Forum

[stuart_g]

I am doing a rebuild of a Mk1A Interceptor engine and think I may have the cam timing wrong??
I have set the crankshaft pointer so it is pointing downwards and have the marks on the cam sprockets facing each other as best as they can, they are both slightly pointing upwards when they face the centre of the engine.
The problem is that when I turn the engine over there is a point at which both valves are open, one valve hasn't finished closing before the other opens and therefore they are both open at the same time, this results in you being able to look down the inlet and see through the engine and out of the exhaust port. This doesn't look right to me as I thought one valve had to be closed before another would open??

Anyone got any suggestions on what is wrong here or is this correct?

Thanks

[Mark M]

Stuart, something is clearly wrong. You have the timing marks correct, the two cam sprockets never exactly line up so that's ok. Unfortunately over the years Enfield produced several different inlet and exhaust cams and several inlet sprockets. These can be mixed and matched quite a bit, sometimes this was done deliberately by the Factory to produce different engine characteristics. I have a late Mk1, very similar to the 1A and am currently working on a Mk2 as well as a Connie and a Meteor. Where are you? I'm near Silverstone (Northampton will do!) and might be able to help. Finally there is a Yahoo News Group especially for Inters, come and join us at https://groups.yahoo.com/neo/groups/RE_Interceptor/info where there is lots of help and info. There are a good few of us in the UK, (most Inter Owners are in the US and Canada) we hold a Rally in July near the Factory in Bradford on Avon which is always good, come along, even if the bike is not ready!
REgards, Mark

[Mark M]

You can email me at mumforduk(AT)hotmail(dot)com, fill in the brackets to complete address.
REgards, Mark

[Bullet Whisperer]

Stuart, it might be ok - if you have both valves shut at TDC compression, but on the next TDC, they are slightly open, this will be quite normal as long as the inlet valve is just starting to open and the exhaust valve is closing. The valves might have 2-3 mm of lift on them going over TDC on the 'overlap', but as long as they are not fouling the piston crown or each other, your valve timing could well be correct. If the valves are open by a very large amount, ie half way open or more, then something is probably wrong with the timing. Regards, Paul.

[stuart_g]

Thanks for the replies.

I have had another closer look and the problem is occurring after the exhaust valve has been fully opened and is on it's way to close, when it is nearly closed the inlet valve starts to open. On the next revolution both valves are closed.

Nothing hits anything it turns over lovely and has lots of compression.

Bullet Whisperer - Is this normal then as to what you were describing?

[Colin F]

Stuart,what you're describing is valve overlap.You could always set up a degree wheel
on the crank and work out if the Cam timming is within specs.They should be listed in the manual.
colin

[Barnes]

Hi stuart, i rebuilt a freinds inter 1a last year and you are describing the exact same thing as i found. the bike still runs nicely and most engines have a degree of valve overlap built into them. the interceptors to appear to have abit more as my super meteor is no where near as much. ed

[Bullet Whisperer]

Hi Stuart, what you are describing is what I explained. As long as the exhaust valve is well on its' way to closing and the inlet valve is just starting to open at the 'other' TDC, you should be good to go seeing as you say it turns over nicely and has compression. For example only, your valve timing might differ slightly - the inlet valve can start to open, say, 45 degrees BEFOPRE TDC. At this point, the exhaust valve will still be open and may not close fully until, say, 45 degrees AFTER TDC. This means that AT TDC, both valves will be partially open and the vast majority of four stroke engines will display this tendancy, it is quite normal. Regards, Paul.

[stuart_g]

Thanks very much for the replies everyone. It has put my mind at rest.
I am rebuilding this for a friend so I need to make sure I get it right first time.
I have no prior knowledge of these engines, this is the first one I've rebuilt.
I have got experience with modern Jap 4 cylinder engines but nothing as old as this.
Thanks again.