Don Terrill’s Speed-Talk

A question about valve guide work. It's clear I need to do something to my guides as the clearance seems to large. Usually this is a new guide, but a costly affair. Is a valve with an oversize stem a possibility here along with reaming/honing the guide to size ? If so what is involved and what needs to be changed as well ?

Personally I've never seen an oversize valve stem as a solution for too large a clearance. If one were available I'd imagine you'd need different locks perhaps (not sure). Either way, it seems that the cost of having the guides honed to a next size up for a larger (+.00xx) valve stem, if such a beast exists, then purchasing valves to fit, would surely be greater than having new guides installed and honed to the correct clearance. Plus, you need to factor in the additional weight on the valvetrain if you go with a larger valve stem. This would be a bad thing if you're spinning the engine to any substantial rpm.

Why not k-line or similar?
This works very well when properly done.

nickpohlaandp wrote:Personally I've never seen an oversize valve stem as a solution for too large a clearance. If one were available I'd imagine you'd need different locks perhaps (not sure). Either way, it seems that the cost of having the guides honed to a next size up for a larger (+.00xx) valve stem, if such a beast exists, then purchasing valves to fit, would surely be greater than having new guides installed and honed to the correct clearance. Plus, you need to factor in the additional weight on the valvetrain if you go with a larger valve stem. This would be a bad thing if you're spinning the engine to any substantial rpm.

Ok, thanks

It took me a long time to figure out how important guide size and prep is to power, oil control, detonation resistance, tune and durability. Pay to have it done right.

At one time Ford sold valves in .003 and .015. Bill

Sealed Power, Enginetech etc sell valves with oversize stem, .015" for sure, not sure about other sizes. Some "rebuilder" valves are .030" over on diameter too.

Dave

There are valves with oversized stems available to PERs (production engine rebuilders). I've run into heads with them but haven't used 'em.
Agree with replacing or relining the guides with K-line sleeves. Done right they will run a long and happy life.

Oversize stems can be a lot of trouble, may need oversize keepers to match, have to buy a lot of new valves, but really is nothing wrong with the concept in the short term.

If you come across a head with oversize stems and the guides are worn.....usually end up replacing all the valves and guides, which of course is a lot of $, but maybe you can save the valves and put them in another head
The cycle of hate continues

any oversize stem valve i have ever seen has only been oversized on the stem, the keeper groove location is stepped down to std size so no special keepers are needed.

kind of like a nissan SR20 - 6mm inlet 7mm exhaust, both valves are 6mm at the keeper grooves. the old RB30 did similar but with 7 and 8mm.

I don't know what you mean. Would you like to see one? or..... just making fun of America.
Go ahead we deserve it, that is a stupid idea.
You may need an oversize seal too, once up to 0.381mm over

modok wrote:I don't know what you mean. Would you like to see one? or..... just making fun of America.
Go ahead we deserve it, that is a stupid idea.
You may need an oversize seal too, once up to 0.381mm over

Just a joke! undersize stems and valves also. Undersized valve requires a smaller keeper, otherwise can't get it in the hole, unless you use ford's split guides
Undersize oversize and offset....the catalog is overloaded, too may kinds of them, they keep multiplying
Standards are good, might be a part of making the world civil.
Oversize stems and piston pins and king pins SEEM like a great idea but once they are OUT there it results in much chaos and confusion, so avoid when possible.

All the keepers I have seen for 11/32" & 3/8" stemmed valves would accommodate a 0.015 - 0.003" increase in stem diameter.

We occasionally get a previously rebuilt cylinder head in here that it is some odd oversize valve stem that we don't have a pilot for. Most likely from a high production engine rebuilder. Make sure you have a pilot before you choose a oversize.