Engine upgrades 77 r100/7

[Bobby]

My 77 r100/7 ( now an RS) has close to 150000km on it, has reco gearbox and new dellortos. It runs nice and smooth, starts easy.po mentioned it has less compression on left side and blows some smoke on the left.

I need to replace the pushrod seals and was wondering while doing this if i should go for a 1 size over rebore and new pistons. Or is it a better choice spend a bit more and go the seibenrock 1000cc kit with new nikasilbarrels. Is this kit worth the extra cost compared to the rebore?
Should i be thinking og the bottom end 1st with this amount of km? Also thinking of converting the heads to run on unleaded any ideas there?
Its a bit tricky where to know to start.

Cheers,
Bob

[Kurt in S.A.]

Bob -

I was at the same spot on my '78 R100/7. I had 100K miles and I was getting more and more concerned about the valves. Although they were stable and I wasn't really having any oil use issues, I decided it was time. I pulled everything down and sent the heads off to the Beemershop...now I don't have to worry about that. I had the cylinders measured...I felt I couldn't do it accurately enough. They came back as being out of spec. I priced new BMW parts (pistons, rings, wrist pins) for a first oversize...pretty darn expensive. I've heard from some of the independent mechanics, that 1st over on the 1000cc barrels is a crap shoot. Generally, they don't remain pure oval and distort or "snake" over time. Maybe it has to do with how the rebore is done. But it seems that taking that much material out of an already thin liner is just asking for trouble.

So, I opted for the 1000cc Siebenrock it from the Beemershop. Supposedly, the CR is up to 9.5:1...I didn't want to deal with that (ie, dual plug) and felt it was too high for me. So I also bought the reducer plate...it's actually and R60/6 base plate...drops the compression ratio to about 8.8:1 which is slightly under the stock compression. The Siebenrock kit has lighter pistons and wrist pins and the cylinder is all aluminum with the Nikasil coating...it allows better heat dissipation, which is somewhat of a problem for the 1000cc engines.

I like it. I felt the difference right away, although it may be just the fresh top end that was the difference. But I'm glad I went that route. For me, it was less costly for the kit as opposed to the rebore.

I left my bottom end alone...didn't even pull the rods...maybe should have. But it appeared that I was getting good oiling so I didn't consider it an issue. Oh, I did have to replace all the cam followers...a few were pitted...that's an important thing to check if you redo the top end.

Kurt in S.A.

[Bobby]

Thanks for the reply kurt,

Ill go the kit option when i can. What did they do to the heads at the beemer shop, did they run like a new valve kit through it? I thinking of ordering the gear i want through motobins, getting the head rebuilt by a local bike mechanic ( hes an older feller with heaps of experience on older bikes) and doing the rest myself. Maybe a bit expensive to send heads off as im living out in the boonies in norway. Did the stick with stock valve sizes?

Is S.A south Aust? Im an aussie aswell.

Cheers again,
Bob

[Kurt in S.A.]

Bob -

My S.A. is San Antonio, Texas...not nearly the same as South Australia...would be nice, though! I've been to Norway, but not the boonies...just around Oslo...I really enjoyed that!

I don't remember the details of the head overhaul, but generally it was new valves and seats that were spec'd for use with unleaded gas. Ted Porter is one of the experts at Airhead head repair. It's a debated topic and I really don't know enough about head work myself, but my opinion is that someone should be very familiar with Airhead heads in order to work on them...grind angles, spring tension/height, etc. Again, I'm not speaking from that much specific knowledge, so I decided to use an expert, someone who does this type of work day in and day out. If you have someone that has done work that stands up to use, then that's half the battle.

Kurt in S.A.

[tsa]

My 77 r100/7 ( now an RS) has close to 150000km on it, has reco gearbox and new dellortos. It runs nice and smooth, starts easy.po mentioned it has less compression on left side and blows some smoke on the left.
I need to replace the pushrod seals and was wondering while doing this if i should go for a 1 size over rebore and new pistons.

If you can live with the oil leaks for the summer riding season (btw., there is a specific tool designed to seat the pushrod tubes a bit deeper, which might improve the PRT to crankcase sealing), I'd wait with taking things apart until autumn/winter, and then take a close look at what needs replacing. Unless done before, at 150 kkm, the exhaust valves should be due for replacement. Also, it would be sensible to try and figure out if the left side smoking actually is from the cylinder/piston rings or the valve guides. Only when you have things apart you can tell if you need a rebore (as mentioned not recommended for the R100) or a hone + new rings, and thus preferrably avoided), or if other things, such as worn out valve guides cause the smoking.

[Foxy]

Hi Bobby,
I am across the border from you in Victoria Aust.
I was facing similar issues to you with my 1971 R75/5. It had broken a ring. Rather than rebore and new pistons I elected to purchase the Seibenrock 1000cc kit. I also had the heads completely reconditioned locally by a very well respected engine reconditioner. This is not cheap, around $500 + parts from memory, but necessary I would think.
I have done around 6000km on bike since rebuild and I am very happy with it. It runs beautifully with all standard jetting and settings, just like they said it would. The only thing I did add was an Alphpa Classic ignition system from Munich Motorcycles in Perth, WA. These are absolutely first class ignition upgrades for early airheads.
I assembled mine with out any base gaskets, so assume it is running the 9.5 : 1 compression ratio as claimed. It doesn't feel like a high compression motor. Starts easily on origional starter motor. Still running single plug heads. Absolutely no sign of pinging/pre-ignition whatever you want to call it. I generally run it in 98 octane BP fuel, but have put plenty of 90 octane fuel through it with no noticable impact.
It has more torque and HP than before as you would expect.
Oh yeah, I forgot, I did put new big end shells in it, but I doubt it required them. I did also replace the small end (gudgeon pin) bushes. This required line boring done by the same engine reconditioner. This is expensive so dont do it unless necessary.
Also fitted a deep sump fom Seibenrock and run the origional recommended oil quantity of 2.25litres.
If you choose the kit option, have a very close inspection when it arrives. One of my cylinders was slightly smaller than the other. The pistons would slide through one cylinder (with no rings fitted) quite easily dry, the other woud need to be pushed through. Seibenrock were very unhelpfull when I pointed this out. I had my engine reconditioner measure them and he was unwilling to fit them. We sent the measurements he took to Seibenrock and their reply was "they are within limits".
We sent the cylinders off to a firm in Melbourne and had the tight one very slightly skimmed. Yes you can skim Nikosil bores, it just takes specialist equipment and people with experience operating it.
Fitted them that way and as I said very happy with it after 6000km or so.
Pretty expensive in the end but should be good for another 150,000km hopefully.
Good luck Bobby and lets know how it goes.
Cheers
Foxy

[SteveD]

Rebore verses new improved?
Both will cost.
One costs more than the other.
The job if done right lasts a long time.
One keeps things stock, one adds some improvement in function, though maybe not performance too much. Still looks stock.
Now's the time to do it...well 4 years ago would've been better 'cause the $Oz was buying 30% more then!

I say go for it, but whilst Siebenrock have been the lone replacement source, there's also Richard Moore from http://www.moorespeed.co.uk/bmw-engine in the UK who is a relatively new player and seems to get good press. After reading Siebenrock's "within specs" response and hearing Moore is a helpful fellow that can be spoken with directly, I'd be inclined to investigate further.

[Rob]

After reading Siebenrock's "within specs" response...

Yeah, that was a bit disconcerting.

One would think, for the price one pays, that Siebenrock could take a moment to slide the pistons through the cylinders before they box them up.
Perhaps this service could be requested?