Top end Rebuilding?

[TZOLK]

Who has had it done and when do you think it is necessary?
When our valve clearence become increasingly out of spec?
Who hasnt had them done and how many miles do you have on it?

[bikerfish1100]

last time i did a airhead top-end (outer-end?) was at about 50K, due to some oil weepage issues. honed cylinders, new rings & wrist pins (figured that while i was there i would drop in the light luftmeister ones. it was a while ago). left the valves & guides alone.
if you can't keep your valves in adjustment, you probably need new seats and guides. worth doing. easy job, just farm out the technical stuff to a machine shop, but do the manual labor (r&r jugs & heads) yourself.
typical mileage for a top end is anywhere between 50K and 150K, depending upon how hard you've been running it. i ran mine hard. ymmv.

[James.A]

2, R75/5's. Both over 70K. Both run just fine. The one with the lower mileage is actually a wee bit valve lash sensitive. Not troublesome though. As long as I don't flog it hard over 80mph, all it wants to do is run.

[rocketman]

Another thing to consider is that as the timing chain wears it becomes harder to keep the valves adjusted once the chain tensioner can no longer take up the slack, also makes for more noise. When that happens the rocker clearance can change as you go from accel to decel and back. The ON had some recent articles on doing that as well. Around 50-60K is generally about the it should be due for a change out. At 70K plus on both my airheads I figure its time for rings and valve job.

RM

[TZOLK]

So have you replaced your timing chain? I thought that article was geared more toward the older airheads with the different style chain than the '90s types. What years are yours? The trans is the other thing that worrys me but its still kickin.

[flash412]

Another thing to consider is that as the timing chain wears it becomes harder to keep the valves adjusted once the chain tensioner can no longer take up the slack, also makes for more noise. When that happens the rocker clearance can change as you go from accel to decel and back.Please explain how slop in the timing chain can (temporarily) alter the maximum valve clearances. The timing chain connects the crank to the cam and has nothing to do with connecting the cam to the valves. I can see how a sloppy timing chain would alter the valve timing ever so slightly; but not the valve clearances. Please explain this phenomenon. Thank you.

[TZOLK]

Flash is correct. The clearence between the cam lobes and the pushrod assembly is a regular given distance based on set valve clearences at TDCC.
A sloppy chain would only alter timing, make it hunt at idle and on accel decel maybe. Im thinkin thats what he meant,or not.

[dlearl476]

Flash is indeed correct, but in my experience having a worn chain made it much harder to adjust the valve clearance. I can only imagine that due to the slop, I wasn't getting the cam to the very bottom of the lobe consistently. I did this without benefit of a test gauge. I did it five times and never got consistent results. OTOH, I did it right the first time* after I replaced my timing chain and had Bob's install unleaded valve seats/ do a valve job.
I did this at 60K on my R60/5 but my R75/5 with the same milage shows no signs of it needing to be done. (But then it was originally owned by an Air Force jet mechanic, so it might have been done long ago)

*This was also the sixth time I'd done it, so maybe I just got a clue!

[boofer]

On my 1975 R90/6 the valves were changed over to no lead at 210k after a billion bottles of lead additive. It had earlier had the compression dropped with extra base gaskets . Took the heads and barrels into the dealer (you could still see hash marks in barrels) and said; give her what she needs.

I intended on going back to a higher compression and was worried about a ridge at bottom of stroke.They figured a bore and oversized pistons and rings at that mileage. When the heads were finished and I picked them up they said even the rings were good. For $80 I surely replaced them anyway.

This bike has had the valves adj. religously at 2k even if I had to pull on the shoulder (many a time -10 min job) and never been to a dealer, ever. I replaced the clutch at the same time (acting up - first replacement by the way) and found it to be .004 less than new spec. The activation rod was spinning with bearing and drilling a hole in pressure plate.

These things will run forever with good care, and carefull inspection!!

Sorry, toooooo much coffee today ?? What was this thread about ?

[boofer]

Right; cam lobes are excentric and when you are at TDC it's obvious just looking at the rocker arms, a bit this way or that shouldn't matter. When the timing chain gets some wear you will know, because proper dwell angle will make timing neary impossible without resetting points other than spec.

Remember - changing dwell changes timing - changing timing, dwell remains the same!

[lkchris]

Remember - changing dwell changes timing - changing timing, dwell remains the same!

