Valve to Piston distance

[fjbm]

Hi

I'm planning to keep the type C pistons and the big-valve head but using the Burton's BL46 cams, with 280? and .380" lift.

Will this be possible?

Thanks

[bcmc33]

I'm planning to keep the type C pistons and the big-valve head but using the Burton's BL46 cams, with 280? and .380" lift.

Will this be possible?

You need to ask Burton for the full technical details of the cam operation. They should supply you with the crank angles at which the inlet and exhaust are fully open and the corresponding inlet and exhaust vale lift at TDC.

The probability is that the inlet clearance will be OK but the exhaust could be a problem.

On my engine stripped-down recently there was evidence that the exhaust valves had been touching the pistons with cams at 0.35 lift. Both cams had offset dowels so it was not clear as to the expressed period angle.

The andyhodg post (elan-f15/valves-contacting-piston-crowns-t20065.html) shows how close it could be - but he did not say what cams he was using. I guess the easiest option is to machine the exhaust cut-out a little deeper/wider.

[gerrym]

Dave Walker has some good advice on this subject (refer to his book on Tuning etc). He writes for one of the Performance & Modification magazines, plus the Emerald connections. He has recommendations on the difference between static and dynamic piston to valve clearance (or how much to allow). I mention this because as part of his rolling road tuning sessions, cams are swung but before this can be done on an interference engine, one needs to know what the internal clearances are (as a function of crank and cam angles).

Using modern technology, it must be possible to get some comfort from a trial build of your engine (ie without gasket preps, etc). Even one piston/conrod/inlet/outletvalve may be sufficient so long as you consider the component tolerances for the rest of the cylinders. Consider using a endoscope through the plughole and/or some plasticene squashed into the valve cutout. 9mm OD is a pretty common size. Endoscopes are much more commonly available now and within the cost affordable realm of the home LTC builder. Or hire one. You will get a witness mark on the plasticene and this will tell you how much clearance you have.

Regards