I am in the process of stripping down and reconditioning the cylinder head on my 1960 350cc clipper. Can anyone tell me, with the barrel and piston installed and the piston at T.D.C how far above the cylider/barrel top “collar” does the top of the piston body protrude. I have attached a link that shows a piston body flush with the cylinder top collar. In my case, the piston sits 2mm (.078”) above the barrel ring! The previous owner rebuilt the barrel,piston and bottom end with the following hand made parts: barrel gasket, is a 2mm aluminium plate which when installed highers the barrel so the the piston body is flush (as in picture) He again made a cylinder head gasket from 1.54mm (.061) aluminium plate (cut & shaped to head gasket) both plates had gasket glue applied. Sitting on top of the cylinder/barrel collar is the copper ring (2.02mm (.079”) which is a head gasket for a 1957 350cc Clipper! I have been told that my piston specs are correct. The bike was running fine apart from burning oil due to badly worn valve guides hence the strip down. Any comments would be appreceated Thanks Stuart
Stuart, Ultimately, you want a compression ratio suited to the fuel available. Since the top end has been disassembled in the past, and a thick compression plate added to the base of the cylinder, you might wish to check if the barrel has been shortened, or the head shaved, to compensate for the extra barrel height relative to the piston. It does not take much metal removal/addition to change the compression ratio. That does not answer your question, I know, and only adds to the complexity. A 1959 Clipper 350 engine lives here, #774, but I do not wish to disassemble it. I wonder how many of this model survive to compare. The Pashley trike, also sold in the USA as the Indian Patrol Car, uses the same engine, if that widens your prospects to compare. (My example came to me with an Indian badge on the timing cover. If original, it means the engine is from a Patrol Car, but the factory records have strayed and we may never know. If it had come with a gearbox that would have been an indicator, as it had reverse.)
Yes, since your engine is a bit of an unknown quantity, the usual trick here is to lay a thin band of something like plasticene over those valve cutouts in the piston, completely assemble the engine and turn it over a few times, dis-assemble and examine the plasticene witness marks, to verify you have enough clearance between the valves and the piston top.
This is probably going to be very necessary regardless of what other engines/owners may report, since your engine would seem to have been modified in the past..
As Chris mentions, determining your compression ratio may be rather desirable/necessary too. Have fun !
Chris, thanks for the reply, my thoughts were along the same line, 2mm is not a huge amount, looks like the 2mm base gasket allows the piston to be at the correct position i.e.. level with the top of the barrel (if that is the correct position at T.D.C.)
Rohan, Thanks for the excellent tip re the plasticine, I was going to turn the engine over a few times once assembled, did not think about your suggestion. I will do this with a combination of all the gaskets and the the new composite head gasket.
Once the problem has been resolved I will update the thread.
Hopefully someone out there will remember the Piston position at T.D.C.
I faced this exact problem when fitting a new Hitchcocks sourced piston to my J2. The piston stood proud of the bore by 3mm at TDC.
My barrel had been shortened by 3mm at the base to fit the old Australian made aftermarket piston with a shorter deck height but of course I didn't think to check that before reboring and painting the cylinder.... I guess its what you had to do in the absence of parts or money back in the day.
The solution was to make a compression plate out of 3mm aluminium
then reassemble the engine with plasticine in the valve cutouts of the piston and rotate the engine. There were no marks from the valves in the plasticine at all so the clearance must be substantial in these old engines.
When reassembled it looked fine with the plate in place and runs well.
I suggest in the absence of any info to the contrary you aim for the top of the skirt to be level with the top of the bore at TDC then check clearance as described. No harm in checking the compression but in my case its pretty low for modern fuels anyway (6.25:1 according to the piston info) so has never been an issue.
ChrisX, Thanks for the information and images, looks like the barrel on my bike has been shorted as my piston sits 2mm above the top of the barrel and level with the 2mm aluminium gasket in place. I will carry out the plasticine test once I get the head back from the engine workshop, installing just the barrel gasket and composite head gasket (leaving out the 2mm copper head gasket from the 1957 clipper) My cyl. head is aluminium, not sure why the previous owner had installed the copper ring gasket as this highers the head by a further 2.mm. the but will find out once I get the head back. From your pictures, looks like your cyl head is cast iron, if so, is the cylinder head gasket just the copper ring sitting in the recess of the cylinder.head?
Chris, my head is aluminium so do not know at this stage why it has the cast iron type head gasket, I will check it all out when I receive the head parts from Hitchcocks and the workshop, who is fitting the valves, seats and guides. I will update the thread with the results and clearences once I have it sorted. Thanks to everyone for your inputs Stuart
Parts have arrived and took them to the engine workshop, sitting on the bench was a 500cc Bullet aluminium head, I measured the recess in the 500cc head, which was .205" compared to mine .165". does anyone know the depth of the recess on the 350 cc aluminium head? Thanks Stuart.