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TR2/3/3A Lightening a stock TR3A flywheel.....

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karls59tr

Obi Wan
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I have to pull the gearbox to change out the clutch and get the flywheel resurfaced. I was wondering about lightening the stock flywheel.I don't want to go to the expense of installing an aluminum flywheel and I do know a machinist that would do it for a reasonable price. I was wondering if anyone had any information as to where to drill the flywheel and how much to take off etc. How would a lightened flywheel affect performance and what would I have to adjust in terms of retuning the engine?My 3 has a rebuilt motor, Petronix,a header,mild street cam,stock SU's,4A intake. Is doing this worth the effort or am I wasting my time for a small gain in performance?
 
Karl
I just had my flywheel lightened by 7 lbs. That was the most the machinist thought was safe. My engine sounds similar to yours except I have the Moss Supercharger. The extra zip is worth the expense. The machinist had to enlarge the hole at the center of the flywheel to mount the flywheel on the lathe. I gave him the pressure plate and let him do the layout. For the amount of cost ($250) I think it is a lot of fun for the buck.
 
Here's a photo that might help


That's a billet steel flywheel (from ARE), rather than a cut-down original, but it shows the areas that need to be left and the ones that can be removed.

I have a Fidanza aluminum flywheel on my TR3, which at 10 pounds is much lighter than you can take the stock cast iron wheel (without risk of having your feet amputated anyway). I didn't make any special changes to the motor, but note that you want good low end torque or the car will be harder to launch. The engine in my TR3A didn't pull so well at low rpm, and it was a bit of a learning experience not to kill the engine when driving casually. The motor in my current TR3 pulls better below 1500 rpm, and I've still killed it once or twice.

I see the Fidanzas have gone up since I bought mine some 20 years ago, but still only $310 at Amazon. For $60 more, I'd still go that way. But note that the Fidanza comes drilled only for the TR4A clutch. You'll need to either use a TR4A pressure plate, TOB & carrier to match it, or have it redrilled for the earlier clutch. I went the TR4A route, as it is also lighter than the stock TR3-4 clutch.
 
JerryVV said:
I believe there are instructions as well as a drawing in one of Kas Kastners Competition books.
Click to expand...
I was just looking for that, with no luck. If you happen to remember which one, please let us/me know.
 
Ah, OK, I found that passage in the 2003 version "Triumph Preparation Handbook", page 121. No diagram though, and the photo shows a lot of work that wasn't done on a lathe. The original factory TR3 & TR4 "Competition Preparation" manuals (which were also written by Kas Kastner) just say to use aluminum.
 
tinman58 said:
Karl
I just had my flywheel lightened by 7 lbs. That was the most the machinist thought was safe. My engine sounds similar to yours except I have the Moss Supercharger. The extra zip is worth the expense. The machinist had to enlarge the hole at the center of the flywheel to mount the flywheel on the lathe. I gave him the pressure plate and let him do the layout. For the amount of cost ($250) I think it is a lot of fun for the buck.
Click to expand...
Where did your machinist remove the material from the flywheel? One of the replies to my question led to what Kastner said on the topic..."most weight is taken from the outside and on the cylinder block side"....not sure what is meant by the outside?
 
I interpret this to mean that most of the material was removed close to the outer diameter of the part as opposed to close to the center.
 
Last edited:
TR3driver said:
Here's a photo that might help


That's a billet steel flywheel (from ARE), rather than a cut-down original, but it shows the areas that need to be left and the ones that can be removed.

I have a Fidanza aluminum flywheel on my TR3, which at 10 pounds is much lighter than you can take the stock cast iron wheel (without risk of having your feet amputated anyway). I didn't make any special changes to the motor, but note that you want good low end torque or the car will be harder to launch. The engine in my TR3A didn't pull so well at low rpm, and it was a bit of a learning experience not to kill the engine when driving casually. The motor in my current TR3 pulls better below 1500 rpm, and I've still killed it once or twice.

I see the Fidanzas have gone up since I bought mine some 20 years ago, but still only $310 at Amazon. For $60 more, I'd still go that way. But note that the Fidanza comes drilled only for the TR4A clutch. You'll need to either use a TR4A pressure plate, TOB & carrier to match it, or have it redrilled for the earlier clutch. I went the TR4A route, as it is also lighter than the stock TR3-4 clutch.
Click to expand...

I have had a Fidanza on my TR6 for several years. I thought it was closer to 9 lbs but may be wrong. It is great at low end and acceleration and impressive in the mountains (in the East or West) on up hill grades even pulling a trailer. I agree with Randall's comments. Although I haven't had problems stalling my 6.
 
The original tr2 flywheel tipped in at 23 lbs, the tr3 at 32 lbs .If you can lose
9 or 10 lbs it is nice.The tr2 unit had a lot of metal off the engine side and was a little
weaker.I like the off the perimeter approach as in the picture. It saves rotational inertia
which is the real issue.When you do this , it should be balanced to the crankshaft it will
be married to.....
MD(mad dog)
 
Here is a drawing I made from a sketch that I got from Herman van den Akker. I plan to install his HDVA conversion in my restore project. His kit requires the TR6 pressure plate so the stock flywheel has to be re-drilled to fit it.

Bert TR3 Flywheel Dwg.jpg
 
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