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Triumph TR6 - Flywheel Lightening Advice Needed

Hi.In December Don Kelly noted that he had his flywheel lightened "about 7 pounds" for around $100 US --
Don --Is the 7 pound loss a nice change ?
What are your reactions ? Thanks for your inputs. Dave Johnston, Seattle,Wa
David Johnston

My flywheel is lightened by 13#s ,about 1/2 original weight, bought from PRI. Many benefits touted but cannot verify yet as still not up and running, but orig is very heavy.
Peter G

Be careful- if a flywheel explodes it can burst out of the clutch housing and smash up your feet/ankles. Best to use one lightened by/for TR6 racers.
P H Cobbold

Even then, don't the racers put in heavy steel plate between the aluminium bell housing and the tunnel cover to prevent the shattered flywheel from coming through the tunnel and shattering their feet and ankles ?

Don Elliott
Don Elliott


My two penneth(cents).

That plastic, come fibreglass transmission tunnel on my old banger does worry me.

Its not quite the same as having a mono body and chassis with a lot of in-built protection, if you can call it that.

I want to go for lighted flywheel too, but it is always in the back of my mind regarding a nasty happening.

Just out of interest Don, I guess the suppliers of "tuned" flywheels in the Staes and Canada have/use some sort of disclaimer regarding flywheel explosions ....

Any comments ?

Best Regards (73,s)

Bob (G7HJG)
Bob Blewitt

I'll try to find out and let you know.

BTW were you at the TR Register International in 1991 at the Staffordshire Fair Grounds. I was there.

Don Elliott, Original Owner - 1958 TR3A
TR Register member since 1987
Don Elliott

Bob - on the exploding flywheel - I purchased a Fidanza aluminum wheel and spoke with a Fidanza employee about the safety issue. For what it's worth, the thought process around that seems to be there is no issue at stock TR6 engine speeds. Apparently a very high rpm is required to explode a flywheel.

I have since learned, however, that there are problems with improperly mounted aluminum flywheels. The aluminum wheel is an interference fit and is not easy to get on the crankshaft. It needs to be heated, then installed, then removed and the friction marks checked to see the wheel seated all the way down, then heated again and installed on the crankshaft for the final time.

73 TR6

John Parfitt

David- as to your original question,does it make a difference. Since I installed it with other mods I have not had the chance to finish it. I'm in the process of building a larger shop for it. If you live near Seattle,call Autosport and ask for Brad.

The PRI wheel is not aluminum, but a beautifully and intelligently machined piece of work, not weakened in any way. I have complete faith in it. Peter G
Peter G

A personal view.

It's a question of balance - is this a full race car or a daily driver?
If all you did is lighten the flywheel it would be a waste. If you were doing it in conjunction with serious upgrading / balancing of engine components it would make an incremental difference. The question is, how does it affect overall perfomance vs driveability? A lighter flywheel will give the engine marginally faster pick up and slightly quicker run down from high revs at the expense of low end 'torque'. The low end 'torque' makes it more relaxing to drive in traffic (stop/start) and carries you further with your foot off the gas pedal. The lighter wheel should make gear changes easier on the track (5000?rpm).
Don't forget that the assembly includes the weight of the clutch when in the car. Alu flywheel should be mated with an appropriate (lightweight)clutch.
You should only remove material from between the ring gear and the clutch plate. The further out from the centre the more effect it will have. Ring gear is expanded with heat and 'shrunk' onto the flywheel by cooling.- Could heat build-up in the thinner flywheel be an issue for the ring-gear?
I have a 170+ bhp PI car which I use every week on the roads and a couple of times a year on the track. The steel flywheel was lightened by about 6 pounds and the assembly balanced with the (laycock) clutch plate attached. It drives nicely around town and my wife and son don't stress when they drive it.

Roger H

Don E,
Yes I believe racers do weld in a thick steel plate. There is usually a minimum weight limit and that plate is low down so helps lower c of g too. Not sure if they bother with the passenger's side! Small diameter multi-plate clutches seem to be favoured, and of course everything is balanced, and 6500rpm normal.
I met a vintage racer who had a lightened flywheel in a single seater special with a big old V8 lump. His feet survived a flywheel explosion purely because he had moved the seat and pedals rearwards a few weeks previously. The flywheel destroyed the bell housing and bits still had enough energy to pass through the firewall and then the bonnet.
P H Cobbold


I checked with Ted Schumacher. He will only sell new flywheels. Never an original flywheel which has been lightened for that very reason.

