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1275 valve stem seals

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Sarastro

Sarastro

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I've noticed that two different kinds of valve stem seals are used on 1275 heads. One is cup shaped, and the other is just an O-ring slipped over the stem. So, a couple questions:

1. Does the O-ring really do anything? Seems it might seal a bit at the point where the valve is completely open, but nothing else.

2. It seems to me that the cup shaped seal might seal too well--I mean, to the degree that ever happens in an LBC. I imagine the valve still need a bit of exposure to oil, to lubricate it in the guide. Doesn't this kind of seal prevent that?

3. The head I'm working on had the O-ring seals on all valves. The gasket kit I bought has only four cup-shaped seals, presumably for the intakes. Is there any reason to put seals on the exhaust valves?
 
There are actually more possibilities than that.

I believe that O-ring seals were used on the very earliest applications. BL/Rover replaced those with a more traditional seal. That gave way to a seal with a garter spring. There are also garter spring seals made with Viton.

Most people I corresponded with when rebuilding my 1275 said to use the garter spring equipped seals. Todd Miller (an Austin America owner) sells the Viton seals on eBay but probably sells them through his web site as well.
https://www.austinamericausa.com/
Look down the left side of the opening page, click on the "reproduction parts" tab and scroll down towards the bottom of that page for his Viton seals.

Here's a picture of his valve seals...
https://members.tripod.com/austin_america...lvestemseal.jpg

EDIT: The stock build of the engine only placed seals on the four intake valves. You can fit seals to the exhaust if you really want to. However, if the guides are still in good shape there is no need and in fact you may not want to prevent a little oil from lubing them.
 
I only repalce with posi seal ( the cup style that fit over the guide and use bronze guides, I only install the seal on the intakes as well, bronze doesn't need any lubrication. Even thought the posi type seals do a very good job of sealing the guide and valve, there still is some oil getting to the guide.

I'm doing this exact job right now on Ray's motor, I ported it last week, dropped it off for some harden exhaust seats, went back blended the seat edges in the ports, have shorten guides , reshaped them (bullited them) fitted the valves to guides, cut three angle on the seat, and two angles on the valves, and lapped the valves. The head is now sitting in fresh paint, should be dry by the time I get to the shop this morning, so I can now start weighting upp the valve springs to set my seat pressure, and start final assembly of the cylinder head.
 
Hap, what is the correct clearance between the valve and valve guide? .0005"?
 
Dadandson said:
Hap, what is the correct clearance between the valve and valve guide? .0005"?
Click to expand...

That's a little tight, say about .0015" on cast iron guides, and .0025-.003" on bronze guides, that works for me. Alot folks over the years have seized exhaust valves with bronze guides giving them too little clearence. I use a
.280" reamer and then finish with a 7mm flex hone, they are going to expand (or tighten up) under normal operating temps, so you need to account for that. Hope that helps.
 
Steve, since I'm doing this right now, it's pretty easy to give data, on Ray's head right now I using Moss part# 297-635, they are labled as umbrella seals by Moss, but they are posi seals, meaning they slip over the top of the guide and stay there, not ride up and down like a Chevy V8 umbrella seal. I also use ones from Honda's from time to time, but the Moss part number works fine and is readily available from all the British part vendors.British Parts Northwest who is a supporting vendor here should stock them, and on your coast. I get my on this coast from Gordon at the B Hive, which alot of folks don't know Gordon stocks a good bit of Spridget parts, and has some offerings others don't have.
 
Thanks, guys. These little mysteries are really puzzling first time I encounter them. Nice to have people around who have been through them a million times.
 
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