Possible bent valve stem causing engine to lock up

[George]

Hi,
Just some brief background info first. I have a 1972 S3 E Type V12 and I have just completed (save for the unavailable centre console) the installation of a conversion from auto to manual 5 speed using a Tremec T5 gearbox.
On completion I started the car and it ran for 2 minutes then came to a sudden stop there were no bangs, crashes or abnormal noises, it didn't slow down or stutter it just suddenly stopped. I tried to restart it but it only pulled in the starter motor without turning the engine, I bought a new battery and that also could not turn the engine over.
I tried to turn the engine via using a wrench on the end of the crankshaft but it will not move, I have now taken the new gearbox back out and checked that the new flywheel has no obstructions.
The engine ran well before I started the conversion and so I fear that I may have a bent/jammed valve clashing with the top of a piston therefore before I pursue removing the heads is there any checks I could do to prove it is a jammed valve or any other advise would be kindly welcomed.
Many thanks
George

[bitsobrits]

How long did the engine sit without running before you started it?

Does the engine turn with the gearbox removed?

Can you rotate the engine in reverse?

[George]

Hi Steve,

I ran the engine about 6 weeks prior to discovering this fault.
No the engine does not turn with the gearbox removed.
No the engine is jammed in both directions.
Thank you for your reply.

[christopher storey]

Oh dear ! First thing to do is to remove the cam covers and check for i.timing chains in place and correctly tensioned and ii. that each valve is where you would expect it to be .Since you cannot rotate the engine at present this will require some careful planning and a cool head to decide whether anything is out of place. If nothing obvious shows up, then the next thing is to remove each camshaft . If there is a bent valve then the likely outcome is that the relevant valve will not come fully upwards and will be obvious to see.

Marek is the expert on the V12 so it is worth emailing him ( PM's don't apparently work with him )

Good luck


PS I should also have said that removing all the spark plugs and examining what you can may help. A borescope would of course be invaluable

[George]

OK thank you Chris

[christopher storey]

George see my postcript

[George]

Hi Chris,
Yes I have a borescope and will take a look tomorrow down the plugs as well as inspecting inside the rocker covers.
Many thanks

[bitsobrits]

Hi Steve,

I ran the engine about 6 weeks prior to discovering this fault.
No the engine does not turn with the gearbox removed.
No the engine is jammed in both directions.
Thank you for your reply.

That is curious indeed. If it was a bent valve (and it would have to be very bent) you still should be able to rotate the engine in reverse for 270 degrees or so. A broken valve embedded in both head and piston could give your symptoms, but I still would imagine a bit of movement would be possible. My thoughts turn more towards a locked up oil pump or perhaps a spun bearing.

[George]

Hi Steve,
I have now had a borescope down each plug hole and can see nothing unusual but I cannot get the scope to look upwards at the valves.
I have removed the LH rocker cover and again can see nothing unusual. The reason for removing only the LH rocker is that I am getting a solid metallic thud from that area when I push the crank anti clockwise for about 1/2" and then sharply turn it clockwise for about 1/2" where it bumps something solid with a dull metal thud.
Tomorrow I will remove the cam shaft and see if I can tap each valve downwards.
The sound is not coming from the oil pump area.
Many thanks for your reply.
George

[Durango2k]

Maybe it sucked in some metal item like a nut ?

Carsten

[MarekH]

This is a bit bizarre as you report that you have done nothing to the engine.

The only new factor you have introduced here is how you change gear. Previously, this happened inside the gearbox automatically via solenoids controlled by hydraulic pressure and engine load. Now, you kick your foot on the clutch and the pressure is multiplied up to push a huge spring which sits inside the clutch cover bolted onto the back of the engine. This naturally pushes on the crank and presses it further forward.

So my question would be:- "Is there any freeplay pushing the crank forward and backward?" It should be only a few thou. I'd wonder whether you have a tight engine because all/some/one of the conrods are pushed up against each other because your thrust washer half way along the crank gives too much freeplay if the clutch is depressed.