Ted writes, "We have a manufacturer who makes new aluminum or steel flywheels for us. Aluminum is 12.4 pounds. Picture is on our web site. Thanks, Ted."

Ted's web-site is:-

Ted Schumacher
108 S. Jefferson St.
Pandora, Ohio, USA
Fax: 419.384.3272 (24 Hrs.)
Phone: 800.543.6648 (US & Canada)

Submitted by:
Don Elliott
Don Elliott


Thanks for the email cc.
Didn't join the Register until recently, only been to Malvern last year. But we are going again this year without doubt.

I must admit I had no idea an aluminium flywheel was so difficult to fit.

Teds website

is a very useful site indeed, the picture of the ally flywheel is great.

Not quite sure where this leaves things. As the PI TR is so torquey even my '73 I wander how the pulling power low down the band would change.

Best Regs all.

Bob Blewitt

Thanks everyone for your views/comments.
Don Kelly--thanks for the lead - I spoke to Brad at Autosport this afternoon and I'll take the flywheel to him for the work.
For everybody elses info: They will lighten (approx 7 pounds), surface , then balance the flywheel with the pressure plate attached -- $120-150 total.
Now, if someone who has actually driven a TR6 with a lightened flwheel will contribute some observations I'll feel more comfortable making the committment !

David Johnston


I think the reason you are getting little definitive feedback to your question is that the reality is that the difference is small - (not to say that it isn't there!)It is very subjective and in my experience, subtle changes in the 'driveability' of the car can occur throughout any given day!!
Topping up the tank on a cool morning will give you a different 'feel' to a 1/4 full tank on a warm evening . Replacing worn tyres with identical new ones can change acceleration markedly.
My advice is that if you have roller rockers, hepolite pistons, forged rods, etc etc - go for it with an ally setup - otherwise, there are better things to spend your money on. If you have a nicely put together 'fast road' setup, knock a few pounds off your existing wheel - it all helps - even if it's only reducing the overall weight of the car.
I visited Racetorations in UK when I was in the middle of re-building my six and had a long chat with Darryl Uprichard. I left several thousand dollars lighter but without the ally flywheel, racing clutch or limited slip diff. I left comfortable with the knowledge that you have to spend a LOT more money for the smallest of gains when you're trying to get the ultimate out of the car.
Roger H

Roger's comments support my conviction that, for a road car, the conventional tuning approach may not be the best or most cost effective. My conversations with a succesful TR6 racer ("around 10k to build a competitive racing engine") convinced me that supecharging would be a fraction of the price. Racing engines are invariably poor on low-down torque, run rough below 1000rpm and wear out rather rapidly as that exotic power output is only achieved at rpm that are excssive for a long stroke engine. In complete contrast a supercharged engine is beautifully smooth on tickover, and most importantly has 30-50% more torque across the rev range. Torque makes for acceleration. So why do we not see the TR6 specialists selling blower kits to bolt onto the engine (no internal mods are necessary, not even a cam change)? I surmise that most of the specialists have developed thir reputations through racing, and supercharging carries a 40% cubic capacity penalty in determining a car's racing class. So they never build up expertise with blowers. But the fact that a race car has to be penalised so severely for being supercharged tells us how effective a blown motor can be!
P H Cobbold

Interesting aqbout Ted and the flywheel. He recomended to me when he did my heads that you should not use a lighter flywheel just for safty sake. Now he's selling one.
Don K.

Well, it's a flywheel designed from the start to be lighter rather than a cutting down a heavy steel flywheel designed to be safe. Kas only recommended taking 4 lbs off the stock flywheel, I believe.

Peter, you ARE an advocate to a blown TR6! I'd sure like to drive one!

