Piston clearance on old school pistons

[greg brillus]

Does anyone remember what amount of clearance you were running on old school race pistons...........A mate of mine is rebuilding a G 45 Matchy racer..........Not sure why he wants to run the old type pistons other than he is too stingy to buy something more up to date..........these engines had a 66 mm bore size, and I believe the pistons have a split skirt as well.......... Personally I would leave them on the shelf.........any idea's..........Cheers........ Greg. PS: This engine will most likely be running on methanol fuel.........

 

[Peter Holmes]

I would be more worried about the crankshaft.

 

[timetraveller]

From memory about two thou per inch of bore diameter on the for and aft faces. More at the sides as the pistons should be 'cammed'.

 

[bmetcalf]

Vibrac, didn't you race one or am I confusing with your 7R?

 

[vibrac]

G45! I once bought one for £120 but thats a long story I may have told before
It was £80 part exchange for my G3L, but mum was told it was a 'Racing' bike so I had to settle for a 7R at £50 (another 350!)
my mate got the G45 a good year on the road for both of us (not for racing) rave of the coffee bars
I still say the best looking bike I have ever seen.

 

[BigEd]

Vibrac, didn't you race one or am I confusing with your 7R?

Roger Ashby raced a 7R and I think also ran a G45 a few times in Vintage race meetings years ago. He also had a go at the challenging Manx GP Classic race with the G45. I think the I - o- M circuit won.

 

[Sakura]

I would be more worried about the crankshaft.

I think the nodular crankshafts are pretty bulletproof as long as the radii are correct.

 

[Albervin]

Sixty year old pistons with split skirts running on methanol. What could possibly go wrong?

 

[Peter Holmes]

Sixty year old pistons with split skirts running on methanol. What could possibly go wrong?

Shame George Brown isn't still around to tell us.