Hi,

Recently my Mini Van has been displaying the classic symbols of valve guide or stem seal wear. On start-up and over-run it develops a smoke screen.

Today I took off the head to investigate. I removed the valve springs from a couple of valves to check the seals and guides.

If I attempt to rock the valve side to side with the valve head clear of the seat I can feel some movement. Not a lot, but definitely noticeable.

Should I have new guides fitted or just fit new stem seals?

Usually when I build an engine for any car I send off the head to be fully reco'd professionally and simply clean it and bolt it on. This is what I did when I built the van's engine just 20,000 miles ago.

The oil and filter has always been changed every 3,000 miles or six months since the rebuild. The bores look perfect with no lip and no scuffing at all. The piston tops and valves are not excessively carboned up and are a uniform brown colour. If the guides are worn, I would have expected them to last much longer.


Cheers,

_________________
Brett Nicholson
Greendale (near Ballan) VIC.
1971 Morris Mini Moke
1966 Austin Mini
1965 Morris Mini Traveller
1973 LR Series 3 88
2007 LR Freelander 2

Brett,
The valves usually wear more than the guides do. Measure them and compare with unworn bit at top.

Standard guide bore is 0.28125" (9/32"). Running clearance is provided by the valve stem size.

I always ream new bronze guides with a 9/32" solid reamer after fitting. Cast iron ones are usually OK as supplied.

re the seals- I put 1275 ones on smallbores too. They stay there even without the grooves in the guides.

If you fit new guides to a smallbore, use 1275 ones but shorten them 3mm.

I use 8 seals with iron guides, but with bronze I just put seals on the inlets. Bronze exhausts like a bit of oil for lube...

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc.

It's a shaved 12G295 head on a 40 thou over 1098 engine (1132cc) with Heppolite pistons, wade 104 cam and a balanced bottom end.

The head currently has the 1275 type stem seals on all the valve guides. The guides appear to be bronze 1275 ones as they have the lip for the stem seal at the top.

So, if I'm reading you right, I need either new guides OR new valves if I can detect any movement? I need to know so I can have the head dropped off ASAP.

Until the Mini is back on the road, I'm riding the bus!

_________________
Brett Nicholson
Greendale (near Ballan) VIC.
1971 Morris Mini Moke
1966 Austin Mini
1965 Morris Mini Traveller
1973 LR Series 3 88
2007 LR Freelander 2

From memory, stem clearance on the exhausts with new valves is about .002".
If they feel loose and the valves are not worn when checked with a micrometer, I'd fit new ones.
But if you use new bronze guides, they MUST be reamed after fitting- as they close in. If they grab the valve at high rpm it's not a pretty sight.

These days for road cars, I prefer iron guides, unless running S/S valves (as I am).

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thnaks, I dropped it off at the head reco place this morning. I pointed out it had only done 23,000 miles since they last reco'd it. They promised to dig out the old job card and have a look at it today. (They stamp the job card number on the manifiold face of every head they do!) I'll see what they come back with.

Cheers,

_________________
Brett Nicholson
Greendale (near Ballan) VIC.
1971 Morris Mini Moke
1966 Austin Mini
1965 Morris Mini Traveller
1973 LR Series 3 88
2007 LR Freelander 2

The head came back with a perfect report. Dead straight and all valves sealing perfectly.
The valve guides and valves came back well within tolerances. The stem seals were a little hard, but not excessively so. But while the head is off, I'll replace them anyway.

EDIT: Guides are confirmed as 1275 type cast iron ones.

The only thing I can think of now is glazed up bores, or perhaps an oil gallery was leaking into the combustion chamber? The head gasket was weeping a bit.

* 175psi on all cylinders, tested hot, adding a little oil does not cause the compression figures to jump.
* The head and psiton tops were not coked up, so no reason to suspect gummed up oil rings.
* No booster, so no brake fluid entering.
* No blow-by.
* It consumes some oil, but not excessive (maybe 1-2L over 3,000 miles) and it does have a couple of minor leaks.
* No blocked breathers.

Is there a "home brew" glaze busting technique I can try without diassembling the bottom end? Someone suggested a very small pinch of AJAX chucked in the intake at idle will clear bore glazing, but I don't want to perform an "instant rebore".

_________________
Brett Nicholson
Greendale (near Ballan) VIC.
1971 Morris Mini Moke
1966 Austin Mini
1965 Morris Mini Traveller
1973 LR Series 3 88
2007 LR Freelander 2

Sounds pretty good to me, for an A series..
A friend bought a NEW Morris 1100 way back when, and it was getting about 400miles/pint of oil. When he complained to BMC their response was `It is normal, Sir'...
Standard 1275 valve stem seals go hard pretty quick. The later `Metro' ones with the spring last a little better, but basically even their material is still crap...

PM sent..

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.