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lightened flywheel,best fixing?


What most of the hot engine builders are doing in your country are adding four more crank bolts for a total of 8. Not sure if many racers here are doing that or not. The 2.5 crank develops some nasty harmonics shortly after 6200rpm that can actually loosen the stock crank bolts.


Luke Skywalker
Hi and welcome!

I'm glad to see you found your way over here to the BCF.

I looked at your photo attachments elsewhere - of the Spitfire you are working on - and must say it looks like loads of fun! That's a lot of engine in a little car!

Regarding the flywheel on that motor, yes, I think Shawn is correct. Now, as I emailed you previously, I have little experience with that particular engine. But in Kas Kastner's books he talks at length about the problems they had with loosening flywheels (and clutch covers) on that motor during it's initial factory competiton efforts. Regarding the TR250 he writes that he was finding a loose flywheel and missing, bent and sheered off bolts all over the place in the bellhousing, after only 18 minutes on the track and that they went through more TR250/6 crankshafts than all the other cars put together. However I have to note that these problems occured with the *stock* crankshafts (and flywheels) he was using.

First efforts to correct the problem included using larger (7/16") and more bolts. Higher torque was then possible. It helped - got them up to 25 minute runs at race speeds - but still didn't totally solve the problem and allow them to finish races.

Ultimately, a key solution was a lightened flywheel, something you are already using. (His setup, along with a lighter clutch cover, weighed a total of 13 lbs.)

The root of the problem was the floppy stock crankshaft being run at high racing revs. They probably found this a bit surprising at first, since the 2L GT6's was strong. However, the longer stroke weakened the bigger engine's crank. The crank's flex set up the harmonics and it moved around so much he described the rotating parts as, "hanging on for dear life", not to mention how it worked loose the bolts on the clutch cover and the flywheel. Kas couldn't do so due to the rules he was racing under, but recommends switching to an improved billet crankshaft as the best solution. That would be best whenever it's allowable. (Which I suspect is more likely now than back when the cars were new. Racing organizations have to be less restrictive as the parts get old and need to be replaced for safety reasons).

Restricted to using the stock crank, Kas says he was able to strengthen it a bit with nitriding.

Canley can probably best advise regarding their particular flywheel and any need to add bolts. In general, extra bolts (a total of 8) are a good idea in any engine that will be revved to race levels, usually with additional locating dowels too. The bolts might be safety wired, as well (although that didn't seem tohelp with the original/stock crank and flywheel, according to Kas).

Additional fasteners are even more important with an aluminum flywheel, where the bolt holes are more prone to elongate in the softer alloy. So, using a lightened steel flywheel as you are, you might have less to be concerned about. Again, check with Canley to see what they advise.

The clutch cover is another issue. Again, considering the changes you've already made, you may not have any problems. A solution for the relatively stock TR250 was to go to larger bolts with partially unthreaded shanks on them, and to countersink the holes in the flywheel a bit, to fit the bolt shanks. That way, the bolts acted as both fasteners and locating dowels. Due to the larger size, I'm sure torque could be increased a bit too.

Hope this helps!



Jedi Trainee
hi and many thanks swift6,and alan myers,(btw thanks for welcome)i asked canley what his advise was regarding flywheel,and he said not to do anything,as it would weaken fly' if it was drilled,and extra bolts fitted,the engine might be developing 180 hp,although i have been informed this will be below 5000 revs.this might increase with dry sump etc.you have given me food for thought,i am very grateful for your time and advice. /ubbthreads/images/graemlins/cheers.gif
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