VVC Head

[Paul-R]

I recently removed a VVC head for inspection (that had suffered a HGF/overheating) and found that the liners have made grooves (>0.25mm) in the head (I assume from the heat generated). Other than the grooves the head still seems relatively flat with distortion of <0.05mm, which I think is acceptable. The rubber from the head gasket had also stuck to the head.

 

Has anyone had experience of this and are heads such as these generally recoverable with a skim or is the head now likely to be 'soft' and lead to a re-occuring HGF if re-used.

 

Paul

 

[Peter Carmichael]

The head is likely to be soft, but this is worth checking. 0.25mm is 10thou. I have had heads recovered from 20thou skims, but you need to reshape the combustion chamber to reclaim volume and keep the compression ratio sensible. Should be possible, but a bare head can be had for pretty reasonable money so it may be worth looking out for a good one.

[Bob Corb]

If it hasn't gone soft then I would have if skimmed by 0.3mm,although you should measure the compression ratio first. Most K 1.8's are about 10.35:1. The top limit is 10.8:1 and I should think you will get close to the limit (which is good for performance). I've removed more than this from several engines and ran fine.

 

The engines are mapped at top limit so you will be safe to run it like this. It will even give you a little more power and torque. As you will have to have the valve gear removed for the skim I'd advise that you clean up the ports to remove rough casting marks and any misalignment from seats to ports to manifolds (check Dave Andrews website for guidance) . That way you will effectively upgrade your engine to an MGF Trophy 160 (phase 1) spec (get a big throttle from PTP for £100 for the full effect).

 

Bob

[oilyhands]

If the liners have indented more than about 3-5 thou then it will be soft.. especially if the gasket has failed..

 

Oily

[Paul-R]

Many thanks Peter/Bob.

 

How would I go about checking the hardness of the head face, is there a set value it needs to meet? Assume this is something for a cylinder head shop or could I do it?

[Bob Corb]

Paul

 

Metal hardness is a v simple test but you do need a special piece of kit. Basically the hardness is measured by Brinel number (?) by a sort of centre punch type gadget.

 

Bob

[oilyhands]

There are non impact devices which can measure the hardness, Pete Jones at Jondel (01933 411993) has such a device. Its the comparative hardness across the surface of the head, compared to the upper cam ladder surface that will be most telling. Typically the exhaust side of the head is around 25% less hard than the inlet (its the exhaust side that hammers and loses temper) and the material between the bores in the centre of the head usually drops by about 45%. If there is more than a 20% variance across the gasket surface then the head is a doorstop, if there is more than 30% variance between the upper head surface and the softest point on the lower, then again its only suitable for hand to hand combat.

 

Oily