Shaft extension for fan - retrofit Kenlow

[Moliver]

Hello All,

I have made a mistake and have bought a TR book. It says, that the crank extension shaft for the ventilator should remain when fitting a Kenlow and removing the fan as the shaft extension has the function of a balance weight. Is this correct?

Advise welcome….

Cheers

Oliver

[RobH]

1 minute ago, Moliver said:

the crank extension shaft for the ventilator should remain when fitting a Kenlow and removing the fan as the shaft extension has the function of a balance weight. Is this correct?

Not really Oliver. There is some speculation that the fan extension may act to damp torsional vibration in the crankshaft but it is no more than speculation as it certainly wasn't designed to do that, and it's difficult to see how it could. Many people have removed it with no detriment.  

Quote from Revingtons     https://www.revingtontr.com/tr4/faqs/tr-notes-and-queries:

Q: Does the 4 cylinder TR engine require an harmonic balancer on the front of the engine?

A:The subject of balancers needs careful consideration. You can be sure that when BMW specify a harmonic balancer for a new engine they don't have an engineer thumbing through a catalogue over a cup of tea looking for one that might just fit- sort of - if modified a bit. It would be more realistic to assume thousands of hours of testing goes into the design for each application.

RevingtonTR have close contacts with a vibration specialist company who have designed a suitable damper for 4 cylinder TR use but agree with us that this only has a primary value above 5000 rpm. We use this damper when we install a billet crank into an engine that will reliably and continually run at 7500rpm. The company in question do work for Bentley so I think it is fair to assume they know what they are talking about. This damper needless to say is intended for use only where the engine fan has been removed. 

By contrast Neil Revington's TR2 has no damper on the front of the engine. This engine uses a standard crank and rods and has been used in competition and on the road for over 200,000 miles, much of which will have been at high revs, up to 6500 at times. It suffers no vibration and the engine is as smooth as the day it was built. Neil designed our aluminium pulley over 20 years ago which has been fitted to hundreds of engines built for road and competition use. We have had no complaints of torsional vibration that would need eliminating with a harmonic balancer. Coupled to this we have sold many hundreds of thin fan belt conversion kits incorporating out aluminium crank pulley all over the world with no negative feedback about vibration. Most of these kits are sold with an electric fan indicating their use without the engine fan fitted. It is naive to think the fan fitted to the front of a 4 cylinder TR engine is in some way a damper. The fan is a crude device and its design and the manner in which it is attached to the engine gives no suggestion of it having any anti vibration design intent.  It is interesting to consider that the TR250-6 fan is mounted on its crankshaft with an harmonic damper using the exact same part number small rubber bushes that TR's 2-4A use reinforcing the conclusion that they are there to try to prevent vibration being introduced by the fan, not as some form of harmonic balancing of the engines internal components.

[john.r.davies]

It is exactly this question that I can answer, by applying my analysis of of torsional vibration in the crankshaft that I have developed for the T6 engine, to the T4.   But I need a willing owner, to let me fit sensors, removable sensors, to their car and take readings.

See my article in TR action for details of the T6 work. Issue 320 - Mar/Apr 2020, Page 41

Volunteers form an orderly queue, please!

John