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daywilmOffline
Post subject: Engagement Between Tranny and Clutch  PostPosted: Jan 15, 2016 - 11:05 PM
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What portion of the splined input shaft on the transaxle should the clutch hub engage? I think I've got a real problem. I'm mating a BMW v12 to a Porsche Boxster transaxle and I've had a custom flywheel made for it. Everything seems to be spaced properly except the input shaft of the tranny just barely engages the clutch hub (less than 1/4 inch by my estimate). If the hub on the clutch protruded more toward the tranny I think everything would be fine. Any ideas?
 
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RTOffline
Post subject: RE: Engagement Between Tranny and Clutch  PostPosted: Jan 16, 2016 - 05:44 AM
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Are you sure the hub on the clutch disc is facing the correct direction?
The hub might protrude more in one direction than the other and if it is in backwards it could produce the problem you have.
Remember, I don't know anything about your transaxle or the clutch you are using.
The clutch disc is usually marked which side faces the flywheel.
This is just something you could look at.

RT

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daywilmOffline
Post subject:   PostPosted: Jan 16, 2016 - 03:03 PM
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Thanks for the reply Ron. Yes, the clutch disk is in correctly. The sides are marked for "flywheel" and "transmission". After some research on the internet I believe I've found my problem. Apparently, the Boxster tranny uses a constant contact TO bearing. I measured the distance from the bearing face to the mounting face of the tranny with the TO bearing in it's static position. However, the slave cylinder is spring loaded and the TO bearing's normal position is with the plunger on the slave cylinder depressed some distance. I've yet to determine what that distance is but I suspect there is some wiggle room there. My question now is, "Do I have to trash my $600 flywheel or can I add a short pedestal to it to make up the difference?" My thought is that between the nine mounting bolts and three positioning dowels that I'd have machined into the pedestal maybe I'd be OK?
 
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RTOffline
Post subject:   PostPosted: Jan 16, 2016 - 10:09 PM
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It sounds like the basic problem you have is the transaxle input spline is too far back from the engine (the bell housing is too long or the transaxle is too short) or the flywheel is too thin. Either way, That places the clutch disc forward from where it is supposed to be for the spline on the trans input shaft to engage the clutch disc splines.
If I can assume the bell housing is a KEP or purchased bell housing for your application, that should rule out the bell housing.
If the bell housing is OK the front of the transaxle input shaft should go into the crankshaft centering bearing. This is worth checking.
If I can assume the transaxle is not modified, that should rule out the transaxle.
That leaves the flywheel.
Since you had the flywheel made, it is possible it is too thin and causes the issue you have.
So now what you are suggesting is some kind of spacer to make up the difference and move the flywheel back so the splines will engage.
That could be tricky. You will have all your horsepower and torque going through that spacer. It also sounds like that spacer will be about 3/4" to 1" thick (estimate only).
I have not heard of anybody doing that but it would have to be done correctly or you could have a dangerous condition. That is a lot of spinning inertia.
I would check again the position of the transaxle to the engine and make sure the problem is at the flywheel before I make any adapters or flywheels.
Again, I don't have a BMW V12 or Boxster transaxle. I am only imagining your situation and suggesting things to consider.
Good luck.

RT

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daywilmOffline
Post subject:   PostPosted: Jan 16, 2016 - 10:23 PM
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The Boxster transaxle is much like the Audi in that it has a built-in bell housing. The tranny has not been modified (that I'm aware of). Looking at Jim Dinner's custom flywheel he used on his V12 to Audi conversion, the distance from the base of the flywheel pedestal to the face where the clutch bolts on is much greater than what I have. Once again, I think this is due to not having the throw-out bearing in the correct position when I took my measurements. I understand your concerns about adding a spacer between the crank output flange and the flywheel. I have those same concerns but am no expert. It seems possible (maybe?) that if the spacer was machined properly and locating dowels were used to keep it in line along with the 9 mounting bolts it might be OK. But I don't know. Would it be possible to weld the pedestal (spacer) to the flywheel? I wonder about that as well. I just hate to throw over $600 down the drain if I can avoid it.
Thanks for your input.
 
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RTOffline
Post subject:   PostPosted: Jan 17, 2016 - 04:09 AM
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Oh, believe me daywilm, I understand the $600 issue!
I considered the welding solution but it has be done with care to not warp the flywheel.
Just be sure what you do is what you NEED to do before you do it.
These builds confront us with so many confusing dilemmas it is a wonder we survive.
You are so much closer to this problem than I am, all I can do is imagine what you are faced with.
Just go through this logically and you will get it right.
Remember the old adage: measure twice, cut once.
You will make it through this and will enjoy the challenge.
Re-check the position of the transaxle input shaft to the engine crankshaft. That will be the final key to the problem. If it is positioned correctly, you will have to address the spline engagement with another solution, such as the flywheel thickness or whatever else it might take. You do need to have the front of the input shaft go into the bearing in the rear of the crankshaft.
Just as an aside, if the input shaft is inside the crankshaft bearing, I can't understand why the clutch disc spline would not be on the transaxle input shaft. The throwout bearing should ride on the extended housing behind the input shaft spline (if it is anything like the throwout bearings I know).
So keep at it. Sometimes you just need tho sleep on it and you will wake up with the simple answer.

RT

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sisqocrackerOffline
Post subject:   PostPosted: Jan 18, 2016 - 03:06 PM
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My 2 cents on it. I wouldn't worry about the spacer idea. I've got one in my V8 build. There a lot of them on the road from V8 Archie builds. If it is dynamically balanced, I wouldn't worry about it. Marking it so it is clocked properly is a must of course.

In my setup, my flywheel is zero balanced (as my motor is internally balanced at zero itself) so if you have your flywheel set, then I would make (or have someone make) an arbor for it. Then have a shop that makes your spacer check your flywheel on the arbor, with and without the spacer to make sure the whole assembly is balanced the same in both respects.


Thanks,
Coop

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