Trigger wheel dilemma on RV8

[richardpope50]

Just seen this post so sorry for the delay so as I have the Griffiths 500 engine ....

Yes, your engine is externally balanced with the crank pulley wheel and the clutch flywheel balanced to offset the crank - the flywheel has similar balancing holes.

No, your trigger wheel is not balanced and what you have to do is measure the offset balance of the pulley wheel, add the trigger wheel and reset the offset balance including the trigger wheel (plus bolts and washers). I got a guy with balancing stuff to do this for me.

Obviously mark where / how it all needs to go back and work out the best location for the missing tooth first as that is where the balancing starts from.

All a bit of a hassle but I was told that on TVR engines the slightest bit of 'out of balance' can easily destroy the engine. I did not take the risk.

My trigger wheel came with my MS kit but I did find a few people that specialise in TVR trigger wheel balancing although I found a local guy in the end. Ask those that sell trigger wheels if they will balance for you as it is a common exercise.

[richardpope50]

I assume TVR couldn't do this as they've ground a lot of metal off the crank to give the longer stroke. Rather than designing a new crank made for the job?

I was told TVR did external balancing as it was quicker, easier and cheaper.

[richardpope50]

PS. Cost me £55

[DEVONMAN]

Just seen this post so sorry for the delay so as I have the Griffiths 500 engine ....

Yes, your engine is externally balanced with the crank pulley wheel and the clutch flywheel balanced to offset the crank - the flywheel has similar balancing holes.

No, your trigger wheel is not balanced and what you have to do is measure the offset balance of the pulley wheel, add the trigger wheel and reset the offset balance including the trigger wheel (plus bolts and washers). I got a guy with balancing stuff to do this for me.

Obviously mark where / how it all needs to go back and work out the best location for the missing tooth first as that is where the balancing starts from.

All a bit of a hassle but I was told that on TVR engines the slightest bit of 'out of balance' can easily destroy the engine. I did not take the risk.

My trigger wheel came with my MS kit but I did find a few people that specialise in TVR trigger wheel balancing although I found a local guy in the end. Ask those that sell trigger wheels if they will balance for you as it is a common exercise.

I'm a little confused, are you saying that some of the original balance weights were removed in order to fit the trigger wheel and then that had to be weighted to compensate.

I can't see how a trigger wheel which is in itself balanced concentrically could otherwise upset the balance.

Regards Denis

[DaveEFI]

I can't remember seeing any obvious signs of balancing on my trigger wheel - like a hole opposite the missing tooth. But it wouldn't be difficult to calculate and do.

But I'm surprised such a small weight so close to the crank centre would make any difference in practice on any RV8. What is it about the TVR engine that makes this critical?

I can sort of see that the crank vibration damper might need critical tuning, though.

[DEVONMAN]

From what I've been told, the TVR 500 crank counter weights are not adequate in themselves to balance the rotating mass and 50% of the reciprocating mass. Just like many Yank motors they put weights on the front pulley and the flywheel.
I have two TVR cranks in use and both are now internally balanced as I didn't have the matching pulleys and flywheels. The extra external forces acting on the end of the crank cause a bending moment couple and this may be a reason why these cranks have a history of snapping. Or that may just be due to the demands of the sporty user.

My trigger wheels have a small hole (6mm dia) opposite the missing tooth which is probably not exactly but near enough.

Regards Denis

[richardpope50]

Pass. No idea why but I did it.