The V8 Owners Forum -

ChrisJC wrote:
I think a compression test will read very low if the valve timing is miles out too.

Chris.

......and the valves may well now be bent.

ChrisJC wrote:Hmm, that's interesting. How far from TDC is No. 1 (or No. 6 for that matter, it is the same as No. 1) when the valves on no. 6 are 'on the rock', i.e. both equally open?
I don't know that it has to be perfectly at TDC, but in the ballpark is a must.

If it's 1/2 way down the bore, then that is your problem.

I think a compression test will read very low if the valve timing is miles out too.

Chris.

Hi Chris,

No1 seemed to be between about 1/4 down the bore.so yes you reckon that's where the prob may lie... Not quite sure where I go from here?

Unless you have faulty parts like cam and wheels, it's near impossible to get the timing out. Assuming you lined the dots up. And has been said, a couple of teeth out or more will result in valves hitting the pistons.

I did have an aftermarket cam and components where the dots wouldn't line up perfectly. Exactly between teeth. If they can't get a simple thing like that right, makes you wonder how they could grind a cam accurately.

DaveEFI wrote:Unless you have faulty parts like cam and wheels, it's near impossible to get the timing out. Assuming you lined the dots up. And has been said, a couple of teeth out or more will result in valves hitting the pistons.

I did have an aftermarket cam and components where the dots wouldn't line up perfectly. Exactly between teeth. If they can't get a simple thing like that right, makes you wonder how they could grind a cam accurately.

New cam,cam wheel and new timing chain all from rimmer bros. I took a great deal of time ensuring that the dots did line up, but the oringinal did have a much clearer,simpler dot than the aftermarket wheel. but now doubt has set in.....

On a rebuild, the lifters may not have pumped up fully yet, so judging TDC by valve movement may not give accurate result.

Hopefully you have a timing mark on the front pulley. If so use this to find TDC. Then no1 and no6 will be at tdc when the mark is lined up.

To find which is on the firing stroke then look at the valves. If there is any valve lift at all at no6, then it's firing at no1 and both valves at no 1 should be shut.

In the distributor, one of the high points on the reluctor should now be next to the pickup. If not rotate the dizzy till it is. Rotor should now be pointing at the lead going to cylinder no1. If not reposition all the leads or remove the dizzy and reposition the shaft so that the rotor is pointing at the lead that goes to no1.

This should get you going and allow you to set thing properly with a timing light when it is running.l

R0vers wrote:

ChrisJC wrote:Hmm, that's interesting. How far from TDC is No. 1 (or No. 6 for that matter, it is the same as No. 1) when the valves on no. 6 are 'on the rock', i.e. both equally open?
I don't know that it has to be perfectly at TDC, but in the ballpark is a must.

If it's 1/2 way down the bore, then that is your problem.

I think a compression test will read very low if the valve timing is miles out too.

Chris.

Hi Chris,

No1 seemed to be between about 1/4 down the bore.so yes you reckon that's where the prob may lie... Not quite sure where I go from here?

For me, that would trigger me to explore this further.
I would try to understand if the timing marks on the crankshaft pulley agree with where No. 1 piston actually is.
I would also remove the inlet manifold so I could see the camshaft and followers and try to convince myself that the valve timing was as I expect. Doing this only costs some rocker cover gaskets and a valley gasket and is pretty trivial, unlike taking heads off (or timing cover / sump off!)
I would verify that when the camshaft thinks No. 1 is at TDC (i.e. both valves on No. 6 are equally open), then the distributor (both low tension and high tension parts) is about to fire on No. 1.

Chris.

Well I've certainly got lots of routes to explore. thanks for all of your comments and helpful suggestions. I will take a look on Saturday and report back to you - hopefully with some positive news!!

I'm wondering if the fact it is a re-built engine with honed bores and new rings which hasn't been run at all and stood for while has a bearing? IMHO, that won't get full compression until the rings bed in?

