Torsional Damper

[jon_bailey]

Last time I was out with my boat suddenly developed a vibration whilst cruising. Problem was traced to a 'flywheel' that had come loose from just behind the pulley on the crankshaft. Also lying in the bilge was a rubber gasket approx. 25mm x 3 mm.

Looking through my Clymer manual for a Mercruiser 4.3LX, this flywheel is apparently associated with the torsion damper and I assume that the gasket is also. So I have the following questions:

1) What is the torsion damper and how does it work?

2) Where does the rubber gasket go?

3) How is the 'flywheel' attached to the crankshaft or is it just a friction fit with the the rubber gasket?

None of this is clear from the manual.

BTW managed to get back into Lymington safely after knocking flywheel back onto crank.

All advice gratefully received.



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[Col]

Get yourself a new one before engine shakes itself apart. Don't use it till you have.
ps Try Real Steel in uxbridge.......much cheaper than marine prices

<hr width=100% size=1><A target="_blank" HREF=http://www.arweb.co.uk/argallery/colspics> Cols Picture Album</A>

 

[tr7v8]

Torsional dampers are used to "damp" out the torsional vaibration of the crankshaft. Probabbly the best way to envision it is of a tubular length of say liquorice which you can hold each end of and twist, if this twisting exceeds given limits, either short term or long term the the liquorice breaks. This is the same with certain engines and the outcome is normally a broken crankshaft.
The crankshaft damper is a normal crankshaft pulley with another heavy ring bonded to it with rubber in the middle, this makes the two act as if they have a spring in the midlle.
In the case of your engine which is a V6 then the crankshaft damper does't only act as above it will also have balance weights with it and the flywheel as V6s aren't a naturally balanced layout. The rubber you found was the rubber bonding and the vibration was because the whole engine was out of balance, same as losing a prop blade.

<hr width=100% size=1>Jim

Draco 2500

 

[jon_bailey]

Jim

Thanks for the info.

According to the manual it looks as if the pulley is separate from the torsional damper, i.e. attached by bolts. Can the torsional damper be repaired or should it be replaced as a complete unit?

Also, if the damper contains counterbalance weights, then orientation must be critical so how is it aligned on the crankshaft?

I should be at the boat later today so I'll be able to have a better look then.

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[Col]

You are correct, alignment is critical, so the damper is located by keyway. As I said- Dont attemt a repair, replace it. Jim went into more detail re: balancing, but the long and the short is you need to replace it. Undo the large bolt in the centre to remove complete assembly. (The pulley is usually bolted to damper by 6 bolts) To undo the pulley / balancer assembly-
From the front engine turns clockwise. Use a long socket bar "Knuckle bar" that can be wedged against something solid AGAINST direction of rotation-Block of wood against inside of hull port side would be suitable. Remove coil HT lead to distributor ( so engine won't start ) Briefly "flash starter" for a fraction of a second. This should loosen bolt. Just make sure you do it carefully, and that bar is firmly against whatever you are using as stop. Once bolt is out whole pulley / balancer assemly should just pull of ( a specialist puller is not normally needed ) Be wary of trying to lever it off with a screwdriver or something similar as the plate behind is only preesed steel, and contains an oil seal either of which could be easily damaged.

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[jon_bailey]

After spending the afternoon on it now know a little bit more.

Other name for the torsional damper is 'harmonic balancer' which is a much better description of what it is, i.e. to balance out the inherent inbalance in a V-6 engine.

Have managed to remove all of the bolts but the damper is firmly wedged onto the crankshaft. I've tried to remove using a puller without success yet, due to lack of purchase - but I've other ideas for tomorrow and take your point about the flimsy steel cover behind.

I tried Real Steel for a replacement but they were not sure for a V-6 and they wanted to see existing unit and it's is a long way to Uxbridge. Genuine part is available for £151 + vat.



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