Try pushing the crank pulley back into the engine (or prying the flywheel back towards the back of the car) and see whether you have more ability to turn the crank.

Don't whack metal against metal - it may identify where the problem manifests (as opposed to what the problem cause is) but it'll make a bad situation worse.

kind regards
Marek

[George]

Hi Marek,
Thank you for your suggestion. I have tried to move the crankshaft in and out and there is no movement either way.
The dull thud I get appears to be coming from the "A" bank nearest to the bulkhead.
Many thanks
George

[MarekH]

Without checking the manual, I'd have thought that the crankshaft should have up to about 3-4 thou freeplay forwards and back. Not moving at all is not the right answer.

(If you had kept your starter motor, then the new flywheel would have needed the same number of teeth as the old toque converter ring gear had.)

kind regards
Marek

[George]

Yes the auto ring gear and the new flywheel have matching teeth, I checked this when I removed the old one. When I started the car after the g/box installation it started fine with no unusual noises.
George

[mgcjag]

Hi George...just to clarity here...is the engine out of the car...gearbox separated from it....is the starter motor still fitted....is the starter pinion clear of the flywheel...thanks.. Steve

[George]

Hi Steve,
The engine is still in the car, the gearbox is out of the car, 2 of the bolts that hold the gearbox also hold the starter motor in place so whilst its not removed it is loose and clear of the ring gear.
George

[MarekH]

The valves were happily going up and down for a couple of minutes, so it didn't start with a stuck valve or a dropped valve seat. The valves should only be "down" when the camshaft lobe pushes them down and they should be fully "up" when the lobe is not pointing downward. When "up", the gap should be measurable and be the valve timing gap. Since you have access to the camshaft, you ought to be able to measure that. A valve, assuming it's not broken, that's not fully up for any reason should have a measurable excessive valve clearance when the cam lobe isn't engaged.

The pistons move up and down in complementary pairs adding up to 7. From the camshaft position, you should be able to work out which pairs are up and which pairs are down and which pairs are in the middle. That should give you a strong steer as to which cylinder is the problem if it is a valve problem.

You can verify adequate oil lubrication for the top end by loading some engine oil into a garden sprayer and pumping it into the oil pressure sender port at the back of the "V". You should see (and hear) the oil squirm its way out between the cam caps as it fills from back to front and then drain down the front timing cover.

That leaves the bottom end - which is where you made alterations. A likely scenario is that the crankshaft now sits a few thou further forward (because you have pumped the clutch and pushed it forward) and the old thrust washer had too much freeplay. The crank, conrods and crank bearing housings have all been pushed against each other a few thou and are now interfering with each other, rather than missing each other by a couple of thou.

So if the cylinder you think is the problem - numbers 5A or 6A by the firewall - has it's lobes pointing upwards and it's valve lash (timing) is good and there are no chunks of valve head sitting in the top of the cylinder, then you are probably looking at the bottom end seized up.

If you have a valve or valve seat problem, then obviously the head has to come off. If, as I suspect, it is a bottom end problem, then you can release and retighten all of the conrods/mains and make sure to check the thrust washer leaves you with no more than the permitted crank forward/backward movement/play. This would never have been an issue on an automatic because the crank is never pushed forward when changing gear, but the crank now likely sits a few thou further forward and everything that is hanging off of it is wedged together and interfering.

I sincerely hope it is this as it's an easy and cheap fix (gaskets plus new appropriately sized thrust washer) - no one likes taking cylinder heads off!

You also might need to rule out other causes - camshaft and crank got out of sync with each other, debris in chain maybe stopping you from turning crank... none of these are likely.

kind regards
Marek

[George]

Thanks for your help Marek, it will take me a while to check out your advise on the car and then I'll get back to you.
Many thanks
George

[George]

Hi Marek,
The valve clearances are between 10-12 thou. The rocker box is full of oil.
With reference to the thrust washer will this be visible by removing the sump or is it an engine out job?
George

[MarekH]

You only need to take the sump and baffle off. It's a semi-circular cresent bearing and it sits about half way down the crank. There are plenty of hits if you Google for it.

kind regards
Marek