Crankshaft or flywheel/clutch damper

[2cams70]

A properly built Ford Kent engine should not vibrate at 4,800 RPM. 4,800 RPM is well within the design parameters of the standard engine. Something else is wrong. It should not take a tortional damper to fix it.

[vstibbard]

All thanks for the many contributions, as per my initial post the issue starts at 4800rpm and remains as rev's and road speed increases. the primary changes the original engine was replacement of OEM flywheel with new light weight 4 bolt version at time of rebuild and use of modern Tilton single plate clutch so all much lighter, all were dynamically balanced before assembly. I'm interested whilst part in removing all potential contributors,

We di following:
1. isolated tyre balance by initially rebalancing all wheels and tyres then changed to a spare set of wheels, and rebalanced. Issue remained, note the CR65 tyres are used..
2. Changed differential mounts and diff tie rod mounts for softer and urethane type ones and splits appearing. What do UK racer use?
3. We carefully re-phased proposal shaft joints based on modern practice, the TTR propshaft was reconstructed by a V8 Supercars drivetrain specialist which improved balance and offset the uni joints by a few degrees.
4. As the engine is drysumped and mounted as low as possible together with S2 26R chassis which raises the diff by 1/2", we carefully measured angles of engine/gearbox alignment and made jigs to align engine/gearbox to diff to everything was within acceptable uni joint angles based on modern practice.

What remains to be tried is from our view:
a. new engine with DKE 8 counterweight crank, flywheel, arrows rods, lightweight forged pistons, question is with or without damper? easier to engineer and fit this while reassembling.
b. Engine mounts to stiff, we used Kelsport small bush Group 4 mounts. we did not get to change these over due to accident. We will change these to either filled in standard engine mounts next time or the road type kelsport Group 4 type with larger bushes for more compliance. Any feedback from other racers would be appreciated as to which engine mounts are typically used would be appreciated.
c. tyres that are out of round as its not apparent on when balancing wheels, will check these, likely result is to change to Avon Formula Ford tyres or Avon CRZZ.
d. balance of S2 type sliding spline axles, but the rotating speed is not high.

Any other suggestions?

Regards

Vaughan

[rgh0]

I use standard diff mounts and rear gear box mount. Use TTR competition mounts for engine. These engine mounts transmit more vibration at idle and low revs but not at high revs.

regards
Rohan

[2cams70]

It still has not been isolated yet whether this is an engine or a transmission/driveline problem. Unless it's first identified either as being either way we are really only chasing phantoms.

Although I have not used it myself I've seen a few professional OEM automotive engineers using this App to analyse roughly in field vibration problems. Maybe it could be used here too with the engine run up and down the RPM range whilst in neutral:

https://itunes.apple.com/au/app/vibrati ... 85888?mt=8

Note I would normally expect a light weight flywheel to reduce torsional vibrations. You usually get torsional vibrations when you have a long and therefore twistable crankshaft with a heavy flywheel at the end. If it's a torsional vibration at 4,800 RPM (which I highly doubt) you should also feel a lesser torsional vibration at 2,400 RPM. How well done was the dynamic balancing when the flywheel was changed?

[Bigbaldybloke]

Just a suggestion, get the car up to the speed when it is vibrating and knock it into neutral and coast. If the vibration stops it?s engine if it continues it?s transmission.

[nmauduit]

It appeared around 4800rpm and got progressively worse, was not apparent in 1/2nd gear.

short of a decisive lead, this stroke me as a specific clue - unless it is just that the vibration was somehow not noticed in 1st/2nd gear - did you investigate in direction of the gearbox itself?