Many years ago I did a similar thing to an MGB engine and took it from London to Aberdeen to fit it. And it simply wouldn't start. Checked all the usual things several times. We had to move the car to another storage place, and while it was on tow, I tried a bump start. And it started near instantly.

DaveEFI wrote:I'm wondering if the fact it is a re-built engine with honed bores and new rings which hasn't been run at all and stood for while has a bearing? IMHO, that won't get full compression until the rings bed in?

Many years ago I did a similar thing to an MGB engine and took it from London to Aberdeen to fit it. And it simply wouldn't start. Checked all the usual things several times. We had to move the car to another storage place, and while it was on tow, I tried a bump start. And it started near instantly.

bit of a chicken and egg situation - the only trick i know is some oil down the bores - but are there any other ways to up the compression to initially get it going?

You may have already looked at it by now but what I do if a vehicle comes in as a non starter is firstly check for spark,which you have,then spin it over and squirt "easy start" down the carbs to see if it fires up.The "easy start" will show you if the carbs/fuel system are at fault or not.
If all this fails then a compression check then,in your case, a valve timing check.
Let us know how its progressing.

UPDATE! (Don't get too excited)

Dave EFI of this parish, very kindly popped over on Saturday and we went over all the checks that I had. We systematically went through all the basics:

Spark - Checked and white spark - but seemed to be dancing around the electrodes a little.

Timing - Was out by around 20 degrees and with the use of a strobe on the starter, we managed to bring it back in-line with where it should be.

Fuel - checked and all seemed to be fine at carb end.

Starter - Spinning too easily - almost as though there is no compression.no change in the 'note' either.

Compression Test - 0-10 PSI at the best on most of the cylinders!!!! Even on a knackered engine it should be around 100!! We investigated a little further. This would explain why it would not start!?!

We filled the bores with quite alot of oil to see if the new pitons and rings had any issues, but again, still very compression (no change from previous readings). After much head scratching we thought the problem must be the inlet/exhaust valves not seating properly. When I rebuilt the engine(and cylinder heads) i didn't grind or lap in the new seats,as i though they looked spot on!!

VALVES AND SEATS.

I stripped down the heads and did a leak test on both cylinder heads. I Popped the heads on their sides and filled the ports up with paraffin. Within 5 minutes, all the seats were seeping fluid (about half a teaspoon full) - meaning the new valves weren't seating in the head properly!! Checked the other head and found the same issue..........

So this morning i've just dropped off the heads at a local engine shop, who are re-cutting all 16 seats and lapping them in for the new valves. Whilst the heads are there, and for peace of mind, ive also asked them to change the valves guides with new ones which i has a part of the head rebuild kit (and i didn't have the kit to do those at the time)

So.... I'm hopefully picking up the "new" heads on Friday and can see if the engine actually starts now!!!
A huge thanks to DAVE EFI - for all of his help and knowledge !!

Pleased to be of at least some help.

Just to add, was very impressed with the workmanship of your engine re-build and installation.

Keep us informed of progress. Once it's running, the carbs will likely need a tune.

One point which has caught me out is that the machine shop MUST cut all the valve seats to the same height. Otherwise you will never be able to get the valve preload the same on all the cylinders.

Chris.

I would not expect that amount of valve leakage to prevent the engine from starting. I would have still expected some half decent compression with only that amount of paraffin leaking after that time . You would have found that after an hour or so running the valves would have hammered themselves into the seats and sealed them.

Are you also taking the front cover off whilst at this level of tear down to re-check the timing?

On an engine with perhaps a couple of burnt valves and poor compression on those cylinders only, you might well get it started quite easily. But with near zero on all cylinders? To explain further, it whizzed round on the starter as if the plugs were out.

Might have started with a tow, though.

Certainly with some soft cast iron seats, opening up the tappet clearance could sometimes result in the valve sealing again. Something often done on the old Rover IOE engines. But would it work with hardened seats?