Twincam harmonics = clutch spline wear?

[Darrell LeBlanc]

Hello, I have a question that was covered in an old archived thread, but it pertained to FF’s, which I think might be a different situation.

http://www.apexspeed.com/forums/showthread.php?t=10352

I have a Lotus Twincam/FT200 combination on my Winkelmann Formula B. I’ve been going through clutch plates (splines are shot) and input shafts at the rate of about every four or five weekends (the input shaft lasts a little longer). The adapter is in good shape and the alignment was checked (I think my mechanic said it was about 0.016 off, which is worse than what is mentioned in the archived thread, but he thought it was acceptable, so my # may be incorrect).

From everything I hear, the real problem is the lack of a harmonic balancer on my Twincam, which when run at over 8K RPM’s causes vibrations through the clutch and transmission. Is anyone else out there having similar problems with their Twincam? Is the only solution to pull the engine/transmission and replace the clutch plate every 4-5 race weekends and the input shaft about every 5-8 weekends? We are about to switch from a Tilton to an AP clutch plate, but I’m still interested if this is an known problem for all Twincams or something is wrong with my setup that I should continue trying to search for. Since the engine is out of the car right now, it’s a great time to look for alternate causes.

I think the old thread I referred to above is a different situation since the FF engines run at about 6.5K RPM, which puts different stresses on the clutch and input shaft. But if anyone can confirm that the same problem running a Twincam at 8+K RPM, that would be very helpful.

Darrell

[Chester Carter]

Had this problem with rt-1 with ft200 after experimenting with various solutions we ended up finding the ap discs last much longer. you can use them with the tilton pressure plate and discs if you want. never had to replace the input shaft again.
chet carter sf region. good luck

[scotts216]

I can't imagine that an FT 200 couldn't handle anything a twin cam could throw at it.....?

I run a twin cam with a MK 9 and get more wear than that.....

I assume that you have balanced the crank, rods,and pistons. And also you've balanced the flywheel and clutch together with the crank?

If not a balancing issue, then I'd still suspect an alignment issue. Something must be off???? The gearbox must be "cocked" and is not perfectly flush with the adapter somehow????

It's always something on these darn cars.......

Good luck.

[R. Pare]

.016 out of alignment is not good - especially with short input shafts. Every revolution the splines will shift against each other a tiny bit and wear each other out. The AP disk may have harder splines, but all that will do is decrease the wear on the dish splines at the expense of more wear on the input shaft splines. I would have your mechanic see what needs to be done to get the runout to less than .005.

There can be a variety of factors in old parts that can contribute to shaft misalignment : Has the front of the box been repaired? Has the bearing carrier been repaired? Is the input shaft bearing at the front of the box a C3 internal clearance class, or is it a higher class (less internal clearance)? Is the adapter ofut of alignment?

Any of those items can knock the shaft out of good alignment, and should be checked as part of the causality.

On possibility to look at as a potential cure - both for slight misalignment and for harmonics, is to use an AP clutch that has a center drive hub for the disks that is a separate piece (the disks spline to its OD).

That does not mean that harmonics are not a contributor to the problem.

[kea]

We have a Brabham BT-21 here in our shop, with a twin-cam. Years ago, we switched to AP clutch disks. If the input shaft gets bad enought to need replacement, then I put a new disk in at the same time. A worn hub on the disk, will beat up the input shaft sooner than it should, and it becomes an endless cycle.