Twin spark motor woes

[Divano Veloce]

Hmm whats this?

Looks like its coming from no.1 and 2 liners....


Does the 75TS motor have a harmonic balancer incorporated into the crank pulley?

[GTVeloce]

Not that I am aware of however, I noticed your pulley has been cut down. Maybe not well. The original pulley is a triple gang to allow for PS and AC as well as the alternator. I think the extra weight helps with harmonics and balance. If the pulley is even slightly out of balance maybe it is having the effect you are suffering?

[Divano Veloce]

Thats what I'm thinking.... It looks like the standard 75 pulley would foul on the fan and maybe also the radiator crossmember. The modified pulley looks like its been hacked in half.

Although I am pleased with my times at Broadford I'm not so happy with how I treated the motor.... The motor will come apart for a thorough inspection

So the vibration has been sufficient to upset the sealing of two cylinder liners... what else could be affected? The stud on the water pump for the alternator bracket/belt tensioner has been bent over!

The timing is pretty good as I had planned to take the car off the road anyway to repair the body and do a few other bits and pieces like thermo fan and battery relocation and a general tidy up of the electrics.

[Mick A]

4 cylinder engines are internally balanced (crankshaft balancing), whilst V6's are externally balanced (flywheel and front pulley). So I doubt the modification to the front pulley is the cause of any existing issues.

-Mick.

[Divano Veloce]

Thanks Mick, but I don't see how internal/external balance would make any difference; if any of the rotating components change balance then the system overall will be out of balance.

An out of balance pulley would probably cause more problems on the 4 cylinder because of its distance from the nearest supporting bearing... This is still just a theory. Hopefully once its apart something will be apparent...!

[Mick A]

Thanks Mick, but I don't see how internal/external balance would make any difference; if any of the rotating components change balance then the system overall will be out of balance.

An out of balance pulley would probably cause more problems on the 4 cylinder because of its distance from the nearest supporting bearing... This is still just a theory. Hopefully once its apart something will be apparent...!

I know that mate, I already stated that it won't matter on your engine.
I was replying to a previous post if you look back.

[Divano Veloce]

Ok, I gotcha. So in order for this pulley to be the problem it would need to have gone from being neutrally balanced to being significantly unbalanced when modified to single belt.

I've got my old man staying this weekend, he's the one responsible for all of these Alfas (and my general interest cars) so I'm going to make him take the motor out. I've loosened it for him... should be fun!

[john m]

I would have thought that the main cause of imbalance to your TS engine is the flywheel. A 2 litre 105 flywheel was plonked on the crank probably without balancing pulley,crank and FW as a unit. If you ever pull the engine apart have these components balanced together. RE: coolant leaks,  if you intend running the engine don't use glycol in the cooling system. Refill with demineralised water and check if it still leaks. Glycol is not always successful in older engines because of its 'seeping' characteristics.

John

[Divano Veloce]

Turns out it wasnt fun... ended up pulling the motor and gearbox as the two would not separate. They're apart now.... However the head came off with no fuss at all, just slid right off the studs.

So the bearings are a bit funny... all main top halves are good but the bottom halves are all showing normal but localised wear. No. 3 has something very strange going on with some similar marking to the journal. No 1,3 and 5 look the worst....

All big ends are good except for what looks like contamination behind the bearing shells.

Pistons look fantastic except for on the inlet side skirt which is fairly scuffed on all 4.....

As for the balance theory..... The rotating mass as a whole is not significantly unbalanced however the modified pulley is now unbalanced such that it is contributing to/lowering the speed of resonant vibration (critical speed).... its getting excited when it shouldn't...!

[Divano Veloce]

Thanks everyone for listening and for your advice. I'm going to move this discussion into the dormant thread I have for the car.