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Big cams in a twin

G

GregT

Forum Sage
A word of warning for those who want to go full house with a twin - 450 or 500, 2V per cylinder specifically.

My race 450 came back to me recently after a period on loan. I went into it to service it, and found one cam cap lifted with broken bolts - and a broken camchain tensioner blade. Although the camchain was slack, nothing had hit - and it was still running pretty good.

The broken blade is peculiar to the manual tensioner i was using and I've adressed that problem.

The broken cap bolts however could arise again as each cam is only held down by four 6mm bolts...i'm using the max cam i can without going to shim under bucket - around .415in lift. i'm not using excessive springs either - approx 75lb on the seat. this is enough to let it rev to 11 plus.

I'm obviously going to watch for this - and if it happens again, there is enough room to retap to 8mm...
 
Last edited:
I have seen cam caps lift and break the bolts when the bolts were too tight. You can stress/stretch and crack the bolts with too much torque. When the cams add more stress they will break.
 
rapidray said:
I ran MUCH bigger cams in the 500 we raced & never had an issue.
Ray.
Click to expand...

Fair enough Ray - the 500 is of course much younger than an early 450...bolt age/life may well have something to do with it. These were not overtorqued either.
It may be a wise move to simply replace with new bolts....
 
It could have been stressed by a previous owner. I have broken the bolts off removing them. They break where the shoulder meets the thread. The rest of the bolt came right out without drilling, I just used a pick to back them out.
 
What sort of cam's do you run in there Greg? Something from another model or fancy you-beaut race cam's or something?

I'm contemplating sticking some GS500 cam's in my 450 for some extra lift and a touch more pep up top... don't want anything too fancy for a daily rider!
 
pete said:
What sort of cam's do you run in there Greg? Something from another model or fancy you-beaut race cam's or something?

I'm contemplating sticking some GS500 cam's in my 450 for some extra lift and a touch more pep up top... don't want anything too fancy for a daily rider!
Click to expand...

These are a Lotus Ford profile from a local cam grinder. There are literally hundreds of profiles for the 4 cyl Fords and the follower dia is pretty much identical to the GS setup so they're very useful to us.
I'm unsure as to whether 500 cams are significantly different to the 450, sorry.
 
GregT said:
I'm unsure as to whether 500 cams are significantly different to the 450, sorry.
Click to expand...

The difference I've been able to find is only in the lift and by only 0.04mm. Maybe there is a difference in duration.
 
Thanks for the clarification Greg, I'm not quite that keen for my daily rider :)

I have looked through the factory manual for the 450 and can't find duration either... so we still don't have the duration numbers as yet.
 
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