1971 BMW r75/5 SWB--which pistons & rings do I order?

[151henry151]

Hey there,

I'm about to order pistons and rings for my r75--I was looking here http://www.bmwhucky.com/007511.html
But I wasn't sure if I needed the 82.475 or the 82.485, or what those numbers refer to.
Furthermore I was wondering if there is any cheaper place to buy them, or any other suggestions.

Thanks,

Henry

[Garnet]

Those numbers refer to the size of the piston. Since you are boreing the cylinders it does not mater as the machine shop will bore to the size of piston that you have.

I would very seriously consider these: http://www.motoren-israel.com/product_i ... -St--.html

Remeber to take the German VAT out of the price. That makes them just under 302E which is a bit under $400.

[Garnet]

If you are on a budget, check out http://www.motobins.co.uk/bmw-parts.php and look up 50110 pistons to fit an R80/7. They are 9.2/1 comp and the R75 cylinders can be bored to fit. They will be about $260ish for a pair. And you will pick up 3 or 4 hp.


PS: I have a set of KS pistons from Huckey's in one of my R75 engines, and they are top quality and Hans is a pleasure to do business with.

[151henry151]

Thanks for the helpful replies.

Anybody know where I can get a set of jugs for this bike, and how much they would go for? In order to avoid boring the cylinders.

Basically, the bike has no compression (35 psi on the left, 75 on the right) and I want to fix it for as little as possible. I'm assuming pistons rings and a valve adjustment will do it. Any advice?

Thanks

Also, I have done business with Hucky's parts in the past and also found it was a pleasure, that's why I looked the parts up there.

[Duane Ausherman]

I would first suspect the valves and seats to be responsible for the low compression, not the rings and pistons.

[151henry151]

Duane! I remember you were most helpful back when I was figuring out my front end wobble, if my memory serves me...

I spoke with a guy at a shop in Red Hook in Brooklyn called Moto Borgotaro (he mostly builds custom cafe racers out of old BMW's) and he tried to start my bike for about 45 minutes (rebuilt the carbs, adjusted the points, put a new battery in it) and his assessment was that I needed rings and pistons. I'm not sure how he came to that conclusion, other than the compression test. However, I'm about to have the bike in a shop where I can do my own work on it for a while, so I'll find out shortly whether it's just the valves or if he was correct.

[bbelk]

Duane! I remember you were most helpful back when I was figuring out my front end wobble, if my memory serves me...

Yes - that would be Duane, he is all about wobble. I also agree that you should start with valves. Unless you see scoring I would try that first.

[Major Softie]

A compression test tells you if your compression is bad, but not why. A leakdown test can tell you why a motor has poor compression.

[George Ryals]

Leak down test tells you why, IF you know how to listen to your engine while it is being tested.

[Major Softie]

Leak down test tells you why, IF you know how to listen to your engine while it is being tested.

Anything that tells you anything requires you to know how to listen if you're going to get the message.