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TR2/3/3A Flywheels again......

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K

karls59tr

Obi Wan
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From the previous thread on flywheels I learned that the early 3's had the lighter 20lb flywheel and the later 3's... 4's 4A's?? had the 31lb units. Why did Triumph go to a heavier flywheel as the motors are basically the same?
 
My guess would be an attempt to reduce vibration. There were some other, smaller changes with that in mind (like the brace for the shift tower and, briefly, a counterweight on the tail housing). But that's just a WAG. Maybe the later version was cheaper somehow, easier to cast or machine, etc. Or maybe it had something to do with the bolt-on ring gear.
 
During my rebuild, I was unaware of the two different weights for flywheels. I took a sketch I had received from Herman Van Den Akker to my machine shop, indicating where to remove material on the flywheel. They looked at the sketch and my 21 lb flywheel, and said that they didn't think they could remove much of anything from it - so, we didn't. Later, I bought a 2nd engine from a later TR3A and the flywheel weighed 29 lbs. It was apparent that Herman's sketch would have been more applicable for metal removal from the heavier flywheel.

Just thought this might be interesting to some of you.

Pat
 
I had a 29lb flywheel lightened to 24.5lbs from Herman's sketch. I had to have it drilled for the TR6 clutch plate for use with the HVDA, so the additional cost was negligible. I can't say how much different lightening made, since I never drove the car before. I have no issues with the clutch and am sure it is smoother/easier than stock.

Funny you would ask why Triumph would do something... I'm not sure why I do some things.

Jerry
 
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Just a minor safety note. While these things do hold together quite well, on rare occasions they don't. I ran a slightly cut down early 3 model that weighed in at 18lbs. and never had a problem over several years of autocrossing. It was a carbon copy of one used by a local TR4 racer. Until, of course, it let go. He had a scatter shield and after viewing the results so did I, for the remainder of my competition days. So when you start driving that livelier engine and get the bug to get out on a parking lot somewhere, use that ounce of prevention (kevlar maybe). If it didn't have so much junk stored in, I'd post a picture of the hole in the inner side wall of the passenger compartment footwell area of my older car. Produced by an errant chunk of pressure plate, while the previous owner was racing.
 
TRTEL said:
Just a minor safety note. While these things do hold together quite well, on rare occasions they don't. I ran a slightly cut down early 3 model that weighed in at 18lbs. and never had a problem over several years of autocrossing. It was a carbon copy of one used by a local TR4 racer. Until, of course, it let go. He had a scatter shield and after viewing the results so did I, for the remainder of my competition days. So when you start driving that livelier engine and get the bug to get out on a parking lot somewhere, use that ounce of prevention (kevlar maybe). If it didn't have so much junk stored in, I'd post a picture of the hole in the inner side wall of the passenger compartment footwell area of my older car. Produced by an errant chunk of pressure plate, while the previous owner was racing.
Click to expand...

Although I've been following the 2 flywheel threads, I've been staying out so far for just this reason. People are going to do what they want to do, and I didn't want to put a damper on the thread.

I would have no problem playing around with lightening a steel flywheel, but I wouldn't even consider working on a cast wheel. Once you have seen what happens when one lets go, it lessens the need for that extra second or so 0-60mph improvement. Tom's story is a perfect example. It may not happen for some time after you machine it, but cast iron is too brittle and too fatigue prone to trust. Remember the load on a rotating part increases with the square of the RPM. For double the RPM, four times the load. Most of the time a lightened flywheel is used at a higher RPM. It's not just the RPM, but also the number of times you "cycle" the flywheel too. If the engine revs better, you are more likely to rev more frequently and move up the shift point for "fun", which is more fatigue cycles. It all adds up.

And, since I'm started, I also will not personally run an aluminum flywheel without a steel bellhousing.

Steel has a fatigue limit...which is a point of load below which a part will never fail in fatigue. Cast iron is "dirty" steel, in that it contains numerous imperfections internally in the form of irregular carbon. Machining flywheel cast iron can put it well over the fatigue limit in a hurry. Aluminum has no fatigue limit. So, eventually all aluminum parts will fail. That is NOT a mis-statement...all aluminum parts will eventually fail. That is why aircraft receive annual inspections. Racers pull and look at their parts frequently. But, how often does a street car flywheel get inspected?
 
OTOH, if you are looking for safety, you're driving the wrong car entirely. You're sitting in the weakest part of the car, secured only to some rusty sheet metal, with a big steel spear aimed right at your chest and no hint of a headrest to prevent whiplash.

It's true that aluminum does not exhibit a fatigue limit like steel does. But it still has an incredibly long fatigue lifetime. Even at 50 cycles per day, I don't expect to live long enough to reach 1E6 cycles (about 55 years), which is just how long it takes steel to reach it's limit.
 
TR3driver said:
OTOH, if you are looking for safety, you're driving the wrong car entirely. You're sitting in the weakest part of the car, secured only to some rusty sheet metal, with a big steel spear aimed right at your chest and no hint of a headrest to prevent whiplash.

It's true that aluminum does not exhibit a fatigue limit like steel does. But it still has an incredibly long fatigue lifetime. Even at 50 cycles per day, I don't expect to live long enough to reach 1E6 cycles (about 55 years), which is just how long it takes steel to reach it's limit.
Click to expand...

Interesting topic.My guess as to why the change to the heavier flywheel would be response to touchy clutch complaints.The heavier wheel,I presume,was more forgiving at low speed ,start and stop etc. driving.Tom
 
Gouge it during installation or have a bolt come loose in the bell housing and you may not have a million cycles. Slipping the clutch too much can reduce it to the number of cycles on one hand. Don't get me wrong, I'm not at all saying not do lighten or run an aluminum flywheel. I'm just saying it has it's place, and my 50 year old street car is not that place...for me.

And I agree, Tom. A heavier flywheel makes stop light driving much easier and smoother.
 
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