Engine assembly questions.

[jansens]

What is the thickness of the silicone gaskets people are using? Mine seems to be about 0.8mm.

The instructions from Paul that came with the cam say "Set the cam equal over TDC. Advancing the cam gives more bottom end retard means more top end should you need to change from this setting". I am not sure exactly what that means though.

A degree wheel would be nice but I don't have one so I improvised. I put tape on the flywheel and set up a fine wire pointer on top of the crank case. I then used a DTI on the crank to measure TDC and make a mark on the tape against my pointer. I then did the same with the DTI on the inlet and exhaust valves. Nothing was done hugely accurately but I did it multiple times to make sure the results were at least vaguely consistent.

As it is currently set (with the marks on the gears matching as it happens) the point at which the inlet is just starting to open and the exhaust just finished closing are about equal around TDC. Moving the cam gear to tooth forward or backwards would make it definitely less equally spaced. I'd have to move it around 2 teeth to get the cam opening right on TDC.

Given I am limited by how much I can adjust things anyway I think this is as good as I can make it now.

Simon

[Bob Culver]

Ardent followers of the Forum should note that the camshaft referred to is not the standard pattern. For those the inlet opens tdc and the exh closes 15 deg after tdc, so the valves are equally open at 7.5 deg atdc. A manual for another make gives tolerance as +/- 3 deg. (Determining valve timing directly  from  positon at apparent full lift is not accurate.)

[jansens]

I've now attached the rods and pistons and did a test assemble (no piston rings) but with the base gasket in place and bolted down tight but not with all the nuts in place. I measured the pistons as being 9 thou under the top of the block at TDC. For an engine that you want to rev I seem to remember 20 thou below the block being the safe value? I thought it says in the companion but can't find the page and even though Ian has told me many times before I can't remember the exact amount!

I am using a home made silicone block base gasket and the thickness of that is 0.8mm. Our spares Guru measured one of the ones the local club sells and told me they are about 1.2mm thick. It seems to me I should get one of those and remeasure to see if it gives me the extra clearance I need. I guess the amount of clearance will shrink a little once that's done up really tight and settled.

Rather stupidly I had everything balanced before doing all this so now if I do need to machine anything off the middle two pistons I will need to very carefully make sure the outer two still match in weight.

Once I have the block/pistons sorted I want to check the cam timing again as I can then find TDC much more easily with the pistons in place.

Simon