The V8 Owners Forum -

I've been told that I cannot fit a trigger wheel to my 5.0 TVR V8 engine as it is probably externally balanced.

My question is; is there a way of knowing for sure that the engine is externally balanced? and if it is, is there another way of mounting a crank position sensor?

Trigger wheels are normally balanced anyway so should have zero effect on any balancing on the engine, there is normally a hole drilled in the trigger wheel opposite the missing tooth to make the wheel "balanced".

I strongly doubt that a trigger wheel will induce very much vibration in any V8 installation but I am sure there will be someone with more knowledge along shortly

V8aholic wrote:I've been told that I cannot fit a trigger wheel to my 5.0 TVR V8 engine as it is probably externally balanced.

My question is; is there a way of knowing for sure that the engine is externally balanced? and if it is, is there another way of mounting a crank position sensor?

A properly made trigger wheel (Trigger Wheels, etc) is balanced. It will normally be a tight fit to the machined shoulder on the pulley boss, so will also have no run-out. Which only leaves the fixing nuts and bolts, if they need to be changed.

Who told you one couldn't be fitted?

I'd also hope any crank etc is dynamically balanced. Which means along its length - not just via one point like the crank pulley assembly.

I was told that the reason I could not fit a trigger wheel was because the engine may be externally balanced (apparently this is what TVR did).

I really would not have thought that a trigger wheel would have enough mass to cause a significant issue either, but that is what I was told by a very reputable Rover specialist.

I'm hoping to fit a quad throttle body and management system, but without a trigger wheel I can't even get started.

Wasn't RPI, was it?

Yes some 5.0 TVR were externally balanced and had a dedicated front pulley and flywheel. I had mine internally balanced by Real Steel which required some Mallory metal put into the counterweights of the crank.

A trigger wheel will not affect the balance provided you do not remove any metal or weights from the pulley,

Regards Denis

Whoever said it, hit them a slap.

Unless they're using very large and heavy trigger wheels with odd shapes.

But for any sensible normal trigger wheel, it wont pose any problems at all.

Here's a pic of the damper on my engine...



There are a few blind holes drilled (circled red). Would this mean that this particular 5.0 is externally balanced?

I agree with the comments on here - how could a trigger wheel upset the balance. Maybe the engine builder was just trying to talk me into having the engine internally balanced (at extra cost of course).

What would be the benefit of having the engine internally balanced?

The standard damper on my SD1 has obvious balance drillings too. Not surprising given it's a rough casting or whatever.

Thing is, it is rubber mounted on the boss. So must move at least slightly relative to the crank. Therefore not an ideal place to balance anything else in the chain.

The explanation I remember reading somewhere is that dynamic balancing tries to make every part of the chain in balance. If you were to slice it into bits, each bit would be in balance. Now obviously, you can't do this with a crank, so you try to do it in sections to retain the principle. So basically each big end/rod and piston combination should be individually in balance.

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?

The safety ring behind the damper may have weights pinched into it and to put a trigger wheel behind the damper may necessitate removal of this ring and hence upset the balance.

Regards Denis

There are lots of variations of RV8 crank pulleys, but on my air con SD1, I could fit the trigger wheel either behind or in front of the damper. A bigger problem was the sensor mounting - it had to be specially made. The ready made ones might fit a Range Rover, but the steering pump is in the way on an SD1.

There's always room for a trigger wheel somewhere, it shouldnt be difficult.

Likewise a sensor.


Adapt and overcome.

Yes. But I bought a trigger wheel kit for an RV8 and didn't expect to have to fabricate bits.

The engine in question here is an interim serp engine and the damper is very close to the cover and not like an SD1 where the damper is much further out. I have fitted a trigger wheel behind the damper on my interim serp engine but there is then no room to also fit the safety ring, ( the item coloured greenish in the picture). If this safety ring has the balancing weights fitted by TVR then the ring needs to stay in place and the trigger wheel then put on the front of the damper. This will of course move the belt drive pulley forwards about 10mm which will need the water pump pulley and alternator pulley needing to be spaced forwards also together with any other item driven by the serp belt.

Warning, if the trigger wheel is put on the rear of the damper, the heads of the six retaining bolts will be very close to the oil gallery of the cover, so do not put the bolts in from the front with thread showing beyond the nut on the rear ,
Regards Denis

Depending on the thickness of the trigger wheel, which could be as thin as 2-3mm it shouldnt be hard to find room.

The photo does look tight at the rear, but one could easily be machined and then affixed to the front section of the pulley that is photographed, without affecting where the belts run.

Obviously it will require a little fabrication, but it wouldnt be that hard.

Presumably it is for an aftermarket management system ?

If you were really really really really really really stuck.

You could just use the dizzy as a trigger to run an aftermarket system, but really a crank trigger would be best