bobb

Hi Guys,

Excuse my ignorance here, but I've never rebuilt a set of Olds heads....so no laughing at my questions.

1. I see a set of D heads on Ebay with a cracked guide and one guide completely gone (cracked off at the base). Are the guides replaceable? Aren't they cast integral with the heads?

2. I picked up a set of used Olds heads and I noticed the valve guide holes are threaded when looking from the valve cover side of the head. Why are they threaded?

3. On the same set of heads I noticed some of the valve guide OD's are smaller than the others. I haven't measured, it's just a visual, but I'll get numbers tomorrow. Is this normal? I would assume the valve seal needs a certain guide ID to be able to stay attached to it. I can get some pics tomorrow if what I'm saying doesn't make sense.

thanks,
bob

Rickman48

Guides can be replaced, as they make a complete guide, about 4" long x 1/2" in diameter.
Once the head is set-up on the correct angle, usually on a mill, you'd drill out and ream a hole the size of the new guide, and press it in w/a locktite coating.
You'd still have to ream the new guide to the size of the valve stem, as they're undersize from the manufacturer. Good for stock heads.
The installation of bronzewall guides is close to the same procedure, but they're usually much thinner. They seem to last a lot longer, as bronze is slipperier than cast iron! Preferred for high-performance.
The 'threading' you're refering to is called 'knurling' and is a cheap way to return the guide to a specific diameter. Good for a while, if done correctly, for a stock engine.
The difference in valve stem diameters is also a way to 'save' the guide - just drill and ream to the new size - maybe a valve for another application with the same length and/or a bigger head diameter.
Seals come in many sizes - the top of the guide is machined for "P.C." seals!

bobb

Rickman48,

Thanks for the info! Just so I'm clear......what you're saying is:

Whole guides can be replaced.....not a big deal. Got it.

The threads I think I see are knurling.....makes perfect sense.

Bronze guides are a better way to go than the stock cast iron, and to install them they'd ream out the knurling and press in the new bronze guides, then ream to size....right?

As for the valve seals.....sounds like you're saying they make different size seals, so the OD of the guide shouldn't be a problem. But why would anyone machine down one or two guide OD's?

Thanks,
bob

507OLDS

When I have had iron heads redone,the cast guide bosses get removed when the new guides are installed,so seeing a head with a few broken-off is nothing to worry about.Chances are,the valve was rusted in the guide,and they broke it off trying to pound it out.What you need to make sure is that the head itself didn't get cracked in that area.

bobb

Brian,

Thanks for the info. What I was thinking was knurling was actually the factory serrations in the guides. I didn't know the guides had that type of surface finish from the factory until I described what I was looking at to a friend. I checked the OD of the two guides that were replaced and they measured about 0.507. Looking around I see there are valve seals available for that OD. Why they didn't press in guides with the same OD as all the others is a bit of a mystery, but who knows?

thanks again,
bob