sbc internal/external. balance flywheel???

Jono FD3 · Post by **Jono FD3** » Tue May 20, 2014 9:59 pm

What's the difference people?? I'm needing a new one, but not sure what's needed!! It's for an old cast block with 2 piece Main seal!

Cheers jono

unstable load · Post by **unstable load** » Thu May 22, 2014 4:55 am

My understanding is that the internal balance of the crank, rods and pistons is for the internal components (obviously) and this allows any flywheel/flexplate to be used. The flywheel is balanced as an individual component and can fit on any engine.
If you choose to you can balance the lot together but you need to remember to fit the flywheel the right way according to how it was balanced to maintain the balance.

DaviesDJ · Post by **DaviesDJ** » Fri May 23, 2014 4:55 pm

Internal balance is when each components is individually balanced - crank with pistons and rods and flywheel and damper individually. This is the better but more expensive way of doing it as a small counterweight crank may require rare earth metal insertion to balance - it is better as the balance is throughout and there is little corkscrew tort ion. External is when the crank and pistons are not in balance but this is compensated for at the flywheel and damper - they are then specific to that engine- cheaper and easier to
Do but a poorer balance as stresses are transmitted through the crank as the balances compensate.

kiwicar · Post by **kiwicar** » Sat May 24, 2014 6:32 am

Hi
internal balance cranks/engines balance up with all the counter weights on the crank, the balance is internal to the engine on the crank. External balance engines have counterweights on the flywheel and damper i.e. some of the counter balance mass is external to the engine.
With an internal balance you can swap the flywheel and damper without re balancing the engine provided they are neutrally balanced.
To check look at the back of the flywheel or damper and see if there is a big counter weight cast into the back of them, you won't miss it! however if you are still unsure stick a tennis ball in the hole in the middle and try and balance it on the ball, if it is external balance it will be noticeably heavier on one side.
best regards
Mike

mr-scott · Post by **mr-scott** » Fri May 30, 2014 11:25 am

One of the most common examples of an external balanced V8 is the 400 small block Chevy, they have both counterweighted front cranks damper and a counterweight that bolts to the back of the crank/flywheel area - easy to find pics of these on a search engine if you need to see an example

Jono FD3 · Post by **Jono FD3** » Tue Jun 03, 2014 10:54 pm

Cheers guys, is there any way of telling by looking at the crank?? Reason being, the block didn't have any pullies or flywheel on when we got it originally!!!

Jono

unstable load · Post by **unstable load** » Wed Jun 04, 2014 6:33 am

The counterweights of the crank will show signs of being drilled or holes having been drilled and filled again, plus possible machining work beyond the clean up at manufacture.
The drilling is to lighten it and the filling in is to add bits of weight depending on what is needed.
Google "balanced crank" and click on Images to see some examples.

kiwicar · Post by **kiwicar** » Sat Jun 07, 2014 6:23 am

Hi
as far as I know all stock 350 cranks are internal balanced, as said the 400 was external and some of the early smaller capacity ones were. You won't have one of those though the mains are different. If you are stuck I have an new un-used cast internal balanced scat crank sat in the garage for £120 if you want it but you would have to come and pick it up from Milton keynes.
best regards
Mike