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Valve guides and valve seat cutting

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I have just replaced the valve guides on my 850 mk2a with colsibro guides, these were supplied  pre machined, ie the bore could not be reamed and honed to a desired clearance with the stem. The head guide bores though were good, no ovality or scoring and were good for a 1thou+ interference fit so was happy with that.

But after fitting I checked the new valve stem to bore clearance it was 3 thou, this seems a tad too much but Ive no spec on the clearance but I would have thought 2 thou on the exhaust and slightly less for the inlet.

Has anybody got the information on acceptable stem/guide clearances, not that I can do much about it now, but it would be nice to know the 3 thou is acceptable!

Saying all that its a lot better than the 5 to 6thou and bellmouths on the original guides.

Also regarding valve seat cutting I was reading the Neway manual and they recommend a 3 angle cut possibly 15/46/60.

They recommend a 46* cutter to give a 1* interference angle to promote better sealing, they say lapping is not needed and the valve is not properly sealed until the engine is first fired up and up to operating temperature when the valve will expand to give a better seal than the 45* cut would, although Ive read that some people say the valve is slightly deformed to give a better seal?

Has anyone any experience of cutting 1* interference angle valve seats, and if so  do they have the correct Neway cutter parts numbers, thanks for any info.

I did read that some of the branches have cutters available for hire, it would be the cheaper option, if anyone can help there?

 

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I had my old worn RH4 guides replaced by BLR in Wallington, Surrey about 10 years ago with their bespoke, standard dimension colsibro guides. They were machined to suit Kibblewhite Black Diamond valves and red Viton seals. The guy doing the job at the time looked at my shiny new RGM colsibro set and shook his head. I won,t repeat what he actually said but there was way too much play.

You should have minimal wobble with the lubricated valve in the guide apparently. No idea what the actual clearance figure was but the finished job had a nice precise sliding fit. 

You could contact them and ask. I,m getting my Kawasaki Z1R guides and seats done by them later this year but fitted with oversize inlets.

http://blrengineering.co.uk/

When my RH4 developed a bad oil leak I got a new Fullauto head. The valve guide fit was the same with new Black Diamond valves as the BLR job on the RH4. I hand cut the inlets to fit larger + 0.060" Black Diamonds with Neway cutters 45°/60° but hand finished the top angle into the combustion chamber. Bearing blue showed full contact around the seats and no lapping was necessary as you say.

I considered the 46° cut but stayed with 45° which works perfectly well in practice. 15000 miles down the line they don,t leak oil and the engine still produces strong hp and torque with good fuel economy.

 

 

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BLR  did a good job for me many years ago and have a long history of working on  exotic  engines.  Don't know who is there now.

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Not a Norton but I've just had some colsibro valve guides fitted to my 63 Ducati and the fit is a sliding transition fit - at a guess I would say the clearance is somewhere between zero and 1 thou (0.000" - 0.001").  The 3 thou clearance you have seems excessive and will allow the valve some side to side wobble as well as gas and fluid bypass up or down the stem.

I've read a lot about multiple valve seat angles (15/46/60) and to honest I don't think it makes a jot of difference on an old road going engine.  Fine with modern style combustion chambers and racing engines, but a waste of time and money with your engine.  I can't comment on the 46 degree versus 45 degrees - sounds like a good idea, but am not sure again if there will be much difference.  Personally, I would cut the new seats to 45 degrees and then hand blend the angles into the ports and combustion chamber using a carbide burr in a die grinder type tool, making sure that at least 2mm on the 45 degree cut is left untouched for a good seal.  As above, well cut valve seats do not need lapping in.

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Thanks for the info guys, very helpful. Talking to BLR they reckon 1 thou for the inlet guide and 1.5 for the exhaust, I think those guides will have to come out. I was considering making my own from colsibro as I did with my cam bushes but by the time Id bought the material and guide hones and seat cutters it probably wouldnt be at all cost effective. BLR seem quite reasonable

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Colsibro is only any good if you can ream them to fit after the guides have been installed, that is the idea of using colsibro, it allows tighter clearances at the expense of wear rate. It is a totally different material spec to the usual harder wearing bronze valve guide material. If you fit Colsibro with standard clearances then you might as well used cast iron guides. 

0.0003'' is way way to much as some indicated above, those behind you won't thank you.

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The G&S valves web site has a huge amount of information.  It tells us that an important aspect is material - some guide materials require stems to be hard chromed, there's cast iron, and 'bronze' which comes in many alloys, some of which are suitable for stainless steels, or chrome and so it goes on.  

Unfortunately, although they have a huge catalogue of valves, the tables don't have a column for compatible materials between stem and guide.

It seems that "Colsibro® is a high copper alloy with small additions of nickel and silicon" so it is not 'bronze' (which is copper plus tin) or brass (copper plus zinc).  

Anyway - when we come to look for new valves or guides, there appear to be mistakes to be made and I can't find the guidance I trust.  I hope our specialist retailers know what they are selling to us.

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Thanks for the info Ashley, I think they should be reamed and then honed for the optimum fit and better surface finish, the ones supplied  as you say are a waste of time because of the pre machined clearance.

I was unaware of the clearance required when i fitted them to be honest, I wasnt expecting them to be completely wrong!

I had a similar problem with supplied camshaft bushes with not enough meat on them to line bore them so made some 8 thou undersized from SAE 660 leaded bronze and line bored them to the correct clearance as mentioned  a previous post.

Talking to BLR the Colsibro clearance should be 1 thou inlet  and 1.5 thou exhaust. I was considering making some and honing them to the correct clearance but after pricing up a valve guide hone have gone off the idea!!

Its great to have this forum to get the benefit of other peoples knowledge and experience

Thanks for that David, I will have a look at their website and when I spoke to BLR they recommended G and S valves for use with their Colsibro guides

 

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