Brent B

Well, this has turned into quite an interesting discussion. I spoke on the telephone this afternoon with Ted Schumacher about flywheels --He still adamantly refuses to sell a lightened stock flywheel through his shop , however, the reason appears to be one focused on product liability issues --the bane of American business. He has no way of knowing if that used flywheel has been dropped once or twice in its 30 years of life or might have not been made to the exacting standards that Triumph specified. His aluminum flywheel is very nice , but at 12.4 pounds seems like too far to venture with my street car- he'll also make a light steel flywheel but that will cost over $400.
I have just received from other listers e-mails reporting that they've taken approximately ten pounds off a late model flywheel with no ill effects at all --idle on up. Starts are smooth and jerk free --now this is with an 18-19 pound flywheel. Another lister with a '69 reported that his flywheel was lightened by 3 pounds from the original 21(!) pounds and he likes the results also --I had no idea that the flywheel weights were so different. I'm beginning to wonder which flywheel Kastner was recommending to have 4 pounds removed from ? Apparently the early cranks have an integral "extension"(missing from later cranks) that the flywheel bolts to, maybe the total weight on the end of the crank is about the same either way ? (It's time to get out the parts books to take a good look at the different years )
And to add a bit of zest here too, I'm planning on having a supercharger on my car by springtime. I too, feel it might be a perfect way to liven up performance on this wonderful car. There's lots of fabrication yet to be done and even the blower itself may be hard to find, I'll report. If anyone would like to see the e-mails I received from the satisfied light flywheel users send me a message - I'll cut and paste them to you.
All the Best !
David Johnston

Just to confirm what Mr.Cobbold said above - it may have been the same car. At Mallory Park a couple of years ago, US car with a V8 - forgotten the marque - exploded its flywheel on the start/finish straight. Half the clutch plate ended up embedded in the wooden pedestrian bridge, 20-30 ft up.

For the ultimate race car maybe, but how much will that protective plate weigh? It will need to be much thicker than 20guage - the flywheel and clutch of the one I saw went straight through the bonnet!

Gents -

I had my stock 73 flywheel lightened by Reliable Machine Shop in Calgary. They took 6 lbs from the back of the flywheel. I have to admit the driving impressions were not "an order of magnitude" different than stock. I'v had my engine appart and see the previous owner had the rods and pistons lightened and balanced. My engine revs up very nicely but - again - 5 or 6 pounds off the flywheel won't make a huge difference. They charged around $60 cdn for that service.

John Parfitt

David-Would love to see your project if you are in the Seattle area. If your up to sharing let me Know and I will send you my address.
Don K

Hi all,

Another bit of info on this thread !

Just picked up this from RevingtonTR website in the UK.

Under New Products ...

TR5-6 Aluminium flywheel for increased engine response and reliability. Superbly machined with steel clutch face, these weigh 4.2kg. (Standard TR5-6CP weight 9.6kg. CR is 12kg with ring gear) - for later crank.

So a CP weighs 9.6kg

a CR weighs 12kg

and Neil's ally special weighs 4.2kg's which
is roughly a third of the weight of my CR flywheel.

Now thats surely, gotta make a difference ?

With ring gear fitted they are 4.5kg

Sometimes a thread just will not die.

Best Regards


Bob Blewitt

Don Kelly -- I forgot to respond to your last post - Sure , send me your contact info and we can discuss projects and Tr's and enjoy a brew or espresso-
Ah, February --that word has such a sweet ring to us in the Northern Hemisphere-such a warmer word than Jan... But it reminds me that I've got so much more to do to get the TR6 ready for spring driving. Bob B., thanks for the Revington aluminum flywheel update-my stock '75 CF flywheel was 13.2 kg with ring gear installed backwords(as noted earlier this week on the 6-Pack mailing list)-- if you've got your flywheel off note that the lead-in bevel is mounted away from the starter motor teeth, perfect for a Tr3 or 4 --weird.
David Johnston

Now I can speak from experience. My 13# flywheel is great. Does'nt affect idle or pulling away from standstill, but definately improves pickup and overall response Peter G
Peter G

Thanks Peter for your feedback -- the PRI flywheel sure looks like a beautiful piece of work.

David Johnston

I would add, as I tune into my car, that the throttle response on downshifts is instantaneous - I can only attibute this to the light flywheel. I love it. Peter G
Peter G

This thread was discussed between 19/01/2003 and 11/03/2003

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