Matt P's Flywheel Issue

In the November ON, Matt talks about a strange alignment (or lack thereof...) of the timing mark on a '92 R100GS.
QUESTION: It's been a long time since I've been inside an airhead, so - Is it possible that the factory (or somebody) installed that flywheel "backwards", that is, with the wrong "face" forward? (And then it would be impossible to align its timing marks to TDC.)



And as long as I'm displaying my ignorance... Wes's sketch on page 40 does Not show a "flathead" screw top: that's a "Straight Slot" head. The only way to see that a screw is a flathead would be by rotating the view 90 degrees in any direction.

Would there be the mounting locations for the clutch on the reverse side of the flywheel? Seems unlikely.

That's an interesting problem he's got. And several Airhead experts have been consulted as well. That's the first time I've seen Matt get stumped by something.

I've only seen this happen one other time with a BMW; and that was on a K75S that had a mysterious vibration.

I think the housing cover screws into the pressure plate - not the flywheel.

Can't be the flywheel. The bike was running after being tipped over and hydro-locked. It stopped on the way to Matt's house and had to be pushed the rest of the way.

I don't know crap about BMW crankshafts, but I never had seen an engine where you could flip the crank end to end and make it work. Mounting for the flywheel, drive sprocket or gear for the cam drive is always specific.

Yes it was running before the tip-over... but this timing issue was discovered in the course of troubleshooting. It's probably not a "Root Cause", but it certainly demands investigation (which could in turn lead to the cause of the no-start) and correction as long as things are apart.

Of course the crank cannot be flipped end-for-end; but the flywheel mounting does indeed have FIVE possible solutions, 72 degrees apart each ... and that's before considering if it can be flipped wrong face forward, which, if it can be, makes for ten possible positions. Note that some airheads have been found to have had their wheels incorrectly installed by the factory's assembly line.

I wonder if anything "different" might then show up on the starting ring's teeth...? Maybe not, if the wheel is symmetrical front-to-back, or its position on the shaft was otherwise altered.

"Many of us are more capable than some of us, but none of us is as capable as all of us." - Tom Wilson

Ahh, I get your drift. I got hung up on Harley lingo where the flywheels are the crankshaft.

Are the holes equally spaced? Typically when a part like this needs to mount in one position there is a locating pin, or one hole is moved slightly so the part fits in only one position. I would think German engineering would do something to ensure it gets mounted properly.

PoorUB said:

Ahh, I get your drift. I got hung up on Harley lingo where the flywheels are the crankshaft.

Are the holes equally spaced? Typically when a part like this needs to mount in one position there is a locating pin, or one hole is moved slightly so the part fits in only one position. I would think German engineering would do something to ensure it gets mounted properly.

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Nope. It can be mounted in any of 5 positions.

PGlaves said:

Nope. It can be mounted in any of 5 positions.

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But only one of those 5 possible positions will show the OT mark in the timing window when piston is at TDC. Both have to happen to be correct. If flywheel is mounted incorrectly, you can paint your own little "f**ked up" dab on the flywheel.

Friedle

Friedle said:

But only one of those 5 possible positions will show the OT mark in the timing window when piston is at TDC. Both have to happen to be correct. If flywheel is mounted incorrectly, you can paint your own little "f**ked up" dab on the flywheel.

Friedle

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Of course. I was attempting to answer the question as to whether it would only mount one way.

PGlaves said:

Of course. I was attempting to answer the question as to whether it would only mount one way.

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We are saying the same thing Paul....in two different languages. Midwestern and Northeastern.

Friedle

Matts problem

Friedle said:

We are saying the same thing Paul....in two different languages. Midwestern and Northeastern.

Friedle

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My question: if you set the pistons at TDC and mount the flywheel with the timing mark near the inspection hole in the flywheel cover, how do you get to be out 120 degrees?
It seems to me you can only be out either 15 degrees or so (i.e. the advance) or you're out 360 degrees because your on the wrong stroke (compression vs. exhaust)? But isn't that a camshaft to crankshaft timing issue?

It is baffling but I'm with Friedle on this one.

mats problem

Hello, I was thinking, the bike ran ok until the crash I believe, then ran almost back to Matts home, then refused to start ,perhaps the exaust has gotten blocked with dirt or bashed enough to block the exaust, this will stop fresh air etc entering the combustion chamber stopping the engine from starting, we did this in Ireland when we were kids stuffing a potato up the muffler of a car it would stop after a few minutes, just a thought looking forward to his return to see what he finds, bye for now Jimmy

Timing mark alignment

In the case of the mis aligned timing mark, everyone has to remember, there are people who work on their engines who should not be working on their engines.