This is misleading. Not of much use, either.

Dwell, of course is just the point gap, and it is always set to the specified clearance.

If the clearance changes due to wear, the solution is new points--NOT a timing change to compensate.

Setting timing is a one-time, set-and-forget operation. Do it with new points installed.

If timing changes due to wear in components, fix the wear. Treat disease, not symptoms.

In the automotive world, much like "checking wheel alignment," "checking timing" is a scam.

Believe me, if the bolts/screws that keep timing set come loose, it isn't going to move "just a little bit." It's going to move so much your engine won't run, and you'll obviously know something is wrong.

[flash412]

This is misleading. Not of much use, either. Dwell, of course is just the point gap, and it is always set to the specified clearance. If the clearance changes due to wear, the solution is new points--NOT a timing change to compensate. Setting timing is a one-time, set-and-forget operation. Do it with new points installed. If timing changes due to wear in components, fix the wear. Treat disease, not symptoms.An interesting perspective.

In my experience the rubbing block on the points wears from... rubbing. (Go figure.) Back when I was riding LOTS of miles on my /5, I used to put a small dot of lube on the point felt, reset the point gap and then set the timing every... I forget... 6000 miles(?), per the very useful owners manual. As long as the faces of the points were good, I would only replace them when the rubbing block wore down to where gap and timing could not be set.

Furthermore, the "peak" and "pit" on the point faces, which is the other reason to replace points, are actually caused by the condensor. Once you find a good condensor that doesn't let the points develop those peaks and pits... KEEP USING IT. Do not replace that condensor until the points tell you that it is worn out.

Sometimes I would get 18000 miles from a set of points before they wore out and 24k (or more, I forget) from a condensor.

[grasslander]

Furthermore, the "peak" and "pit" on the point faces, which is the other reason to replace points, are actually caused by the condensor. Once you find a good condensor that doesn't let the points develop those peaks and pits... KEEP USING IT. Do not replace that condensor until the points tell you that it is worn out.


Exactly as my dad (God rest his soul) the 40 year experienced mechanic and builder use to say...

[rocketman]

Please explain how slop in the timing chain can (temporarily) alter the maximum valve clearances. The timing chain connects the crank to the cam and has nothing to do with connecting the cam to the valves. I can see how a sloppy timing chain would alter the valve timing ever so slightly; but not the valve clearances. Please explain this phenomenon. Thank you.
You're right it should have been timing, not clearance.

RM

[pmdave]

In my experience, the less the displacement, the less the problem with valves. The R100 heads use essentially the same casting as the R75, and then the R100 casting is reduced even more by machining bigger holes. The result is that there is less metal to conduct heat from the exhaust valve area.

If you run an R100 hard, those exhaust valves and seats get awfully hot. (say, dragging a sidecar around at superslab speeds pulling upgrades against a headwind, trying to stay out of the way of the trucks) The (old style) cast iron valve seats would simply disappear rapidly, decreasing valve stem clearance. When the valve clearance goes away, that lifts the valve open, and the hot gasses go squirting past the contact area, REALLY speeding up the "erosion".

And, as the valve/seat contact surface wears, it gets wider and wider, which reduces the contact pressure and promotes faster erosion. So, one reason to have a valve job is to recut the seats to get the contact area back to normal width, even if you don't need new valves.

The symptom of tight valves is, after a high speed run, you pull into town, slow down, and the engine stalls. That, and the rocker arm ticking goes away. On long trips, I'd typically have to adjust the valves every 1,500 to 2,000 miles.

After a few trips (over two or three years) and numerous valve adjustments, there comes a time when compression just isn't what it should be, and it's time to do a valve job. It might be 60,000 miles of easy use, or 30,000 miles of WFO. I usually have two or three spare heads around, at least one with a fresh valve job. It's only an hour or so to swap heads.

The latest valves and seats are more durable, and the valve angle has been changed from 45 to 30 degrees, which seems to help resist seat erosion. With adjustments on a regular schedule, the later valves and seats seem to survive about twice as long as the older ones.

A valve job on an airhead is simple and uncomplicated. You shouldn't worry about the valves if it's running good at idle and you can hear the clack of the rocker arms on both jugs. But if it's getting hard starting, or won't idle, or compression is down, yank those babies off and send 'em to the head shop. Unless there's some reason to suspect ring wear, you probably won't need to get any deeper into the engine.

