Bottom end timing

31st August 2011, 23:17

Right heres a quick question - might sound daft to some I know but hear me out as I'm thoroughly confused by what this engine is doing:

Should my pistons be in this position when the little hole (for TDC i think it is?) is something in it - going through the flywheel. Pics might explain better than I can. I seem to have had light piston/valve contact so whipped the head off to have a look.
I timed it with the bottom end at the setting in the first picture (allen key in hole on block) and the head in the safe position, so the hole is viewable through the cam pulley opening. Could it be that Ive got the flywheel on incorrectly so its showing the "TDC hole", as I shall call it, when the crank is in the wrong position?
All the valve clearances are as the book states - 0.20mm on the inlet, 0.40mm on exhaust. The headgasket was an FAI one for a 1.6 xsi engine which is what this is.

31st August 2011, 23:58

Cylinders 1 and 4 are at TDC, so the bottom end has been locked off properly. Looks fine to me.

Could be the head was skimmed and the head gasket was a little on the thin side, hence some piston and valve contact?

1st September 2011, 00:07

This is it you see, if that were the case then it wouldnt have worked at all - I timed it up yesterday evening right on the money, turned over by hand perfectly. Came to start it today, a few turns then "clunk". Checked the timing belt and it had gone floppy down the front by the alternator, a sure sign the tensioner had moved. By this point i'm thinking "bent valves" so I timed it up again but it just wouldn't turn over by hand, was locked solid and you could hear a metallic thunk in the engine as if valves were touching pistons. So I pulled it all apart just, very slight marks on the piston crowns and on the valves but none are bent as they all look fine and hold back petrol when poured in the combustion chamber so they are sealing.
Thats what got me thinking has the timing moved slightly when the belt went floppy but then that wouldn't explain why it wouldn't turn when I redid the timing once more, and thus me whipping the head off to check the valves. To say i'm very confused is an understatement

1st September 2011, 00:13

Sounds odd. So you turned the engine over by hand a good few times, and checked belt tension again before starting?

Doesn't sound like it's caused much damage, so chances are when you stick it back together it'll be fine.

1st September 2011, 00:19

Yeah I turned it over a good 5 times or so, as I wanted to get it right and make sure the belt was running true. Got a 90 degree deflection on the timing belt down the front run up to the cam pulley as it should be - I bent a valve on a metro gti years ago changing a timing belt so I didnt want a repeat of that scenario!
So its now its another new gasket and bolts even though the old ones are only 4 days old and havent been run.
One thing I did notice was that Number 2 bore was half full of coolant again, as thats where the gasket went last time) but I think that might have been were I pulled the head off and lifted it up and it ran in?

1st September 2011, 00:25

Another thing to say is the engine was turned over yesterday dry, today it had coolant in - could it be the water pump is forcing water into the bore somehow, say its cracked or something? However the machine shop didnt pick up on this nor can I see any cracks in the head would allow water into the bore
I just went to check the inlet manifold and number 1 port of it was full of coolant? now how would that happen?

1st September 2011, 09:42

Must be the headgasket or a crack in the block if its leaking in from the waterjackets, if the cylinders were filling up with coolant that fast then be careful not to hydro-lock your engine, if your cylinders are filling with coolant then there is a possibility that it could get into the inlet port, have you just fitted a new head gasket then?

1st September 2011, 10:17

Ive checked for cracks and cant see anything visible. What i've done is turn the head upside down on the work bench and then fill its water jackets with water - so tonight I'll check to see if any has leaked away. Couldnt see any marks/cracks in the bore too but what i'm going to do is put the old MLS gasket on as its never been run, do the head up but not torque it right down and put water in and then turn it over by hand. Obviously this wont give me the fire ring sealing of a proper head gasket job, but should seal the water and oil ways enough to check that for leaks into the bore once I pressurize the system.