Stuck valve?

[barnfind]

After my last bodywork foray, I decided to have a quick check to make sure that the engine was free. Since I haven't yet plugged all the wiring together I decided to do it by taking the plugs out and rolling the car along in 4th gear. This would also have the effect of pushing out the surplus Redex squirted in a few weeks ago.The engine had rotated freely last April when last tried and so I did not really anticipate any trouble.

Upon my first push, the car rolled a foot or so, the fan rotated happily and then, everything came to a halt. I rolled it back and after a similar length of travel, same result. I slipped her out of gear and repeated the push, but everything ran free, so nothing to do with the transmission.
Rather than do something hasty and doing some damage (and running out of daylight) I retired to consider what might be the problem.

The effect is like that of a piston encountering an obstacle at TDC and I wonder if one of the valves is stuck open, and if so, is this an 'interference' type engine where piston and valves can clash if the timing chain is removed or breaks. I have read that this engine naturally comes to rest with one exhaust valve open. Perhaps this has finally stuck in place after 16 years in a barn.

I haven't removed the rocker cover to see what is happening in there, and perhaps that should be my next step, but peering down the filler, suggests a clean, well oiled engine, without rust or sludge in evidence.My other thought was that the starter had jammed in mesh, but that would not explain how it would revolve so far and then stick.

Can anyone advise whether valves and pistons can clash in an 845cc. If not, has anyone any ideas or experiences of this sort of thing. The engine mains, big ends bearings and pistons are clearly not seized.

 

[politeperson]

Sticking engine

Happened to me many years ago.

Turned out to be interference between the pulley of the end of the cam shaft (water pump) and the engine. Took some finding.

Why don't you turn the engine with the car in neutral to isolate a gearbox/ drive train fault?

You can turn the engine with a 17mm socket on the cam shaft pulley gently to see (or feel )what is going on.

Have you dropped something down the plug hole? telescopic magnet?

Luckily removing the head is a small job on one of these.

Good luck.

 

[barnfind]

Thanks for that. The car is free rolling with the gears in neutral, so unless it is clutch related, that more or less exonerates the diff and most of the gearbox. I probably also need to reconnect the clutch cable and see if dipping the clutch makes any difference.
However, if the transmission was jammed in some way, then I wonder if I would still get that initial free movement up until the point at which it locks up.

 

[alewis]

Its worth a look under the rocker cover as its quite easy and will make any problems visible.

I had a similar problem with an old generator (coventry climax overhead camshaft job) - took the head off just to find crud on top of the cylinders causing the problem!

 

[benchseat]

To answer the initial question - pistons don't collide with valves in an 845cc if the timimg chain breaks. You simply glide to a halt!

 

[barnfind]

It is a puzzle and the fact that it goes so far before jamming, (in either direction of rotation) suggests some kind of interference, even though the view has been expressed that this isn't usually the case on an R4 engine.

The stop is so abrupt, I can't think that it is a pulley binding as suggested by politeperson.

Starter motor? I shall have to get my spanners out when next I get some time.

 

[politeperson]

The webbing on the back of the pulley casting was catching on a protruding stud from the block I remember, causing a sudden stop. I agree it is pretty unlikely in your situation, I had been messing around swapping engines.

 

[barnfind]

I have posted on my project thread what happened in the end, but for completeness, I will repeat it here (there's nothing more frustrating than a thread with no outcome when you have done a search for the topic).
After several months thinking whilst doing other work on the car, I decided that the cause was probably a valve jammed shut rather than open, thus allowing only a small range of movement when the follower was on the back of the cam.
Over several weeks I sprayed the valve gear, first with Plus Gas, and then with WD 40, and eventually jacked up the offside wheel, took out the plugs, chocked everything else and without much hope really, turned the wheel with the car in 4th gear. Much to my (pleased) surprise the wheel rotated showly, accompanied by fan, valve gear etc. I revolved the wheel several times to make sure everything was loose, and cheered (quietly).