Something tightening/siezing up when driving ???

[tractorjames]

Hello all, following my engine rebuild I am experiencing a very strange fault. It only occurs on a long journey where the speed is above about 60. Keep the speed down below 50 and I can drive around all day.

The issue is that when driving along, the engine/transmission suddenly starts to tighten up. (Feels like someone has pressed the brake pedal for you, hard as well) Upon feeling this, I dipped the clutch. As soon as I dipped the clutch the car will free wheel no problem but the engine stalls immediately.

Around the point of dipping the clutch there is a chaffing/grinding noise.

It has done this three times now, every time it does it I can get out of the car with my 15/16" spanner and turn the crankshaft perfectly smoothly and freely.

Get back in start it up and drive off. The engine runs sweet as a nut, no knocks rattles, pulls like a train, drives very well, the clutch is smooth, pedal feels nice etc.

The crank was reground mains and big ends, but thrust is standard, end float was tight - but within the specified range

The fact that the engine stops with the clutch pressed suggests to me that the issue is something forward of the clutch.

I've been pondering, clutch flywheels assembly or tightening up on the thrusts? The sound doesn't strike me as being an internal engine sound though, and it is quite loud, and a dry sound.

I think I am going to pull the gearbox out this weekend and have a look, but if anyone has and suggestions to fire about it would be interesting.

James

[tractorjames]

Ill just add that there is no prior warning, it happens all of a sudden and is all over in less than 5 seconds!!!

[milothedog]

No idea James, but if it was thrust washers then they would be trashed by now I would have thought and you would notice the idle drop when you dipped the clutch normally if they had too much end float.

A couple random ideas

I thought, maybe fuel starvation giving you engine braking maybe, but that doesn't explain the noise


Also, thinking outside the box. an exhaust silencer blocking up (something floating around inside it) but again doesn't account for the noise

[tractorjames]

Those were my thoughts RE thrust washers - there is no dip at all in engine revs when clutch is pressed, had the pry bar on the crank and by rack of eye there is a fee thou end float, nothing excessive it is just noticeable by eye.

The "braking effect" is very strong. It is comparable to hard braking, I mean harder than you would usually be braking on a leisurely cruise to work.

Thanks,
James

[milothedog]

Those were my thoughts RE thrust washers - there is no dip at all in engine revs when clutch is pressed, had the pry bar on the crank and by rack of eye there is a fee thou end float, nothing excessive it is just noticeable by eye.

The "braking effect" is very strong. It is comparable to hard braking, I mean harder than you would usually be braking on a leisurely cruise to work.

Thanks,
James

I think if it was anything to do with a crank bearing you would have known about it by now. If it got that tight it would have "picked up" a shell or two.

[davidf]

Really sounds like the engine has 'cut-out', but what about the noise?

Quote Around the point of dipping the clutch there is a chaffing/grinding noise.

Is this noise before you press the clutch, or while it is pressed?

[SGN]

Just a thought and might be completely off the mark, but is your viscous fan ok, mine gave the effect of engine braking as it howled , I have an auto and I as convinced the gearbox was the cause, horrible noise, might be worth a check.

Cheers
Steve

[michael]

Some one that worked for me had a similar problem one morning on his way to work. He rang me and told me his car kept feeling like it was braking on its own and struggling to accelerate I told him his brakes could be sticking on , so he popped into a local garage and they said they were sticking so he booked it in with him. When he arrived at work I looked at the brakes and they seemed ok . So we went through the symptoms of self braking ect . I then checked his oil level it had hardly any oil in it and was partially seizing up . Put oil in it problem solved . I doubt very much that this is your problem as stag owners check check and check again. But you did mention an engine rebuild and something could be blocking the sump pick up at high revs when the pump is pulling harder . Probably I'm talking rubbish but you never know.
Hope you find it soon . Michael.

[Paul Goldsmith]

Oh yes Steve, if my own hideous noise is disappeared by replacing my failed VC I'll be so happy.

Otherwise it does sound like a terminal engine or gearbox failure !!

[tractorjames]

There is fair panic strikes when it occurs so it is hard to give a perfect sequence of events. I hate to think it but my mind is somehow swaying towards a piston nipping up

[tractorjames]

Viscous is OK

Thanks for all the thoughts.