If someone cannot figure out if the engine is at top dead center, or does not take the time to determine if it is, they have no business working on an engine.

Case in point, my friend's R80RT, the flywheel was installed incorrectly, just as you are talking about. This was done during an oil leak fix. The previous owner changed the oil pump gasket, but did not change the leaking rear main seal. When he put the fly wheel back on, he had it out of alignment and the timing marks did not line up.

When my friend an I changed the leaking main seal, we put thing to right.

The people I feel sorry for are the new owners of bikes worked on by careless, incompetent, dishonest people, who find themselves trying to figure out what the heck is going on with their new to them bike. A bike that should be giving them joy not heartbreak.

Repair guides are not expensive and they are available. Yes, sometimes you need to have two of them because they might just once in awhile conflict with each other or, one may show a slightly different way of doing things but everyone should have one for the year make and model of the bikes they are working on. Even if it is just to do an oil change.

There are a fair number of people who can in fact do repairs without guides, due to experience or talent, the fact is, most of us do not have this trait. Contrary to belief, it is a good thing for a man to read the directions from time to time. St.

It reminds me of a guy I used to work for. We did HVAC work, but also sold standby generators. We had a customer call in because his generator would not run. I went out and looked at it and discovered it had broken both connecting rods. It just clattered when I spun it over. I verified it by pulling the spark plugs and it had zero compression, and I even stuck a ink pen down against the pistons and spun it over, and the pistons didn't move. (A V-twin Briggs and Stratton) I went back and my boss asked me what was wrong and I spent the next 15 minutes trying to explain how I knew the connecting rods were broken without tearing the engine apart. He wanted me to go back and pull the engine and tear it down to make sure, probable a 3-4 hour job. He just didn't get it. I finally told him I would bet my next years paycheck and he decided to take my word for it.

Another time I looked at one that the valve timing was off. Valve overlap was occurring with the piston about 1/2 way up the stroke. Another 15 minutes wasted trying to explain how I knew the timing gear key had sheared without taking the engine apart.

PGlaves said:

Nope. It can be mounted in any of 5 positions.

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IMO, that is really screwed up! If the part needs to be mounted in one position, but can easily be mounted other wise it should be keyed or located with odd bolt placement to ensure it gets mounted as it should. Unbelievable that German engineering would ignore this!

Yes, but in this case the bike was being ridden in the mountains! The problem only occurred after it hydro-locked after being left on its side after a tip over.

I don't understand where this flywheel discussion came from. Something changed after the tip over/hydro-lock. Or am I missing something?

Matt thoroughly documented his attempts to figure out what was wrong. As far as I can see from what he wrote, he found nothing mechanically wrong with the engine...he eventually got to the point of removing the crankshaft and camshaft. All in all, he found nothing wrong.

His test of running the engine with the transmission removed showed that the ignition was firing at TDC at the very bottom of the rotation, or at 120 degrees advanced as he wrote. If there are 72 degrees between any of the 5 bolt positions, then the flywheel likely isn't mounted wrongly. 120 degrees advanced doesn't agree with any combination of 72 degrees.

I suspect something is wrong with the electrical side, although he changed the Hall sender and looked at another similar setup and found nothing amiss. What would cause the firing point to move like that, I can't imagine.

My original question remains unanswered...

Where it came from is the fact that Matt discovered it in his experienced and straight-forward methodology of troubleshooting. As I said earlier, it's not a Root Cause, but there's NO reason to not attempt to discover Why and correct it as long as everything is already open anyway.

I've spent about ten minutes looking at pictures of airhead flywheels as shown on Google - and I found nothing that indicated they couldn't be mounted "wrong face forward". Ditto the parts fiches for various years on MAX's site (although of course there are differences in flywheels over the years).
Didn't spot anything about it on Snobum's pages.
Likely the authors of shop manuals presume that the mechanic already knows that "this mark has to happen here" and therefore don't bother to caution the reader.

Question for any geometry wizards: If the pattern is flipped over, how many degrees would the timing mark move?
Just as a WAG, let's "assume" it would move by 144 degrees, two bolt holes' worth.
Then the flywheel could be moved two holes; follow that up with a combination of points plate position plus the points' gap, and a few more degrees could be had (either at TDC or full advance).
Would this get the alignment back...?

btw - re my note about the flywheel's starter teeth: Some years had spacers on the 5 bolts that moved the assembly on the shaft; whether or not they are required - or there at all - would affect what happens on the teeth's mating surfaces. But this is secondary to the actual issue.