12 replies to this topic

[lotusk]

Hi all,

I had, what seemed to be, a valve seize on Friday evening and have now taken the head off. On inspection the valve seems fine but there is some very light scoring on the top of no2 piston.

Can anyone confirm whether this will be ok to continue using? Or will I need to replace the piston? It is very light... hopefully the photos show.

Thanks,

Kieran

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[adcyork]

That looks like marks left from someone using a hard wire brush to clean the piston crown. You'd expect it to be like that on the other three if that was the case though...

Was it that cylinder that the valve stuck on?

[wile e coyote]

Fine to reuse - if source of scratches is unknown check your bores closely for damage, but 2& 3 look suspiciously clean whilst 1 & 4 carboned up nicely so I'd suspect as above some overenthuasiastic cleaning has gone on...

[lotusk]

The centre branch of the manifold was glowing red hot and I could hear knocking from the head - that's why I suspected a seized valve.

The valves on no.2 look fine but there is a lot of carbon deposits near the exhaust valve. I suspect 2 and 3 were running very lean, hence the glowing manifold and clean pistons.

Hmmmm... Not sure what's happened really.

[lotusk]

Just had a closer look at my cylinders - They look fine to the eye but when I ran my finger around the surface of the bore I could feel some light scoring. I presume this means they have had it??!

This was on no 4 and 2 cylinders.

[bmcecosse]

Maybe something has passed through the engine ? But glowing red centre manifold suggests vry weak mixture - possibly there was detonation going on due to the extreme heat ? What state the spark plugs ?

[lotusk]

The plugs are very black, as though it was running very rich! Thats what is really confusing me!!

I guess it could have been oil getting past the rings, or down through the valve guides though...

Am I correct in thinking that even slight scoring on the bores means the rings will never seal correctly?

[mike.]

If it was running hot and was knocking, as above, sounds like detonation. Detonation can cause serious piston damage....

[lotusk]

Yep, and I had problems with it pinking low down even before this happened.

Any thoughts on the condition of the bores?

[bmcecosse]

Well - pinking leads on to detonation ! Slight scoring - as in cross hatch honing - is good! But anything deeper than the slightest mark is not good. However - if you don't want to pull the engine and inspect the pistons - you may as well run it!

[lotusk]

It is definitely more than just the cross hatch from honing. I'll pull the engine and take it all to bits... don't want to put it all back together and have the same happen again.

Plus I get the impression that whoever built it didn't really do it very well - no thermostat or restrictor in the housing for example!!!

[bmcecosse]

Hmm - well that may have been done to disguise a serious overheating issue!

[lotusk]

That MED block starts to look even more appealing - I'll go and start planning which body parts to sell!!