Buckaroo Banzi

Just spent $1271 on a brand new head and valve job the major expense besides the head itself where the intake valves the machine shop advised me to replace them at $70 bucks a pop he said they had a ( one thousands tape)r on the valve stem.

My question is could I have re-used these intake valves with a one thousands taper on the stems?

thanks,

m42racer

Absolutely. Typical rule is 0.001" clearance on the Intakes and 0.0015" on the Exhaust. If any taper is measured, the guides are usually pin fitted to the lowest dia size. Most street engines will have more than 0.001" taper. Most run Seals and most have more clearance for safety. I think you were sold Valves for selling sake. The other way of looking at it is, the stems are now perfectly straight, but are the Guide bores? There is a given tolerance here and for a street engine you were well within it. For guides or stems to cause smoke, the clearances are way more then 0.001".

Buckaroo Banzi

Dammit
I took the head to a shop that was supposed to have a lot of experiance with 951 heads when he told me they where bad and I questioned it he told they where on the edge I could use them but why take the chance? So of course I shelled out the bucks for new one's

Thanks for the input..

mark944turbo

Its usually 30 bucks each where I come from, that price is pretty high.

Chris White

You were close to the wear limit – did you want a head that was good or one that was acceptable?? If you told the shop you were using this for any performance work then they did the right thing, if you told them to do it cheap as possible then they could have left the valves as is….but who would ever figure that a Porsche Owner wanted it cheap!?!?

Chris White

m42racer

Part of quote

"You were close to the wear limit – did you want a head that was good or one that was acceptable?? If you told the shop you were using this for any performance work "

Whats the difference?

Chris White

Simple – its about the life cycle of the part. If it is near the wear limit then it is not long before it exceeds that. Call it preventive maintenance. How will the customer react when his engine starts burning oil in 6 months? That will cost more in gaskets to fix than the valves did now…

Also – if a shop is preparing something for a ‘performance’ application then factory wear limits are not an acceptable guide.

Just my opinion.

Chris White

hosrom_951

More like a rule of thumb than opinion

m42racer

"Also – if a shop is preparing something for a ‘performance’ application then factory wear limits are not an acceptable guide."

Normally, race or performance applications require more clearances, due to the increase heat etc. Valve guide clearances are not normally increased over the typical 0.001" and 0.0015" clearances. In most race applications Guides seals are neverused, due to the extra Lift and fear of them coming off. I will agree that something should always be correct, but in this case, 0.001" taper is acceptable and most engines running on the street, that do not smoke would most likely have more. This is the reason why Guides are pin fitted to the Valve stems. To control the clearance, increase it when ever required, and to match the Guide ID to the Valve stem. I have seen brand new Valves with this amount of taper. Measure the Valve stem taper and sell the customer brand new Valves with zero taper and then have a guide with the same amount of taper. Whats the difference? Holding 0.001" within the Guide ID is not as easy as it apppears. Typical is maybe 0.0005" or more, from top to bottom and in concentricity. The book is a guide line. It still comes down to experience and knowing what is allowable and what will give problems. From what was posted, the Stem had 0.001" taper and the Guide was new. This would not cause any smoking issues and would not be an issue long term either in my opinion. The Guide material is softer than the stem, and the wear will happen to the guide before the stem typically.
In this case, and others similar, the sale appears to have taken precedent over experience.

Skunk Workz

I have yet to see many applications where building an engine "loose" i.e. with bigger than stock clearances yielded anything else than problems... as in using oil,getting piston slap,wearing out bearings faster etc. A properly built "tight" engine has no problems coping with power increases whatsoever. As for 0.001 and 0.0015 being rule-of-thumb for valve-to-guide clearances...that's the rule-of-thumb of "what was acceptable in the '60's" or "limit of wear"... 0.0005 is what a new guide should have. Too tight? I've run 0.00025..."slip fit". Didn't score,gall or otherwise f**k up...

Chris White

In response to M's post -

This comes under the new acronym – “NWAA(W)”
Not Worth Arguing About (or With).

I think I will use this more often instead of just going on and on.

Chris White

special tool

Chris - that is a "service" limit, not wear limit. The additional service life from this measurement has been calculated.

hosrom_951

Just for clarification, when i quoted Chris and said "rule of thumb" i was referring to the condition being within specs as opposed to being nearly down to the limit, before going into high performance mods. This applies to almost everything (bores, rings, play and so on).

Chris White

Sure, but you never know when the customer will want to see how high his car will rev on the dyno…..

Voith

Where to buy new OE valves at reasonable price? I need 4 new intake and two new exhaust...