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This is for a Quattrini kit, the kit is designed to work with 58 x 116 crank. I want to fit 60 x 115. I've got both cranks so cost isn't a factor.

Using a 60mm crank will increase the cc from 210 to 218.

What I'm trying to achieve is to NOT have to use any extra base or head gaskets but gain the extra 8 cc.

I can't quite get my head around the position of the piston relative to the ports if I change the crank.

My (probably flawed) thinking is that the 60mm crank will raise and lower the piston by 1mm at TDC and BDC. Will using a 1mm shorter conrod negate that or will it only affect one of the two?

If you're not familiar with the Quattrini kit it's a small block kit that uses a 68mm piston, this is achieved by not have a bottom spigot on the barrel just a very thin lip to centre the barrel, hence me not wanting to use extra gaskets or packers. Piston is 30mm crown height type so designed to work with 58 x 116 crank.

What is the extra 8cc going to give you?

jonw wrote:What is the extra 8cc going to give you?

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corrado wrote:

jonw wrote:What is the extra 8cc going to give you?

Volume 11.

Copywrite Spinal Tap.

My logical thinking on it is that you might require a 1mm head & base gasket using the 60x115 crank but you might get away with not using any . Dry build is ur best bet

30 mm compression height piston is a constant.

(58 mm / 2 = stroke radius) 29 mm + 116 mm (conrod centre distance) = 145 mm

(60 mm / 2 = stroke radius) 30 mm + 115 mm (conrod centre distance) = [wait for it......] 145 mm

That proves you will not need a head gasket but you will be advancing both transfer & exhaust port timings. Inlet duration will also change but it is a reed valve engine.

A base gasket nominally 2 mm thick will be required.

My guess is that you will now consider a thinner base packer & machining into the head to juggle what port durations you can get.

Head gaskets should never be used as the primary source of sealing IMO. Only ever as a packing around some form of centralising spigot.

Due to increase in stroke and shorter rod it would increase considerably your port timings, and change considerably the characteristics of the kit,, ideally along with the stroke increase and 1mm shorter rod I'd be considering machining around 2mm off the base and adding 2mm to the top of the cylinder.

corrado wrote:

jonw wrote:What is the extra 8cc going to give you?

Volume 11.

Copywrite Spinal Tap.

Thanks for the helpful input gents. I'll have to stick with the standard 58 x 116 then as the work required for the 60 x 115 is above my pay grade.

The Monza I recently built Martin with the 62x110 crank I had to do similar work to get it to work how I wanted, I knew the transfer and exhaust timing durations I wanted, I have a 1.3 base and 3.9mm head packer. It's very good now, very rideable and makes nice smooth power lower down in the rpm range.