JAmes

[milothedog]

There is fair panic strikes when it occurs so it is hard to give a perfect sequence of events. I hate to think it but my mind is somehow swaying towards a piston nipping up

Again James, I can't see it and for your sake hope to be proved right. Especially as you say it all turns freely immediately afterwards, starts again afterwards and runs perfectly.

Anything getting that tight in an engine (enough to stall it at speed) is going to cause serious damage to bores, pistons, bearings and journals (whatever is loosing its tolerance for whatever reason)


Fingers crossed for you

Ian.

[Paul Goldsmith]

Oh yes Steve, if my own hideous noise is disappeared by replacing my failed VC I'll be so happy.

Otherwise it does sound like a terminal engine or gearbox failure !!

Sorry James, I hope my badly worded response to Steve didn't alarm you. Upon re-reading I meant the failed VC noise sounds like a more terminal issue, not meaning your own situation is.

Fingers crossed you get it sorted soon

[SGN]

Sorry James, I hope my badly worded response to Steve didn't alarm you. Upon re-reading I meant the failed VC noise sounds like a more terminal issue, not meaning your own situation is.

Fingers crossed you get it sorted soon

Hi Paul, I missed your post about the VC, only just read it,
Part of the reason I posted about the VC was, that in the past when I've had a problem after work has been done, it's all to easy to get clouded judgment and convince yourself you did something wrong, when it's possible it's something totally unrelated. (Been there, got the T shirt )

Good luck James, hope you sort it soon
Cheers
Steve

[flying farmer]

As it runs ok up to 50mph and the problem occurs at higher speeds I would suspect it is a heat related problem. It is possible the piston to bore clearance is a bit tight.
My theory is that once past a certain point, the piston skirts get progressively tighter in the bore, even more heat is generated through friction so the pistons expand even more to the point where the oil film breaks down and the pistons begin to seize in the bore.

Having stopped the engine the heat will rapidly transfer to the block and the pistons will free themselves.

This reminds me of a problem with Triumph straight six (2.5) pistons sometime in the 1990s. A concours rebuild was heading to the national day on its first significant run out, on the motorway, and it seized on the way to the show.

Some months later I was rebuilding my 2.5PI saloon engine with a rebore and new pistons and I had reason to contact Chris Witor for some parts. I mentioned the rebuild to him, and he said " make sure you have the bores honed half a thou oversize as there has been a lot of seizures with a particular batch of pistons"

His theory was that the grade of alloy in the pistons was different from the original and were expanding more causing the problems.

Unfortunately for me I had already got the engine installed in the car, so decided my best option was to run it in VERY carefully and keep off the motorways for a the first thousand miles. I had no problems with it despite thrashing it mercilessly after a prolonged running in period, but as it was my daily driver and I was averaging 12,000 miles per year, the first thousand miles didn't take long to achieve.

Am I right in thinking you used a set of the JP high compression pistons? They may be a different grade of alloy compared to the County or original pistons.

When I rebuilt the engine on my 1st Stag I found it was fitted with JP pistons (county ring set doesn't fit). The number 8 piston was significantly scuffed on its skirt, though the damage was more visible than it was measureable. I assumed it was a result of an overheating episode caused by head gasket failure as I had receipts in the history file for 3 sets of head gaskets within 15'000 miles (block needed skimming), but maybe the problem was more akin to what you are suffering.

I very much doubt that it is a crank problem in your case as anything that created that much drag would wreck the bearings, and as the crank is cooled by the oil regardless of the loading, it would not in my opinion, free itself off again, and if it did you would notice a change in oil pressure.

I agree that the VC can make engine seizing noises, I have heard them myself when asked to diagnose a problem on someone else's car, though a wobble of the fan blades proved the VC was shot in that instance.

I think if it was my car I would treat it very carefully for a while, no more than 50mph, then after maybe 500 miles try it to 60. Short bursts of hard acceleration should not hurt it, but then back off and let it cool. Make sure your ignition timing is correct and the mixture is not too lean as this will generate significantly more heat.

My project Stags engine sounded like a bag of nails when I first started it, lots of valve train clatter, which is why I am running it in extra carefully. I have now done about 400 miles and it is pretty well silent.

Neil