Chim Snapped valve???

[L1 UUD]

Hi

After rebuilding my 4.0hc motor last week, with skimmed second hand heads, do to mine failing, the car sat running for a good couple of hours to check for temps and leaks etc.

Then bang !! Under investigation its snapped a valve !

My engine builder says he's never seen this happen,

Has anyone else seen or heard of a snapped valve in the rover V8 ?

Any thoughts greatly appreciated..

[keynsham]

Never and I am not sure how a valve 'snaps'? Was it the stem that snapped? Any pictures?

[L1 UUD]

No pics yet, going to have a look this afternoon.

Yes valve stem snapped clean.

[Belle427]

Valve to piston contact possibly.

[TarquinMX5]

New valves or 'as-fitted' in secondhand head? To answer the question, not heard if it before.

[keynsham]

Interesting! Valves should have no bending loads really in the stem, just compression and a little tension. If the piston hit the valve becasue the valve dropped into the cylinder I suppose it could break off at the stem. Difficult to imagine though! I look forward to some more piccys and info when you have some. It is certainly and interestng but very unwelcome occurance!!

[L1 UUD]

Hi, popped over to the workshop.. here's the damage.

[L1 UUD]

[L1 UUD]

Valve snapped at the top, clean through, luckily jammed and not destroyed anything bit the valve guide, piston coming out for a check over.

Cheers.

[Boosted LS1]

Could be fatigue, stress fracture, coil bind or contact with the guide. Worth having a close look at the others whilst in situ.

[Sir Paolo]

Agreed, everything needs a thorough check over.

And as already mentioned, I thought of valve to piston contact.

I note you state that the heads were second hand(?).
It’s possible that they’ve already been skimmed to limits to correct warping or to raise compression(?).
Of course, an HC has piston cut-outs to reduce this eventuality as built.

With this in mind, did your engine builder do a trial build with oiled plasticene on the piston crowns, then turn the engine over by hand only?

It’s a bit of a phaff, but I have done this, and sometimes it’s the only way to confirm clearance.
It’s cheaper in the long run.

[QBee]

Did you change the camshaft during the rebuild, and if so, to what camshaft?

[Steve_D]

I'm confused.
You have said more than once the head snapped of but the photos are a bent valve not snapped.
If the bent valve is what you have then were the valve springs still in place? If they were not then the fail was a 'Dropped Valve' where the collets had come adrift allowing the valve to drop down and be collected by the piston.

Steve

EDIT. Sorry just re-read the post so the stem snapped at the collet groove? If those were new valves then a manufacturing defect.

Edited by Steve_D on Saturday 30th July 00:05

[L1 UUD]

Hi
The valve has snapped at the top, clean sheer through. We assume that is has then dropped through the guide and hit the piston, bending the valve and jamming back into the valve port. Once the head was removed then the valve could be pulled through. Luckily only just marking the piston.

[L1 UUD]

Not great resolution but hopefully you can see the sheered head of the valve.

Cheers

[Steve_D]

Not seen it on a RV8 but have on another engine. Also seen where the collets have progressively worn the groove they lock in until they have finally let go allowing the valve to drop as yours has but again not on an RV8..

Steve