Kent engine clutch questions

[george schilling]

I'm putting my car back together after a rear thrust bearing failure on a fresh engine. I'm a novice in FF. Not wanting to make the same mistake twice, I'm wondering if 5.5" Tilton clutch could have contributed to the failure. The question was raised by Scotty at Taylor Engineering, the thinking being that the initial force to engage the clutch may be excessive. My engine guy says no. What say the experienced guys out there. What are your experiences with the 5.5" clutch compared to the 7.25 and stock clutches? I'm using a Saab slave cylinder. Also, what have you found to be the preferred pilot bearing? The car will be used for autox including Pro Solo's.

Thanks for your help guys.

[John LaRue]

That was the set up that we used for many years. We did experience some issues cracking friction discs; that was resolved with some modifications to the disc.

[Purple Frog]

There was a thread on thrust bearing failures on the Kent and their causes about a month ago. Might be worth a read. e.g. sometimes the input shaft can be too long.

[kea]

When I started F/Ford racing in the 70's, even before the current style racing clutch was legal, I was told not to hold the clutch pedal down for long periods of time. The worry was excessive thrust bearing wear.
If you current clutch takes more pressure to work that you think it should, maybe the guys at Taylor are on to something.
I am not a big fan of the 5.5" clutch, for one reason, because of the effort it seems to take to dis-engage.

[Brian]

I have heard that the new blocks have main caps machined for two thrust washers instead of one. That would be a good upgrade.

Brian

[Jim Garry]

Since you plan to autocross the car, there's another consideration. The stock clutch is much easier to use given autocross requirements such as (1) lots of driving around in the paddock and in grid, (2) ease of use for standing starts, although some will say the smaller clutch makes that more efficient, it is also more difficult. Consistency and ease are critical in Solo where we only get a few shots.

I used the stock clutch in my FF for 14 years and never had a problem. First (already used) clutch lasted 9 years. Second clutch is still in the car. Ease of use was excellent. My earlier FF had the 3.5 and it was a b---h to use for my purposes.

Just my $.02.

[Dick R.]

George,

How stiff are the pressure plate springs for a 5.5?

Jim's points are good and for all I know may be one of the reasons for the success Jim and the previous owners had with the car.

Jim, did you lighten the flywheel when the rule changed?

George,

But if you don't want to run the heavy stock system there is the 7.25 which I've run for years with no problem. The pressure plate springs are one step up from the "normal" FF1600 springs for the 7.25. If "normal" is "buff" mine are "orange". No thrust bearing or other issues. I used to do LOTS of Pro Solo starts and still do lots of driving around the paddock/grid as needed but winch on/off the trailer. I even shift using the clutch. The key for me is don't slip the clutch so it doesn't build heat. For high traction hot tire launches I just add revs so the tires slip instead of the clutch.

Dick

[-pru-]

George,

But if you don't want to run the heavy stock system there is the 7.25 which I've run for years with no problem. The pressure plate springs are one step up from the "normal" FF1600 springs for the 7.25. If "normal" is "buff" mine are "orange". No thrust bearing or other issues. I used to do LOTS of Pro Solo starts and still do lots of driving around the paddock/grid as needed but winch on/off the trailer. I even shift using the clutch. The key for me is don't slip the clutch so it doesn't build heat. For high traction hot tire launches I just add revs so the tires slip instead of the clutch.

Dick

I echo Dick's comments regarding the 7.25" clutch. Great service life and, once you are use to it, easy enough to modulate when driving around the paddock. For starts, just keep the revs up and dump it; wheel spin reduces the shock to the drivetrain.

Take care,

[Jerry B.]

'"""" a rear thrust bearing failure on a fresh engine.""""

Usually the cause is no or low oil pressure when pushing the clutch in and the motor running. Do not start the engine with the clutch pushed in. Especially with a cold motor or before the oil pressure comes up.

The more pressure plate pressure, the more the thrust bearing is aggravated.

""""I'm using a Saab slave cylinder. """"

Make sure you have adaquate t/o bearing to finger clearance. You do not want contact of t/o bearing to fingers with the pedal out.

"""Also, what have you found to be the preferred pilot bearing?""""

