Cylinder Head Refurb.

[Chazbee]

I’m refurbishing a 12g202 head for my 1098cc engine and I have a couple of questions :-
When I have the face skimmed should I just have it cleaned up or would it be a good opportunity to raise the compression ratio a bit? How many thou should I remove?
If I turn the engine over with the underbonnet solenoid switch when the head is off and the push rods removed will the cam followers stay in position or is there a chance they might become displaced?

[philthehill]

Measure the depth of the head first which should be 2.75".
If the head is 2.75" I would suggest taking 0.060" of the face of the head.
If you turn the engine over there is a good chance that the cam followers becoming displaced.
Take the side covers off and remove the cam followers but keep in order so as to put them back as was.

[liammonty]

I'd be wary of taking too much off the head - the compression ratio on a standard (HC) 1098 is already 8.8:1 and if you go much higher than that, you'll need to run on super unleaded, or retard the timing a little to prevent pinking. Retarding the timing would of course negate the benefits of increased compression. I previously skimmed too much off a 12G295 head which gave a static compression ratio on the engine to which it was fitted of just over 9.5:1 and it was too much for a road car on today's fuels. You'd get away with a higher CR with a longer duration cam than standard, though.

[Chazbee]

Thanks for replies - as in many questions there are varying opinions but I’ve now got food for thought!!

[don58van]

Hi Chazbee

Please keep us up to date with how you go!

[Chazbee]

After completing the job (new guides,springs,top hat seals on inlets,rocker shaft and a light skim) I decided to check the handy work by filling the chambers with parrafin to check for leaks. I filled them right to the brim and after 10 mins there didn’t appear to be any leakage however after 1hr there was discernible wetness in all ports. I’ve checked again today after 24hrs and no.1 chamber is almost empty so a revisit required there but the other 3 chamber levels have hardly moved - 1mm at most. Would you consider the performance of the 3 chambers to be satisfactory or should I be looking for totally leakfree valves?

[philthehill]

Paraffin is very thin and you are bound to get some leakage past the valve seats as the valve to head seating is not a precision fit/seal, it is the best you can make it fit/seal. I would re-visit No: 1 cylinder and lap in the valves again but the other three I would not worry about a dampness in the ports but if you want to give them an extra lap by all means do so.
As you have fitted new valve guides did you cut or reface the valve seats to the new guides?
When new guides are fitted the valve seats should be re-cut and centered to the new valve guide. Not all new valve guides are centered on the valve guide hole in the head.
For general information - Top hat seals should only be fitted to the inlet valve guides. The exhaust valve stems/guides need all the oil they can get to lubricate the stem and stop the valve stem seizing in the guide. Unleaded fuel has no lubricating qualities to speak of.

[Chazbee]

Thanks for the response/reassurance - my valve lapping skills are not as bad as I feared. I’ll definitely be looking at no.1 again - It appears to be largely leaking through the exhaust valve. I didn’t have the valve seats recut - I was prepared to do so but as all the valves and seats appeared to clean up nice and evenly with course then fine paste I assumed everything was OK - presume that in this case both the old and new guides were made accurately (apart from no.1 exhaust maybe!) I only fitted new style seals to the inlets but fitted the old style O rings to the exhausts - probably don’t do much but seemed like a reasonable thing to do!

[philthehill]

The valve guides in the link below are the ones to be used with the top hat seals. Note the groove that retains the seal on the guide.

https://www.morrisminorspares.com/engin ... l-p1209547

[Chazbee]

Those are the ones I used but I first machined them to the same length as the originals - I think they’re supplied to fit all the A series heads including the 1275cc which I believe need longer ones. It would be a bit annoying if you didn’t have access to a lathe although I suppose you could let the extra length poke into the port - not good for gas flow though! The new design seals have a little lip on the bottom edge which fits firmly into the groove on the guide and the other end fits snugly round the valve stem held tight by a wire spring - they seem to be a properly engineered solution which the small rubber O rings definitely were not!!

[philthehill]

The valve guides in the link below are the ones for the 1275cc 940 head. They are slightly longer than the 948cc/1098cc valve guides in my link above.
https://www.morrisminorspares.com/engin ... c-p1180438
The 1275cc valve guides have to shortened to suit the 948cc/1098cc head. The inlet valve guides can be machined with a taper to reduce the restriction to gas flow in the inlet tract as per the lower guide in the picture below.

Valve guides and tool.JPG (445.66 KiB) Viewed 1221 times

[Chazbee]

I guess ESM sent me the wrong guides - I definitely ordered 1098cc ones as in your first link - just checked my order! Something for people to watch out for when ordering!