Hitchcocks Forum

Can anybody please confirm that the inlet valve on a 350cc Indian built is larger in diameter than the exhaust.

Well, my 2008 350 has a larger inlet.

Hi ROB ---- are the sizes given in the "Tech. data" section of the manual ?? OR }---- phone our hosts ( they've been weaned OFF canabalism now !!)----they'll know.

Inlet valves are always bigger than exhaust except in certain modern (which enfields most certainly are not) engines where there may be 2 inlet valves.......Has someone perchance disassembled a cylinder head without labelled what came from where??????

As bb says, inlet valves are always larger, even if there are multiples, e.g. if you have an odd no per head the extra one is always an inlet, so 3 per cyl, =2 in 1 ex, 5 = 3 in 2 ex.
The simple reason behind this is, it's harder to stuff the gases in than it is to push them out, think toothpaste tube, imagine how hard pushing toothpaste into the tube is compared to squeezing it out.
I've never yet seen an engine where the valves are the same size in/ex.
So short answer, yes, inlet = larger

Fitting them to the head will show up which goes where pdq.

Some inlet and exhaust valves are equal sized, like in earlier Truimph Tiger Cubs, for example, but the 350 Bullet inlet valve is a little larger than the exhaust valve.

Paul.

Thanks to everyone for the replies. No I did lable but had to make sure as I had it rebored and fited a new +20thou piston and rings, but it will not start. The carb was found to be blocked now that is OK. Compression is not what I would expect, able to turn engine over by hand using thd kick start. Trying to eliminate all possiable reasons for not staring. Timing has been checked and is correct.

"Inlet valves are always bigger than exhaust valves"...WRONG...many engines have same size valves...I have a Norton Dominator with equal size valves.

Rob. An engine will not start if it has no compression. You will have to check everything as far as valve shutting and sealing goes. I am assuming you have not broken all your piston rings when fitting the barrel (see later). Most obvious is the tappet clearances, check those first. Then pour a little engine oil in the plug hole (refit plug) and see if compression feels better. If better something is wrong with the piston rings. If not, the valves are leaking...most likely is the exhaust valve has stuck open slightly with carbon build up on the valve stem. Remove exhaust pipe and get someone to help kick over the engine. Either listen for leaks at the exhaust port or use a small amount of soapy water around the back of the valve and look for bubbles being blown. Do the same for the inlet. If any or both valves are leaking the head will need to be removed for valve cleaning and grinding. Another possibility is the decompressor is not sealing.