Morris Minor Owners Club

hi all interesting one this , 1098 engine unleaded head , i just had an exhaust valve stick open , i thought head gasket when it lost power but i soon found the valve plus you could hear it firing into the exhaust manifold [valves and guides under 500 miles old ], i was not far from home so pushed on and it fixed itself after 5 miles and ran fine again !!,i replaced the last set of exhaust valves and guides as they had started to pick up in the guides at about 1000 miles and i removed the valve stem seals to help with lube , engine is now sweet as before i am thinking parts quality issues anyone had a similar problem

That's a weird one Martin I'm glad that it wasn't a head gasket problem, I wonder if there is some lube that you can use to avoid the problem happening again?

One that plagued me for a long time a few years ago.

Unleaded fuel runs 'hotter' than the old leaded fuel, so standard cast iron guides running with standard guide/valve stem clearance do tend to 'pick up', especially during the 'warm up' phase before the thermostat opens.

Some questions:

You do have a thermostat fitted don't you?

Which exhaust valve 'stuck'?

Do you have the bypass hose fitted to the water pump?

What cam is fitted? If it is standard, then set the exhaust valve clearance to 0.015".

What material are the valve guides made from? For an unleaded head, they need to be bronze, not the standard cast iron.

You have already removed exhaust valve stem oil seals?

question answered they are cast iron guides the same the ones i replaced ,cylinder 3 was / is the culprit it makes sense now

Martin,

Before rushing out and changing the guides, what are the answers to the other questions? You may get away with it, if everything else is spot on.

everything else is spot on , so i am sure its the guides at fault

The biggest problem with unleaded fuel is that it is dry - by that I mean it has no lubricating qualities. The lack of lubrication can lead to sticking valves.

Valve stem seals should not be fitted to the exhaust valves/guides as they do require some oil to find its way to them for lubrication.

Valves should have adequate clearance between stem and guide and exhaust valve guides can be reamed to provide adequate clearance. See workshop manual for details.

The valve stem should drop straight through the guide without showing the slightest sign of hesitation or stickiness.

See also:-

https://www.calverst.com/technical-info ... and-usage/

A question of how you fitted the new guides might be appropriate. Did you ream the guides after fitting? Especially important if the guides were not fitted in an ideal fashion (thumped in with a hammer, for instance).

Only once have I had a sticking valve - as soon as the engine warmed up a bit. Oversized valves (the stems) fitted to a ‘warmed’ engine and insufficient clearance. No guides fitted on that head - valve stems ran straight on the head. Removal of stem seals solved the problem without recourse to easing the clearances further, before there was a risk of further damage.

The dimensions for a suitable valve guide fitting tool are specified in the BMC workshop manual. They should be pressed in with the tool and if necessary reamed. The valve seats should be recut to be concentric to the valve guide.

In addition to the valve guide tool I made a sleeve and top plate so that all of the valve guides are fitted to the same height above the valve spring head seat.

Phil,

I’m intrigued by the machining/gouging on that head. Extra drainage channel for oil?

RAB

The groove is there as a normal part of the head casting but has been made deeper - why I do not know - the head was fitted to a 1275cc Midget engine I acquired some time back - the engine had been played around with and various thing done to it before it came my way.
The groove is next to the inlet guide and may have been made deeper to get the oil away from the guide quicker. The guides are replacements, the originals were badly worn.
I was only ever after the crankshaft which was in good condition. The rest of the engine has been dispersed in several directions. The block ended up in a replica Lotus 11.

i pressed them in using a similar tool i made to get the correct dept , i didn't ream them as they had just permissible clearance , i am 100 % sure it/'s the mismatch of materials , checking with mini spares they say unleaded spec exhaust valves must use bronze or other alternatives to the cast ones so i will run it locally just to see if it happens again i also think given the total power loss 2 valves had stuck but one had freed of before it could have a look i might be wrong but we will see

Not sure if it's general knowledge but you can still make your own 'proper leaded' fuel.
www.tetraboost.com
The original upper cylinder lubricant? Tetra Ethyl Lead

Alan

quick update its running fine , it had a reasonable run this eve and its a hot day but no issues , the plot thickens

another update .its still running fine and i have put some redex lead additive in the fuel just to help so i am leaving it well alone

Thats good news Martin and Im sure the Redex will help too.

update update ! well it looks like the redex additive is doing the job , i have done over 100 miles today and my car has never run so smoothly even in traffic and several hot restarts its perfect