Valve Guide Clearances

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Jan 4, 2012
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Is there any difference in the max-min clearance, between Cast Iron valve Guides & Bronze valve guides?

For Cast Iron the specification is:
Valve Stem: 0.3090” – 0.3100”
Valve Guide: 0.3145” – 0.3135”
Clearance: 0.0055” – 0.0035”

But, I can find no such specifications for Bronze.

Any suggestions?
 
I've been running .0015" on the intakes and .002" on the exhausts for bronze guides in my race Nortons for decades, and never had any problems.

Ken
 
Looked round the forums found nothing, anyone want to 'splain if we can look at valve-guide clearance using a dial indicator and measuring the sideways movement of the valve? going through a 31K indicated 73 850 thats had "unknown" work and I have apart cuz 0L - 80R compression? kinda looks like something may have bounced around the LH chamber prolly beofre a rebore and new pistons rings were done. The pistons skirts really got scored were transferring aluminum to the bores Bore gauge says the bores are still pretty decent with less than .0001 max diff in either bore LH exhaust valve/seat faced were heavily carboned up.

Valve Guide Clearances


Valve Guide Clearances


Valve Guide Clearances


So yeah looking for some thoughts on how to proceed.
 
L one looks a bit like my 74 when I tore it down a few years ago. I don't have any of the piston wear marks.

I had to go from .020 in the mid 90s to +.040 due to a bit of rust pitting on the bore for sitting idle for 10 years not to far fom the Pacific

Proceed +.020 and a new cam. New shell and bearings and balance your crank since everything will be apart.

.
 
Hi , I worked as a Automotive machinist in the 80s 90s , I used to rescue quite a few siezed barrels and didn't hone the alloy out , (didn't want to increase bore size too much )but found using a glass bead blaster will remove the alloy from the bore , then just gave them a light power hone with sunnen an200 stones , I was reading someone does a bsa cam lobe and radiused followers usa I think .also with the valve clearance most manufacturers have the desired clearance on the part., piston or valve i:e stem size is smaller than the standard size reamer . Cheers
 
Hydrochloric acid will remove alloy from steel/iron and leave the steel/iron unaffected, used the technique a few times on Briggs cranks where the alloy rod runs directly in the cast iron crank and seized. Just brush on and leave until the fizzing stops.
 
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