Atlas Colisbro valve guides

Am considering the RGM Colisbro valve guides on my build and have read a lot of opinions on this site relative to guides. What is the preferred way to size Colisbro? Ream, hone, or both? Also I’ve read with Colisbro you can reduce clearances. What would the preferred clearance for both intake and exhaust be? Thanks

Ask Roger at RGM if you have not already. Use the Ask question about this product link on the valve guide product page.

Schwany said:

Ask Roger at RGM if you have not already. Use the Ask question about this product link on the valve guide product page.

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I have. They have been really difficult to communicate with as of late

You do need to check with RGM or someone knowledgeable with colisbro clearances.

I have a friend racing OHC Velocettes and he uses colisbro guides with minimal clearance. But he has noticed the clearance actually seems to reduce over time. I'm not sure of the wall thickness of his guides but they have proved a bit unusual in use.

But as you probably know the KPMI ones are the best , but to ream them it's another question ??

Just see that KPMI make them now in C674 bronze , which is said to be easier to ream than the famous and better C630 !!

I am looking at Colisbro guides also because they are 1/3 to 1/2 the price of the KPMI guides. The only potential problem I see is that the flange on the Colisbro guide looks rather thin.

Therefore if you run the standard insulator with the Norton spring cup, the top of the flange might be shorter than the bottom of the spring cup due to insulator thickness.

I don't have a set of these guides to measure. Maybe someone with Colisbro guides can measure the flange thickness, to compare with that of the insulator?