12 replies to this topic

[mjpuds]

as heading says just built up engine 1380 been running it in over last month all done now ..but i ran out of time and fitted my old flywheel from my last build...so wish i had balanced flywheel to crank..i am thinking there is a little to much vibration..for my liking ..anyone else had issues like this..

 

 

[Captain Mainwaring]

as heading says just built up engine 1380 been running it in over last month all done now ..but i ran out of time and fitted my old flywheel from my last build...so wish i had balanced flywheel to crank..i am thinking there is a little to much vibration..for my liking ..anyone else had issues like this..

 

 

 

The whole lot should ideally be balanced as an assembly. If you fit a flywheel from an assembly that has already been played with, that flywheel could be all over the place in terms of balance.

[mjpuds]

Bit late now...bugger

[KernowCooper]

How much vibration do you have ? there are lots of 1380s running standard out and about not balanced, what sort of revs is it at? I had my 1330

flywheel.crank and clutch done as a unit.

 

If you not revving it to death and it does not feel smooth in normal driving you have a problem somewhere.

[mjpuds]

more than my last engine but that had a softer cam ..276..this has a 286.. 1.5 rockers .. when revs kick in it smooths out a bit ..but with nothing to base it next to it tricky..

[Jordie]

are we talking vibration due to unbalence?

 

or vibration, due to higher idle / lumpy idle caused by the cam (286). Whats your idle speed?

[jaydee]

you should feel it vibrating at about 3k rpm if not correctly balanced

[Cooperman]

With a 286 you will be needing to use around 6700 rpm to get the best driving performance and a full rotating assembly balance is absolutely vital.

[Captain Mainwaring]

you should feel it vibrating at about 3k rpm if not correctly balanced

 

From what I understand, the 1275 crank will resonate at between 5950 and 6250 rpm......obviously there are sub harmonics too.

[jaydee]

Thats why it resonates at 3k rpm...

[mjpuds]

Now heres a question if I bought a lets say med or similar ligthened balanced flywheel backplate and cover ..and swapped it over would a lightweight kit make this less noticeable. .

[Cooperman]

Not really. The bottom end must be balanced as a unit or it will not be balanced at all.

If running a 286 with the rev range necessary to make it worthwhile fitting it, then a full balance is essential.

[Captain Mainwaring]

Thats why it resonates at 3k rpm...

 

Thankyou - I'd never managed to work that out. 

 

Balance and resonance are two different things though, as I'm sure you know.