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Old 10-06-2012, 01:36 PM   #1085
Box'a'bits OP
In need of repair
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Joined: Sep 2008
Location: Wellington, New Zealand
Oddometer: 2,393
Re- Ringing & Fitting Higher Compresssion Pistons:

RS 9.5:1 pistons after cleaning

RHS head after cleaning

Top (left) & middle (right) compression rings. The old ones are in the background. Used the piston to push them through the bore.

Oil scraper ring. The old one is in the background

All the new rings measured in a 0.5833mm - larger than end spec 0.5mm. But way smaller than the old ring gaps.

LHS, top & middle compression rings. The old ones in the background. Ring gap 0.533mm. Slightly less on the left side, probably because that’s where the breather tends to vent the most.

All back together now. & the rings are bedded in. I wound the motor over with the beancan & coil disconnected, & the plugs out, to get oil around & up into the top end. When things were reconnected it was a slow initial start given the dry bores & bosch starter motor.

The miss is still there.

More timing info:
From Snowbum
"BMW made some initial changes as the cleaner emissions models were contemplated. One change was the BMW changed the CAMSHAFT sprocket by THREE degrees; this is same as SIX degrees measured at the crankshaft, as far as valve timing is concerned. BMW changed ONE flywheel marking, by repositioning it, when the three degree change in camshaft timing was done. The NEW timing point was placed 6° BEFORE the original marking, as seen in the direction of the moving flywheel. That was 12.5 mm on the flywheel, in the direction OF THE TDC (OT) MARK. NOTE that the STATIC ignition timing (also called idle timing, or the S mark) was NOT changed, it remained at 9° BTDC. Obviously, OT, top dead center marking, also was not changed. Think about the differences of no-change at S, and a 6° change at the maximum advance point. ((For the super nerdy, yes, if you have a wrong flywheel, or just want to know, you can measure the S mark and see which flywheel you have))"

The change was made in the positioning of the keyway on the cam shaft sprocket. Effectively for emissions. The change happened in 01/78.

Takes a little thinking through..
  • Late ignition (post mid '78) S = 9 degrees BTDC, based on 25 degrees total advance Z = 34 degrees BTDC.
  • Lines around the S mark are +/- 3 degrees. Originally to give indicators for acceptable wear limits for the timing chain (mirror imaging)

Late ignition change is said (Snowbum) to be for emissions reasons.

Currently running Gus at 6 degrees ie pre '78 'S' mark less 3 degrees = the line prior to the S Mark. BUT the full advance is happening at the 'F' mark. This on both the available beancans. So probably okay, & ruled out as the cause of the miss (I have already experimented to rule this out).

Currently on 1.25 turns Idle Mixture Screw, 2.73 Needle Jet, 3rd clip down from the top of the Jet Needle, 150 Main Jet. Slightly too rich, & has a tendency not to engine brake. I'll go back down to 2.70 or 2.68 Needle Jet.

I've won some SV1000 exhaust pipes on Trade Me cheap + postage. Intent is to get a mid pipe made up to fit, as well as a front balance pipe made to fit the headers (like stock). I'll also get some bungs made up to allow an Air Fuel meter to be fitted. That'll help resolve the jetting issues. Anyone want a right side pipe? I only need the left of the pair.

Zeta Fuel Tank Breather:
Discovered this works whatever orientation it's on. The BMW Fuel Cap I got a while ago has a horizontal vent, with a view towards the breather hose being fed down the steering stem. I never got around to doing that, & on the Makara ride I ended up with fuel pissing out when Gus went over. This should resolve this. The one issue may be whether rain can get in (but this has to be better than what I had). I think the prior chrome cap obviously vented via the key aperture, so that also could have caused issues.

Originally Posted by Padmei View Post
You know how the internet is- full of doom etc. There's been old hands that don't like the left over soda getting into places it shouldn't, However when even my local mech was concerned about it I thought it best to live with the patina.

Nutso i also subscribe to your idealogy. I call it the ostrich protocol.
Soda blasting is okay. You can just wash it out. Its water soluble. It is media blasting (bead/ glass / walnut / sand etc) that is of concern.
My '91 R100GS thread is here
My Ride photos are here

It's just better when there's twins involved....

Box'a'bits screwed with this post 10-27-2012 at 11:13 PM Reason: Updated as I try to work thru' issues
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