View Full Version : Identify exhaust valve

12-03-2009, 08:42 PM

The head from my BN1 is being repaired and the guy from the shop asked me to supply 1 exhaust valve and 1 inlet valve. However the exhaust valve is different to whats on the head. The valve is larger, 2mm in length and 3mm across the valve. The original valve is stamped with what looks like MOWCO AEC 9/5

Can anyone identify this valve and is it common to increase the exhaust valve size on the 100 engine. The inlet valve was the same.

Cheers Graham

12-04-2009, 03:38 AM
Hello OZ BN1,

Nice to see you're still around here.

The larger head diameter can always be machined down to the same as the original diameter.

Where is the valve longer?. Is it (a), in the distance from the top of the head to the bottom of the collet groove. (b),in the height of the collet groove?. I'm thinking (a). If this is so then install a 2mm hardened steel washer under the valve spring seat and that should take care of that.

I would like to think there would be enough adjustment in the rocker adjusting screw to take care of the extra length.

Installing larger exhaust valves is in no way detrimental to the health of your BN1.

If the shop that is trying to do the work cannot figure this out I would seriously think about taking it to another shop.

What part of OZ do you live in?. I'm sure you told me before but I've forgetten.

Best regards,


12-04-2009, 03:52 PM
It appears to me that the new valve is smaller than the original, if so, then Bundyrum is addressing the opposite issue. OZ BN1 should reword his question to make it clearer.

12-04-2009, 05:19 PM

Yep the new valve is smaller than what is installed. Sorry for the confusion. Sort of why I put the photo in but oh well. The new exhaust valve is the correct one for a standard BN1 head according to the supplier, but is smaller than what is presently used. The valves installed have an extra 2mm in the collet groove, increasing the total length by this 2mm and wider across the valve surface by about 3mm.

The guys doing the repair work, small crack between 2 and 3 cylinders suggested that 1 exhaust valve and 1 inlet valve needed to be replaced. I purchased the valves and this is when we realized something was wrong. At first I thought they had just supplied the wrong exhaust valve.

So I guess at some stage in its life a previous owner has had all the exhaust valves replaced and had the head machined to take larger valves. The inlet valves are still standard. However does not appear to be any other work done to the head, no porting or polishing. Seems a bit odd to me.

Finding a replacement valve this exact size will be difficult unless someone recognizes the part number. My options will be to purchase another inlet valve and have it machined down to suit.

Bundyrum, Adelaide Hills, my Healey slowly coming along, If I can ever get this engine back together that is.

Cheers Graham

12-04-2009, 05:21 PM
The nomenclature on the photo and in the wording do indicate the new valve is smaller diameter head AND shorter in length.
Spring tension could be an issue, along with installed valve stem height.
The possibilities are that the valve in the vehicle is too big.
If the pattern of the seat on the new valve face is in the middle of the face, no problem.
If it is all the way out to the edge, a burned valve is a very good possibility in the very near future.

12-05-2009, 01:03 AM
Hello OZ BN1,

You should still be able to buy a blank unfinished valve that is usually about 150mm in length overall. They are available in any head diameter and what the shop does is machine the valve head diameter to suit whatever size the old one was and machine the collet groove as well.

Any competent machine shop should be able to do this without any problem and so should the people that are doing this for you.

Repco used to sell blanks. What about Adelaide Engine Services are they still around.

Are you in the SA Healey club?, someone there should know this one.

What part of the Adelaide hills? I have a house there.

Best regards,


Healey 100
12-06-2009, 03:08 PM
When I had the head reworked on my Healey 35 years ago, I had the same problem. Some larger exhaust valves were fitted from who knows where. There are many valves available with the same stem diameter and length, I think the previous owner wanted larger valves to increase performance -- or, he could not find original replacement valves and went with these. The keepers on the odd valves were not the same as the original Healey intake valves.

My machinist ended up shrinking the seats with carbide inserts and fitting new original Healey exhaust valves. This setup worked for many years.

You can probably find replacement oversize valves like the ones you have if you can find dimensioned drawings from valve suppliers. Some auto parts stores still have books like that.

Good hunting!

12-06-2009, 10:21 PM
Thanks for the info. I will shop around for an oversize valve.

Bundyrum, place called Blakiston, not far from Littlehampton / Nairne.

Cheers Graham

12-07-2009, 01:04 AM
Might it be MOWOG? "Morris Works Garages"
Methinks I have larger 100/6 ex valves in my BN1
Hope to be passing through your way in lare March on way to Ballarat

12-07-2009, 01:57 AM
Hello OZ BN1,

I lived in Adelaide from 1978-84 when I was in the RAAF at Edinburgh.

My BN1 covered many enjoyable miles through those hills in that time.

Best regards,


Bob Hughes
12-07-2009, 09:18 AM
Are you sitting comfortably ?

You could be looking at a competion valve, SC Parts have them in stainless in their competition section at 39.7mm and the cost is 26 plus a bit stirling each, with the dreaded VAT on top ( they also do a 41mm ). If you are going down that road, get the full spec off them first to check everything else, it is a lot of money when standard is around 6+

You can check on the inlet valves too as they are also mentioned at 46mm .

You can get them on the webb - SC Parts and go to the competion section / B1 - B2 cylinder head


12-08-2009, 03:47 AM
Hello Bob Hughes,

When parts get delivered outside of the UK VAT doesn't get charged.

Best regards,


Bob Hughes
12-08-2009, 10:38 AM
Thanks Bandyrum, I have never had to have the pleasure of purchasing from the UK whilst abroad so I did not know about that.

Still a pricey valve though, even with out the VAT


12-11-2009, 11:34 PM
Re OZBN1's location: I know the Littlehampton area. Several of us members of the Queensland club billeted with Bob & Robyn Upton just before the 2006 National Rally which was located at Tanunda in the Barossa Valley. Fond memories.