Vintage BMW Motorcycle Owners

St:
As I said my compression dropped from 160 pi. to 100 psi. rather quickly and in both cylinders. I took apart and cleaned the crankcase vent. When I did the spring flew off and brushed my forehead as it flew away. I scoured the floor and bike surfaces to no avail. I ordered one from Max, only $2.00 but it has to come from Germany. I went back out to the garage and moved everything in the area (3 bikes, 2 lawn mowers, etc). Then I swept the floor and dragged a magnet through the pile of dust. I found the missing spring clinging to the side of the magnet.

That crankcase vent is so simple I don't see how it can be the problem, as long as it is clean. I blew air into it and the air came out the dipstick hole. When I reassemble, I will blow air in the dipstick hole and see if it comes out the vent.

Craig

Forgive me Craig, I missed the part of your posts where you mentioned the compression going away from 160 to 100.

A bad habit of mine is to read these posts first thing in the morning before I have had a couple of cups of coffee and am fully awake. I apologize.

That big a drop in compression in my mind screams something major changed. You are on the right track getting the problem solved. LOL, I will keep an eye on your progress but keep my fingers off the keyboard for replies until I am sure I have read what has been posted. Cheers, St.

The valves looked almost new (see photo below(, but so did the rings. When I honed the jugs I couldn't even find a ridge. I made a ring compressor with a 4" hose clamp and a piece of 3" stove pipe so I could put the rings on without taking the rods off the crank and exposing the bearings.

I'll be down for a couple of days, but I'll post my progress when I get back to it.

Craig

i always leave the piston in the jug and just take out the wrist pin. Just take out one (1) wrist pin circlip and push out the wrist pin. Always use a NEW circlip on reassembly.
While the jug is on the bench you can push out the piston and fuss with the rings. Then it's easier to use a regular ring compressor to put the pistons back into the jugs. Some guys just use their finger strength to compress the rings one at a time.There is a chamfer on the jug.

-Randy

Did you inspect the underside of the valve seat for recession/wear?

Pete:

I did not disassemble the valves. If you read back a couple of posts you will see that I filled the inverted heads with 1k and they didn't leak any out, so I didn't see the need. The rings slid back into the jugs very smoothly with my makeshift compressor so I think I'm ok.

I had to have a minor medical procedure Friday and so haven't finished reassembly yet. I got the jugs back on and let it sit until I could get back to it.

Craig

I recall the inversion with fluid in the heads and no leak. So the seal is good, But with it apart remove the spring and check the guides and underside of the valve for wear. The last thing you want is a broken valve damaging your motor. Check snowbums site.
I wish you and your motor good Health.

Good luck! St.

Crank case seemed to work ok.

300 miles and no sign of leaking so far. (The orange color at the base of the jugs is Permatex high temperature RTV gasket sealer.)

Craig

Good show. St.