Either an oilite solid bushing or the needle bearing type. Index the adapter plate so all is square with the world. But that would not contribute to a hammered thrust bearing.

Good luck.

[Dick R.]

'"""" a rear thrust bearing failure on a fresh engine.""""

Usually the cause is no or low oil pressure when pushing the clutch in and the motor running. Do not start the engine with the clutch pushed in. Especially with a cold motor or before the oil pressure comes up.

Good luck.

So that's why Skip Barber instructors told me to have the transmission in neutral (of course ) and the clutch out when starting the engine. I knew it was something about load on the thrust bearing but that was in 1991 so it has been "awhile".

Dick

[Bob Clark]

When I started F/Ford racing in the 70's, even before the current style racing clutch was legal, I was told not to hold the clutch pedal down for long periods of time. The worry was excessive thrust bearing wear.
If you current clutch takes more pressure to work that you think it should, maybe the guys at Taylor are on to something.
I am not a big fan of the 5.5" clutch, for one reason, because of the effort it seems to take to dis-engage.

I agree with Keith... You may even want to look at a stock clutch if it is just an autocross car. The other thing you need is a pedal stop on the clutch pedal. The pressures when the pedal/clutch plate go over center are very high and can be a cause of thrust bearing issues...
There was a vender at PRI last year that had a display with gauges and when the pedal went over center it was in the 900lbs range!!! Yikes!!

[george schilling]

Reading these combined with speaking to Scotty and my engine builder have cleared up several questions that were troubling me. The failure happened on our first day out. We were using the clutch quite a bit in the paddock and grid when oil pressure was low. This may have prevented oil getting to the thrust bearing. From now on, there will be a lot less clutch depressing and a lot more neutral and pushing the car in grid as long as we have the 5.5" clutch. I think I'll stick with the 5.5" until failure then decide whether to go with a larger one at that time.

Bob - Thanks for the tip about the pedal stop. I'll make a point to be sure that's adjusted

Dick - Neutral it will be

Jerry - Very informative post

Pru - good advice

Back to Dick - The 5.5 provides 250 lbs of clamping force, but Scotty tells me the initial force required to depress the springs of a 5.5 approaches 800 lbs. Our first time out we still had the road race gears in making it a challenge to get the car rolling. With the installation of the new low first gear, getting the car going in grid will be easier, but you can bet we'll be doing a lot less slipping and more dumping the clutch.

Jim - What throw out system are you using for your stock clutch? Will a Saab slave give enough throw to depress the long fingers on the stock clutch?

Brian - Wish I had thought of that when the engine was torn down. Would have been a nice upgrade.

Kea, Purple and John - Thank you for your input

[Jim Garry]

Jim - What throw out system are you using for your stock clutch? Will a Saab slave give enough throw to depress the long fingers on the stock clutch?

Saab.

[Brian]

I am not sure but I don't think a Saab throw out bearing is the right diameter for a 5.5" clutch. I use them on 7.25" clutches and I think the bearing diameter is different between the two, with the 5.5" being smaller and having greater leverage against the clutch fingers. That would contribute to a higher than required pressure.

brian

[george schilling]

I've gone over the set-up with Scotty @ Taylor. He's given it his blessings as being correct. Thank you for the thought.

[george schilling]

I am not sure but I don't think a Saab throw out bearing is the right diameter for a 5.5" clutch. I use them on 7.25" clutches and I think the bearing diameter is different between the two, with the 5.5" being smaller and having greater leverage against the clutch fingers. That would contribute to a higher than required pressure.

brian

Turns out the mounting spacer the fits between the annular slave and the bell housing was too long. A shortened one is on the way.

[george schilling]

Update on this thread. Scotty machined a new block plate .300 shorter than the last giving me .150 clearance to the clutch fingers. I've got about 50 runs on the car and no issues with the oil pressure or thrust bearing. The 5.5 " clutch was a challenge getting used to, but Joey and I can finally get around in the car without stalling it. I do have a problem with the car cutting that I'll describe in a new thread.

I went back and read through this thread. There was a lot of good advice and observations contained here and I really appreciate everyone taking the time to weigh-in.

George