Morris Minor Owners Club

Albert's been running a bit rough recently so I took the head off to try a decoke.
This is what I found on the inlet valves of cylinders 1 and 4

Don't worry, i kknow this looks like serious valve seat recession but it's actually oil. Would I be right in thinking this wet ring of deposit is indicative of failing valve stem seals? Could it be anything else - the bore look fine?

Also, the back of the exhaust valves seem a bit unusual. I've never seen
the extra step/angle change like this

Could the exhast valves be rimflo ones? .or may have just been back cut by a machineshop

It would be interesting to see a couple more pictures of the head/ combustion chamber as that exhaust valve looks like it may have been worked on to improve the breathing. That inlet valve "ring" looks odd, yes probably valve seals causing the oil, but looks odd somehow. Any hope of a close-up?

Valve looks normal enough to me ! Have you been using additive?

I can't really tell what I'm seeing in the 1st picture (what is the silver looking ring?), if it's the valve seat it's horrible.
Exhaust valve looks fine.
The symptom of bad valve seals is normally blue smoke on start up after sitting over night.

The throats of the head are unworked. They still exhibit the casting imperfections.


These are the inlet and exhaust valves. the inlet is nice and flat, the exhaust shows that curious step.

Rimflow inlets have an anti-reversion grove on the face of the inlet valve head - so my inlets appear standard. Is this step the comparable shape for the exhaust valve? There again I wouldn't expect to see performance valves on an unworked 'small valve' 1275 head.

The (alloy) inlet manifold is squeeky clean with no trace whatsoever of oil from crankcase oil pressure.
Also I've enlarged the 2 original photos. The silver ring is not recession - it's shiny black oil

The valves look fine, and the seats.
If you put the valves back in without the springs then "open" them the amount the cam would do, how much sideways movement is there in the valve head?
As the inlet manifold is clean the valve seals and the guides must be suspect.

Perfectly normal valves - but there does seem to be quite a bit of oil in the valve throat area.

Seen load of valves like that Pete, it may be an A+ thing?

Doesnt preignition cause erosion on sharp edges - like where the silver ring is?

like where the silver ring is

As mentioned previously, it's not silver it's oil reflecting the flash gun.

What type of valve stem seals are fitted and what condition are they in? Rock Hard?
Is there play in the guides?

I discovered yesterday that there is noticeable play in the valve guide and I will be replacing these too. I have a set of guides but remember trying to fit them to an old head and they were slack enough to push right through. Sounds like there are two sizes for these but no retailer I have found so far can confirm this in their part list. Any comments?

No - all the same diameter over the years (MG Metro Turbo excepted) - but there are length variations. You need a stepped drift to fit them - some heat the head up in the oven before fitting the new ones to avoid having to batter them too hard! I have never done this - my domestic life is hard enough as it is !! Best to remove/refit one at a time - using a steel rule across them to get the level for the new one - then move on. You may find you need to ream the new guides once installed - if you damage the end in any way. A good fitting new drill bit hand-held is usually sufficient!

Cheers BMC.

A good fitting new drill bit hand-held is usually sufficient

Do you mean just the end that's been damaged?

Well - the Mini lads insist on reaming the complete guide as being necessary - I have never found that. Just the end if it gets slightly 'swollen' - but a proper stepped guide insert tool IS necessary - unless you can heat the head enough to get the new guides to just 'drop in' - obviously you don't care what happens to the old guides as you bash them out! You do need to be sure the new guides are very firmly held in the head - obvious disaster if they come loose!!

Oh yes!

I'm going to assume that the guides I have were wrongly supplied and have ordered a new set in phosfer bronze.
Had a word with a 'cheap local engineer' too and he's agreed to do some basic port work to open out the exhausts as they are just ridiculously narrow around the bosses.

Yes - that is where to do the work on the exhausts - otherwise the head is very good. Phospher bronze - hmmm - less likely to seize etc - but not the best for wear!! Usually only used on highly modified engines where the valves etc are under considerable stress - and the head is rebuilt regularly. Standard guides are best for standard heads/use. Your head isn't a Turbo head is it ? They do have larger guides to suit the larger stems of the sodium filled exhaust valves !

It was the spare heads that dropped the guides - the holes in the head were only just too big - you could just push it through with your thumb but you wouldn't want to do it too many times. As far as I can recall the thing looked standard. It was unworked and had large valves (inlet and exhaust almost touch) I believe the turbo heads had the smaller valves (standard early 1275).

Yes - turbohead has the smaller inlet - all exhausts are same (except early genuine Cooper S heads!). The turbo guides are significantly bigger - I believe.

If you are going to employ an engineer why not get him to put bullet ends on the guides before he fits them?
My brother in law managed to do this and he is more of a bloke with a lathe than an actual engineer