Valve guide to head fit

Hi all

I have removed the guides from my 68. I drilled them out carefully as recommended and was left with very clean bores with no visible wear or scoring. Have measured the bores and they all measure up at exactly 0.500". So my question is if 0.500" is the standard size for the bores and the standard size for the OD of the guides is 0.501" this gives an interference fit of 0.001" when it is recommended the fit should be 0.0015"

Has anyone fitted standard guides in standard size bores and had any problems. Should I fit new guides as is or machine them out to 0.5015" and fit 0.002 oversize valves giving an interference fit of 0.0015".

Is 0.0005" going to make a difference?

Thanks
Dean

Don't know if 1/2 thou will make any diff but if you get +2 thou guides why not turn them down 1/2 thou so they are plus 1.5 thou. That way your head is unchanged an od is always easier to measure.

Before you go to a great deal more time effort an expense i would ask how good your measuring equipment is as the amount of difference between what you're getting and spec is very little.
I am in no way trying to undermine your efforts but when measuring to such accuracy many thing may affect the outcome. I work in a large temperature controlled machine shop so accurate sizing of jet engine and large (10 meter plus) oil field parts is possible. The measuring equipment is also constantly recalibrated.
If you where to get a guide it may possibly not measure the spec size so it is then down to selective assembly and adjusting sizes to get the required fit.

Also when you get your new guides check they are parellel on the OD before fitting because some are not in my experience

Dean,
Heat the cylinder head to 150 to 200 degrees C. before you put the guides in as per shop manual.
Us the BBQ or kitchen stove when the wife is out. :wink:
Cheers,
Thomas

The factory spec for the 750 guide OD is .5010" to .5015" (misprinted in some service manuals as .5015/.50 in.), so your new guides are within spec. It also means that the factory fit is .0010" to .0015", not just .0015". You should be able to install the new guides with no issues.

Ken

CanukNortonNut said:

Us the BBQ or kitchen stove when the wife is out. :wink:

Click to expand...

No need to worry about using the kitchen oven, as you would have already run the head through the dishwasher!

Nater_Potater said:

CanukNortonNut said:

Us the BBQ or kitchen stove when the wife is out. :wink:

Click to expand...

No need to worry about using the kitchen oven, as you would have already run the head through the dishwasher!

Click to expand...

Meanwhile, the gas tank is wrapped in foam and tumbling in the dryer with a handful of nuts in it, to get out the remaining rust and scale...

grandpaul said:

Nater_Potater said:

CanukNortonNut said:

Us the BBQ or kitchen stove when the wife is out. :wink:

Click to expand...

No need to worry about using the kitchen oven, as you would have already run the head through the dishwasher!

Click to expand...

Meanwhile, the gas tank is wrapped in foam and tumbling in the dryer with a handful of nuts in it, to get out the remaining rust and scale...

Click to expand...

Of course if you had not wasted all your money on these domestic labour saving items. Firstly your other half would be to busy doing the domestic tasks to complain and secondly you could afford a Fullauto head or someone like Jim Comstock to do the job for you. :lol:

toppy said:

Of course if you had not wasted all your money on these domestic labour saving items. Firstly your other half would be to busy doing the domestic tasks to complain and secondly you could afford a Fullauto head or someone like Jim Comstock to do the job for you. :lol:

Click to expand...

That is beautifully politically incorrect !

Hi all

Thanks for the replies. Some useful, some not... still amusing.

I found some measurements in an online manual (see copy) so am not so confident that 0.001" is tight enough. I'm confident in my measurements. I have been measuring these sorts of things for many years as an aircraft engineer and also worked in gas turbine engine overhaul. I have good quality measuring equipment that is down to 0.0001". Also kept it all at 20 deg C for 12 hrs before measuring and all is very clean.

Will be going with kibblewhite bronze guides and black diamond valves and the bike is for street use so won't be highly stressed but kibblewhite also quoted 0.0015" as minimum fit.

I have seen in another post that comnoz quoted -interference fit.- .0015 except RH4 intake guides which should be .001 for bronze guides- they will need to be a little tighter for cast iron. It they are driven in too tight they will crack the head. Locktite will not hold. Jim

Also not sure what head I have. It is the original 1968. What is a RH4 head?

Can anyone else shed any light. I can ream the guide bore in the head if I have to as I have the tooling an skills but would like to keep it standard if possible.

Thanks again.
Dean

The rh4 head is an 850 head found on 73 and 75 models.

Glen