TR4 & 4A, Flywheels and Clutches Oh My...

[TRDejaVu]

Hello all,

 

Long time TR guy. Had a TR4 and TR5 as daily drivers back in the old days; wish I still had the 5. Many years passed, as well as a couple of countries, and I now have a 62 TR4.

 

 

I am getting ready to pull the TR4 transmission to replace the clutch and convert to an OD trans. I am thinking about going the lightened flywheel route as well; nothing too extreme as I want it to retain street car driveability.

 

So, a couple of years back, I obtained a spares job-lot that included what looks like an unused flywheel (no surface marks and perfect starter ring), but it is from a 4A. There is also a diaphragm pressure plate in good condition with minimal wear.

 

I also obtained a "lightly used" TR4 pressure plate in excellent condition.

 

 

Finally, the questions:

 

Are the diaphragm clutch issues limited to the 6 cylinder engine application? Are they also due to the later gearbox? My OD box will be from a TR6.

 

Basically, do I stick with the robust and reliable TR4 setup, or is it safe to go with the 4A setup and make use of that flywheel?

[Bob Smith]

Remember that a TR4 clutch is 9" diameter and the diaphragm 4A is 8 1/2". You can safely use a 4A flywheel, driven plate & diaphragm cover as an assembly. You must change all three items not mix & match but you must change the release bearing to suit the diaphragm clutch. I assume that the starter ring gear on both flywheels has the same number of teeth on them so the starter motor will mesh OK. Whether you change or not is down to personal preference; some swear by the TR4 clutch others the later version. Can you find another 4A and try the clutch to help you make your choice?

[BlueTR3A-5EKT]

Bob is correct about the clutch to be used as an assembly to suit the flywheel - Remember you will also need to use the TR4A-TR6 clutch release bearing carrier.

 

And yes be sure to count the teeth on your ring gears. What does your starter look like? See the Moss cat for sketches and types.

 

The clutch of the TR4A does not use an adjustable push rod or return spring on the slave actuation - the TR2-4 does. If you go down the diaphragm (TR4A) clutch route I suggest discarding the return spring and if possible fit the fixed length item from a TR4A (or adjust your existing TR4 one to a suitable length, fit and leave alone) - the clutch will then be 'self adjusting' so long as the return spring is removed.

 

My own TR3 runs a Stag gearbox with TR6 input shaft and overdrive driven by a TR6 clutch assembly. There are no alignment or 'ratchet' clutch problems so often experienced by the 6 cyl owners. There are dowels in the rear face of your cylinder block that align the bell housing to the block - 6 cyl cars use dowel shanked bolts, that need to be fitted first when the gearbox is refitted to ensure alignment.

 

You can take a lot of weight off a TR4A flywheel and improve things no end. I think Kastner detailed this in his tuning book.

 

Cheers

Peter W

[TRDejaVu]

Thanks Guys and some great pointers.

 

I thought that the starter differences were only with the TR3 cars, as Moss states that starters are the same from TR3A TS50001 through the TR4A. Is that not the case?

 

Some people seem to have gone the Fidenza aluminum (or even aluminium) flywheel route. Not sure I have the $$$ for that, but still considering it. I don't have the Kastner book to refer to about lightening an existing flywheel.

[Alec Pringle]

http://www.kaskastner.com/kasbooks.html

 

Cheers,

 

Alec

[Bremer]

I'd like to see some specs for lightening a flywheel as well. Unfortunately Kastner's books don't detail how to lighten the flywheel. He says that all flywheels can be lightened by about 4 pounds, and that most of the weight is taken from the outside and the cylinder block side. Of course it's most beneficial to start off with an early (TR3) flywheel that weighs only 21 pounds instead of the later one which weighs 31 pounds.

[TR 2100]

I'd like to see some specs for lightening a flywheel as well. Unfortunately Kastner's books don't detail how to lighten the flywheel. He says that all flywheels can be lightened by about 4 pounds, and that most of the weight is taken from the outside and the cylinder block side. Of course it's most beneficial to start off with an early (TR3) flywheel that weighs only 21 pounds instead of the later one which weighs 31 pounds.

 

I'm not aware of any particular spec - it's more of a

personal thing - just how far you want to go.

I lightened my original TR4 flywheel (many years ago now)

using the earlier lighter flywheel as a guide as to what

was safe, i.e. how much to hollow out the middle.

 

I also took a little off the face and ended up with the

flywheel weighing about 18-19 lbs.

At the same time, I had the flywheel re-drilled to take

a TR6 diaphragm clutch as these are lighter, designed to

take more power and usually better balanced.

 

Be warned, though - there have been cases of flywheels

disintegrating, causing major damage to gearbox casing

and even ankles!

I tried to make mine as safe as I could be sanding and

polishing all the machined surfaces.

 

For TR 2100, I went the quicker and safer rouite and used

a new 'finger' flywheel.

 

AlanR

[stuart]

When I got my 4a (US solid axle variant) it had several large holes in the bell housing where something had exited sharply!

Stuart.

[Tr4Tony]

Hi

 

Also worth looking for a copy of JH Maclay's book on Triumph TR Maintenance and Modification (used copy on Amazon ?), plus Kas Kastner's original Competition Preparation manual (reprints on Amazon I think) - both set out pretty specifically where to lighten a standard flywheel and how much to take off. Having said that a competent machine shop guy will know pretty much where to cut. My experience is that about 18lbs is the lowest weight you can go to without making the resulting flywheel weak.

 

If you're not terribly bothered about using an original flywheel, the type TR2100 refers to is a good solution as you can use a later clutch, weighs about 9 lbs and are readily available. The primary disadvantage is that the revs drop of very quickly with a very light flywheel, so your gearchanges need to be quick and slick. If you can live with this then its probably a cheaper and better route to go down. Ive run one of these for 5 years now on a quick engine without any problems.

 

Regards

 

Tony

[TRDejaVu]

...For TR 2100, I went the quicker and safer rouite and used

a new 'finger' flywheel.

 

AlanR

 

OK, I'll bite. What's a "finger" flywheel?

[TR 2100]

OK, I'll bite. What's a "finger" flywheel?

 

Think of an 8-spoke wheel as against a disc wheel.

 

AlanR

[Smokey]

I guess I'll be in a minority here, but I don't quite see the point of lightening a flywheel unless the car is used for racing. A lightened flywheel will give you slightly quicker shifts on the track at high RPM, especially downshifts, but at the cost of more vibration and more difficulty in starting from rest. In addition, there is less mass for heat transfer from the clutch, so it's easier to burn out the clutch. I had a lightened flywheel and kevlar clutch disc on my Porsche Turbo track car, but standing street starts caused so much judder that eventually the release fork broke (at Mosport's Turn 5) due to fatigue. And lightening the flywheel has no affect on acceleration aside from the quicker shifts, since the inertia of the car is so much greater than the relative inertia of the flywheel. However, it's kind of neat to shut off an engine with a very light flywheel: it just stops instantly with a "whump". My Ferrari 250 GTE used to do that, but getting it moving from rest on a hill without burning out the clutch was another story.

[TRDejaVu]

Still thinking about the flywheel, but back to the clutch.

 

I know that there are different schools of thought on the diaphragm clutches; OEM vs. aftermarket. It is not my intent to open that up here.

 

Original pressure plate, not aftermarket.

 

- Does anyone know the wear specs for the pressure plate:

--- actual surface thickness?

--- allowable wear on the spring fingers where the release bearing contacts?

 

- Do they wear out? I know that everything wears out eventually, but for our hobby type use.

 

- What else goes wrong on them?

 

Thanks