22 replies to this topic

[carbon]

If you're wanting smooth engine and are getting it all balanced, then also worth checking that the combustion chamber volumes in the head are all identical. Ideally you want these all to within 0.1cc.

 

And don't assume that a standard or professionally modified head will be to this standard... I have a (well known name) fast road head on the bench and the difference between smallest and largest chamber is 0.8cc (22.2, 22.3, 21.5, 21.8). Pants.

[Cooperman]

If you're wanting smooth engine and are getting it all balanced, then also worth checking that the combustion chamber volumes in the head are all identical. Ideally you want these all to within 0.1cc.

 

And don't assume that a standard or professionally modified head will be to this standard... I have a (well known name) fast road head on the bench and the difference between smallest and largest chamber is 0.8cc (22.2, 22.3, 21.5, 21.8). Pants.

Absolutely right. 

Whilst it is difficult to measure the volumes accurately, it is not too hard to get to within 0.25cc per chamber even with basic measuring kit like a syringe and a sheet of 1/8" thick perspex. Professionals should get to within 0.1 cc.

[carbon]

 

If you're wanting smooth engine and are getting it all balanced, then also worth checking that the combustion chamber volumes in the head are all identical. Ideally you want these all to within 0.1cc.

 

And don't assume that a standard or professionally modified head will be to this standard... I have a (well known name) fast road head on the bench and the difference between smallest and largest chamber is 0.8cc (22.2, 22.3, 21.5, 21.8). Pants.

Absolutely right. 

Whilst it is difficult to measure the volumes accurately, it is not too hard to get to within 0.25cc per chamber even with basic measuring kit like a syringe and a sheet of 1/8" thick perspex. Professionals should get to within 0.1 cc.

 

Thanks Cooperman,

Getting accurate and repeatable chamber measurements does not cost much. I use a digital balance reading to 0.05gram which cost about £10 and a block of blue plasticene from Hobbycraft which was £2. This is a very quick way of checking variations in chamber volume.

PS. Density of the blue Hobbycraft plasticene is 1.65 grams per cc. Other colours also available.

[Chris.Williams]

If you're wanting smooth engine and are getting it all balanced, then also worth checking that the combustion chamber volumes in the head are all identical. Ideally you want these all to within 0.1cc.
 
And don't assume that a standard or professionally modified head will be to this standard... I have a (well known name) fast road head on the bench and the difference between smallest and largest chamber is 0.8cc (22.2, 22.3, 21.5, 21.8). Pants.

Excellent to know, I was unaware.
My head is at the shop now, I'll call him and ask him to verify the cc of each chamber and alter as necessary.
Great bit of info. Cheers

[nicklouse]

AC Dodd has just posted a video on face book showing a really out of balance flywheel.

[ACDodd]

https://m.youtube.co...h?v=bQWBcCKpeeE

Ac

[Chris.Williams]

https://m.youtube.co...h?v=bQWBcCKpeeE
Ac

Great video thanks

[Chris.Williams]

I've called my preferred machine shop, cost to balance is $230 is £133. Including tax.
I will be booking this in.
Thanks for all the advice and opinions.