Hitchcocks Forum

Chaps



Me again with a (possibly) silly question.



Before I get the frame powdercoated and the tank painted, is the 612 converted engine 'taller' than the standard unit, as the clearance from the tank to the (specially turned down) rocker cover nuts is already marginal.



Thanks in advance.

Yes Johnny about 6mm from memory I had to fit a shorter stud in the rear rocker cover to be able to remove it

it depends if you use the compression plate that comes with the kit and no second gasket

then its 3mm.



i you use the 2mm plate, its advisable to use (lot)higher octane fuel

or they will here you pinging in the next town

even with the 3mm plate and second gasket, you’ll be on te edge of starting to ping.



adding a second gasket wil ad about 1mm.

the second gasket is the one between the plate and cilinder.

if a second gasket is not used, a silicon sealant is necessary.

Hi Johnny,
There is one stud at the rear which the rocker cover will not pass over unless the stud is removed first. I overcame this by getting a plain nut the same size and cutting through one of the flats with a hacksaw, so that the nut can be "pinched" onto the stud threads with a molegrips in order to remove (and also to replace) the offending stud. I suppose the stud could be replaced by a bolt, but I am not a fan of this method (as studs better preserve the integrity of the threads in the head). While on the subject of the 612, I have found that a total stack of 6mm under the barrel works best in my engine in order to avoid detonation and I would advise anyone else contemplating these fine conversions to do the same (that is: 1 x 3mm plate, plus 1 x 2mm plate and 2 base gaskets). And the rear rocker cover will just about clear the frame tube when the stud is removed as described.

Thanks Chaps



Removing the rear rocker cover is already an engine out job, on Slo Poke, but it looks like I'll be into relieving the fuel tank in places - maybe even locally modifying the frame.



Hmmmm.....food for thought.

OK .



So we've tried raising the front of the tank by about 8mm and the taller engine will nicely clear the tank - and the engine will clear the frame, so that's all good.



Is there a general consensus concerning Barry's suggestion (ie 1x 3mm plate, 1 x 2mm plate, plus 2 gaskets)?

Johnny, tank was not the issue the issue is you can't lift the rocker box because of the frame I can't remember which rocker box stud was the issue but all I did was fit one of the shorter studs, drilled the rocker box down to the same depth as the 2 side ones and used 3 of the long rocker cover nuts and the problem was solved, the extra height was no longer a problem

Hi Norm



As I mentioned, Slo Poke's frame is non standard so the engine sits slightly closer to the top-tube than standard and, obviously, this means that the tank is also a little lower:








I probably will drill the rocker covers, as you suggest, but remain curious as to any consensus concerning Barry N's use of packing pieces and gaskets.



PS. I should probably point out that I don't always ride in plus fours, while smoking a pipe, but do on the Distinguished Gentleman's Ride.

playing around with different thickness of plates and adding gasket will get you there in the end, but. .



as each engine is different so is each solution.



some engines runs with 3mm plate and 3 gaskets, some need more.

different things come in to play with this.

cranking compression, max advance ignition, …………



when building a 612 i personally i don’t use our host high compression piston any more.

not that is a bad one, its more competition orientated than road use.

i use the egly touring piston, witch is a good compromise for the road.