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Old 10-02-2011, 04:44 PM   #16
supershaft
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Quote:
Originally Posted by wmax351 View Post
That's a good point. It does seem as if the marks are exactly where the valve would be if it were at least mostly closed. Otherwise, the marks would be closer to the center of the piston.
Yes, the valve is mostly closed but it isn't closed. The piston isn't around either valve when they are mostly open. The exhaust is closing as the piston comes up.

Since both your valves are hitting and it seems to be running alright otherwise, it has to be the base gasket? You did adjust your valves correctly with the proper lash?
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Old 10-02-2011, 04:48 PM   #17
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Quote:
Originally Posted by supershaft View Post
Yes, the valve is mostly closed but it isn't closed. The piston isn't around either valve when they are mostly open. The exhaust is closing as the piston comes up.

Since both your valves are hitting and it seems to be running alright otherwise, it has to be the base gasket? You did adjust your valves correctly with the proper lash?
Valves adjusted to proper lash, on the loose end for break-in, checked at both hot and cold.


Quote:
Originally Posted by Airhead Wrangler View Post
Any chance you're a couple of teeth off on your timing chain??
I'm wondering about that. I farmed out the bottom end to a guru, and he took care of the timing chain. Seems an unlikely option.
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Old 10-02-2011, 04:52 PM   #18
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They either won't run or barely run thusly. I have seen people do it and nothing touched in the cases I have seen. Twice I think? Maybe they were timed early both cases?

Plus, if it were that I would think only one valve would be getting into the piston? Favoring the exhaust valve would be late timing and I don't see that getting the intake into the piston at all.

supershaft screwed with this post 10-02-2011 at 05:00 PM
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Old 10-02-2011, 04:58 PM   #19
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^ good thinking! I'd check that out. If the timing is right, I'd try the thicker base gasket, but you should check the clearance with modelling clay or rosin core solder to see that this does in fact give you the needed clearance.
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Old 10-02-2011, 05:43 PM   #20
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Originally Posted by supershaft View Post
They either won't run or barely run thusly. I have seen people do it and nothing touched in the cases I have seen. Twice I think? Maybe they were timed early both cases?

Plus, if it were that I would think only one valve would be getting into the piston? Favoring the exhaust valve would be late timing and I don't see that getting the intake into the piston at all.
It ran perfectly, so that may be lower on the likelihood scale.
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Old 10-02-2011, 07:08 PM   #21
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Originally Posted by Airhead Wrangler View Post
Any chance you're a couple of teeth off on your timing chain??
That's what I'm thinking-- that would be the only way that the piston and the valve could be in the wrong place at the wrong time. Time for an extensive teardown-- that's the trouble with a Beemer-in-a-Box, even worked on by gurus.

The "normal" base gasket wouldn't do that, it's what is supposed to be on there, stock. ANd from the piston marks on the exhaust valve, the valve isn't rotating as it should.
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Old 10-02-2011, 07:12 PM   #22
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No expert advice but...

When it comes to timing(I know, beating the dead horse), I myself got a wonderful death rattle out of my motor after tearing one side apart after wrecking my R60/6. I had set the valves on waste not ignition, I addressed that and noise was still there to drive me insane.
I tore into the motor(again) only to find that both lifters were sticking in their bores. Some debris from the wreck(the valve cover and dirt from the median) had gotten into the motor and the lifters were moving, but it took huge effort to move them. I had some very slight damage to my piston, not as bad as yours but still it was there. A good cleaning fixed the problem right up, and she now hums like a sewing machine.
As a professional auto mechanic I rarely run into stuck lifters but it does happen and can cause that exact same damage. If the lifters are stuck the piston will "knock" them shut with little physical damage to the valves. If it was sitting in pieces as long as you say it might be a point of concern. I'm in no means as well versed with the airheads as everyone else but it can happen, its happened to me. Just throwing some fresh ideas around
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Old 10-02-2011, 07:26 PM   #23
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I could see that happening with an airhead. I never have but I could see it.
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Old 10-03-2011, 04:51 AM   #24
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If the parts are unmodified, I'd first suspect bad cam timing. The R75 doesn't need the thick spacers to keep the valves away from the pistons.

The reason I asked about the exhaust valves is that the valve edge is scraping the edge of the pocket. I ran into a similar problem with an R11S motor that had 'mod clash' with different valves and pistons. However, that aside you can see that the valve is still bottoming out on the piston. The valve head is probably flexing to the outside when the piston hits it, causing it to dig into the pocket edge. You'll definitely need to check the valves.

The thing that puzzles me a bit is that if this is because the cam timing is wrong, I would expect to not see both the intake and exhaust hitting. One or the other, but not both. Maybe I'm just not visualizing it right.

Might as well measure everything. Cylinder height, valve spring height, conrods, head thickness, and of course inspect the cam timing (pulling the timing cover is easy, in case you haven't done it before). Post your results and we'll take it from there.

Don't assume that the problem isn't in a certain place because a pro did it. If pros did every part of this job, and something's wrong, then someone missed something, even if it's just an incompatibility between modifications like the R11S I mentioned.
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Old 10-03-2011, 04:56 AM   #25
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Another thing: how long did it take for this to happen? You mentioned that you have 100 miles on it, but if it was like this at start-up I doubt you'd have ridden that much. I can't see a blown conrod bearing giving enough slop to cause this, but maybe the valve springs are weak and the valves float at lower RPM than normal. Did it start suddenly and then not go away, or did it happen only at a certain RPM, or what?
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Old 10-03-2011, 09:29 AM   #26
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Originally Posted by AntonLargiader View Post
Another thing: how long did it take for this to happen? You mentioned that you have 100 miles on it, but if it was like this at start-up I doubt you'd have ridden that much. I can't see a blown conrod bearing giving enough slop to cause this, but maybe the valve springs are weak and the valves float at lower RPM than normal. Did it start suddenly and then not go away, or did it happen only at a certain RPM, or what?
It pretty much started immediately. It got louder as time went by though. Initially, I figured its just the valves making noise, but then it progressively got louder.

I'll have my dad pull the timing cover this week, and check the valve timing.
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Old 10-03-2011, 10:29 AM   #27
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Hi Wmax351

I know all the parties involved ..let me know if I can help..pm me.
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Old 10-03-2011, 10:52 AM   #28
supershaft
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Originally Posted by wmax351 View Post
It pretty much started immediately. It got louder as time went by though. Initially, I figured its just the valves making noise, but then it progressively got louder.

I'll have my dad pull the timing cover this week, and check the valve timing.
I was thinking rod bearing and valve spring too but it is east to push/pull on the rod and look at the springs to see if one is broke.
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Old 10-03-2011, 12:14 PM   #29
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Quote:
Originally Posted by AntonLargiader View Post
Another thing: how long did it take for this to happen? You mentioned that you have 100 miles on it, but if it was like this at start-up I doubt you'd have ridden that much. I can't see a blown conrod bearing giving enough slop to cause this, but maybe the valve springs are weak and the valves float at lower RPM than normal. Did it start suddenly and then not go away, or did it happen only at a certain RPM, or what?

Valve float is pretty obvious. The engine acts like you've hit a rev limiter.

(Years ago, I used valve float on a Triumph 500 Trophy to tell me when to shift up, it was obviously a lot more forgiving an engine than an R100 engine is)
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Old 10-03-2011, 12:22 PM   #30
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Have you had the flywheel off. Just wonderin if it's been alighned back proper?
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