When setting the valves, the current recommendation is .006 IN and .008 EX after torquing the holddown nuts. However, some folks like to run them a little tighter, more like the original spec, at .005 and .007. The increased clearance doesn't make the engine run any better, it's there just to increase the adjustment interval.

If you are experiencing rapid valve seat erosion, make a point of checking the remaining clearance before adjusting, and keep track of the numbers. You'll get a better idea of how frequently to adjust.

Of course, this raises another question of who to send your heads to. I had a disaster quite a few years ago after a valve job by a "BMW speed shop" in California. Exotic valve stuck and bent, then after repair the valve top came off and took out the whole left side. The shop was disinterested. Basically I was on my own. Expensive lesson learned: stick to BMW parts unless you know for sure the alternative is better.

The last "spare" heads I sent to Hansens BMW in Medford sat there for a couple of years, and I had to stop by and kick them into movement. A pair of heads I had done by a head shop in Seattle (used by the local BMW shop at the time) had a valve guide come loose. One pair I sent via a mechanic friend to his local auto head shop came back with different diameter seats in one head from the other. Worked OK, but I was a little suspicious. My son had a valve job done on his R100 at Bobs BMW in Maryland. I don't know whether they send the heads out, or do them in house. Very pricey, (and BTW they left a paper rag in the sump). I was unimpressed, although the valves seem to be working fine. Anyone have any experience with the "legendary Leo Goff at Memphis Motorwerks? Who does good machine work on BMW parts anymore?

pmdave :type

[barryg]

I am familier with Leo Goff at Memphis Motorwerks. I worked for Leo 12 years at both Memphis Motorwerks and Dobbs Motorsports. He is probably one of the the most competent engine builders worldwide, as he is internationlly known. Due a web search of him on the internet and see what comes up. Craig Vechorik of Bench Mark Works uses Leo quite often on the heads he restores for his customers. I can give you more references if needed.

[pmdave]

Thanks for the comments. I'll keep Leo in mind the next time I need some head work.

pmdave :thumb

[ggfossen]

PMDave

I'm a little surprised by your sour experience with Hansen's in Medford. Although I have not had major work done there, I have always found their attitude, and simple service, to be top notch. I also would like to mention that I had really good luck with Iron Horse in Tucson years back when Marty Cohen owed and operated the place. It recently sold, though, and I have no idea where it now stands in the scope of things, but I understand it sold in house, so I would image there is at least some continuance of like attitude.

I was in town yesterday, but found no Meguiar gold stuff at any of my stops. I will keep looking. My dash board did come in on time, but I probably won't get to the job until spring. Had to leave the truck precariously perched on the edge of the drive, and hike into the house with groceries. This morning was the tire chain thing with sweat and curses. Really a different weather pattern down here.

Gary

[pmdave]

Let me be clear that Craig is an excellent mechanic, and he has a long time interest in all BMW motorcycles.

It appears to me that his shop is just a victim of success. They have taken on several other brands, and struggle trying to keep everyone satisfied. Those small problems and obscure orders are easy to shuffle to the back burner.

pmdave :brow

[ggfossen]

PmDave,

Thanks for the vote of confidence for Craig Hansen. It does appear, by the way, that he is still very much in charge. Being local, as I am, I probably would not have a problem with repairs being set on the back shelf. I could easily be there often to know the progress.

Gary

[pmdave]

Let me be clear that I think highly of Hansens BMW in Medford Oregon, and of Craig Hansen, the owner and chief wrench. If I lived in the surrounding area, I would certainly frequent the shop.

My comments about the long-delayed heads is really a general observation of the industry. Small motorcycle shops can't really be expected to take on parts rebuilding for out-of-state owners. They don't get to charge for dissasembly/reassembly labor, since you took the machine apart, and they can't get reimbursement for warrantee if you didn't buy it there. So, it's really a favor, not a mainstream part of their daily business. That's especially true when the shop simply sends the component out to a local machine shop for the actual repair.

It doesn't make much difference where you ship an assembly for work, other than the cost of shipping. So, for the benefit of those of us who do our own maintenance, it would be great to know more about machinists or specialty shops who have a proven track record for quality work and reasonable turn-around times. (heads, transmissions, spline rebuilding, cylinder boring, alternator rebuilding, etc.) If you have good or bad experiences, please report in.

pmdave :type