris, most of it magnetic if you put a magnet in the sump. Clean all that up and run to 500 miles and do it again. There should be virtually nothing in the sump this time. If all's well, then seal the sump gasket and bolts with Ultra-Gray and you're good to go. I put up with a few drips from the sump until then since it's such a pain to clean all the sealant off until you know you're done in there. But you have a bit of work to do to get there.

Dave
Dave

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malmac
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Great idea to run the oil pump

Post by malmac »

Dave

Your idea of manually running the oil pump to fill the oil lines and to check the flow is a great idea.

Also the other comments re extended idle times and careful break in of the engine are easily forgotten in the current days when new engines are almost indestructable through careless run in.

I will have to consider just how many kicks on the kickstarter prior to turning on fuel and ignition might also get the tiny oil pump to deliver the oil out to the cylinders and main bearings?


Mal
mal - R69s
Toowoomba- Australia

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westeagle
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Break-in easy or hard?

Post by westeagle »

Break in

Don't want to blame others but:
Against my instinct, I was advised by a BMW guru I trust to ride it long and hard on the break in...

I know its a controversial subject...

The next time I will try the easy-does-it route.
'57 R50; '73 R75/5 LWB

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wa1nca
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manually running the oil pump

Post by wa1nca »

Dave

Your idea of manually running the oil pump to fill the oil lines and to check the flow is a great idea.

Also the other comments re extended idle times and careful break in of the engine are easily forgotten in the current days when new engines are almost indestructable through careless run in.

I will have to consider just how many kicks on the kickstarter prior to turning on fuel and ignition might also get the tiny oil pump to deliver the oil out to the cylinders and main bearings?

Dave
Yea I also like that that idea
Quess you have the oil pan on ,engine filled with oil,and gear for oil pump not installed so you could couple the shaft to a drill??
Also use a lot of oil on piston and cylinder when installing


Tommy

Mal
Tommy Byrnes
54 R51/3, 55 R50/Velorex 560 sidecar, 64 R27, 68 R69US, 75 R75/6
Ashfield, Ma
USA

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westeagle
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Break-in easy or hard?

Post by westeagle »

Break in

Don't want to blame others but:
Against my instinct, I was advised by a BMW guru I trust to ride it long and hard on the break in...

I know its a controversial subject...

The next time I will try the easy-does-it route.
'57 R50; '73 R75/5 LWB

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