v8 crank sensor / balancing

[hiltonig]

Chaps,Just putting toghter a parts list for a forthcomming 5.4 build and have a couple of questions.

1. I have the crank and need a crank sensor cog /gear thing, where do i get one and does the crank need to be balanced with this on ??

2. I have seen a SFI harmonic balancer, anyone fitted one on a road going car , just wondering


Thanks for your replies

[Speed eight]

Hello hiltonig.
The crank sensor, should it be balanced.
This depends upon a few points.
If the engine is already built and the mass of this item is very small, a few ounces, then because it is so close to the centre line axis of rotation I see no point in tearing the engine apart just to do this.
If the engine is not yet built, then yes include it in the balancing.

The SFI, SFI Foundation Inc. of America, sets certain standards for Automotive street use and racing products.
One of these being Harmonic dampers.

The products which carry this qualification are accepted as being of a very high standard throughout the Automotive industry.

Do you need one to replace your existing damper?
This will depend upon a few things.
Is your existing damper damaged or do you not have one?
If the money is of no consequence, then fit one.
Will you derive any benefit from it over the standard item, possibly not.

If your standard damper is to be spun at a speed which exceeds its normal capacity then you will need to change it.
Dampers do have a maximum working revolution speed.
Often this is some speed above the range in which they are used.

Also many different types of dampers carry the SFI rating. So now you are into which "type" of damper to choose.

For ordinary engine Rpm range and street use then the standard manufacturers damper should be fine.

Regards,
Speedeight.

[2Munkys]

hiltonig said:

Chaps,Just putting toghter a parts list for a forthcomming 5.4 build and have a couple of questions.

1. I have the crank and need a crank sensor cog /gear thing, where do i get one and does the crank need to be balanced with this on ??

Thanks for your replies

I guess all that Speed eight says. I think my trigger wheel came from Mech Repairs (01242 243385). So that it could be fitted, if I remember correctly, a balance weight had to be machined from the rear of the pulley. That value had to be reinstated after the trigger wheel had been fitted so I sent the pulley/vib' absorber assembly to 'Power' to carry out the work of assembly and dynamic balancing.

Incidently, I'd been told that adding a 40 gram wheel-balance weight to the inside of the pulley skirt would be about the right correction; that turned out to be 'way off' what transpired. The only reason this was all neccessary was because 'Power' balance their cranks/absorber/pulley/flywheel as an assembly; possibly not your case. V8D put my 5.4 together and as I understand it, the constituant parts are all balanced to 'zero'.

[hiltonig]

hey thanks for the replies, yep this is a new build and the crank inst balanced yet, I have been told the balance the crank serperate to the new flywheel.

Its a new build and although its for the road I want the best i can fit, I see realsteal sell the sfi harmonic balancer

Thanks for the replies.

[TVRleigh_BBWR]

I've just fitted a trigger wheel to the late style front end of a Rv8 that has a harmonic Balancer.

See pic's below.

I'm taking the crank, Lightened Flywheel clutch rods pistons and pulley etc, to a balancing company tonight. so I'll let you know what they say.

[Mark Adams]

The standard serpentine pulley carries a balancing skirt behind it, which must be removed to make space for a trigger wheel to be fitted. For all TVR engine sizes excluding the 5.0 Litre there are not normally any weights in the circumference of the balancing skirt, so it can be removed with no problems.

However the exception is the standard TVR 5.0 Litre motor which is externally balanced, meaning that the crankshaft is not naturally balanced (due to the size and placement of the counterbalances). Weight is added to the crankshaft pulley (in the back of the balancing skirt), and removed from part of the circumference of the flywheel to provide balance.

For this engine the flywheel, pulley and crankshaft are all a matched set and must stay that way!

Therefore if your balancing skirt has a balancing weight in it, it will need to be measured. The same correction is then applied to the pulley without the skirt on, in order to provide the same out-of-balance force. Typically the weights range from 57 grams to over 100 grams. John Eales Developments, TVR Power, or V8 Developments can do this for you.

Out of interest, this is probably a factor in the occasional 5.0 Litre crank failures, which nearly always snap on the web behind the pulley.

Since you are building a 5.4 Litre motor, you will undoubtedly be using a new crankshaft which should be naturally balanced. Therefore you shouldn't have the problem.

John Eales Developments can supply alternative dampers, and beautifully made crank trigger kits too. That's what we use when fitting Omex systems.

[TVRleigh_BBWR]

Got My whole set-up balanced, rods, pistons, crank flywheel, clutch cover and pullie with trigger wheel,

They did need to do some balancing on the pullie and wheel metal was taken off both. but not much. they also removed the lead weight.

[rev-erend]

I bought one of the John Eales damper assemblies : pictures here :
http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

It comes fully balanced.

When TVR balanced the pulley / crank and flywheel - as Mark said it was done as a whole. No each item done seperately. This method is much cheaper to do ..and is OK until you change of alter any of the components..