Valve guides

Don't forget that the new guides will probably cause the valves to become off-centre and so re-cutting of the seats may be necessary.

Other things to check before fitting guides are;

Size/ovality of the hole the guide is going into.

Outside dia. of guide to determine interference.

Once the guide is fitted the internal bore becomes hour-glass shaped. The internal bore should be undersized so that it can then be reamed/honed to match the valve stem dia. and achieve the required stem to guide clearance.

Totally agree there is great satisfaction doing a job yourself - as long as you have the required tools to do the job properly.

Hello yes like a good set of valve tools and valve seat cutter , Some Branch'save theses item for load for a nominal fee I would Urge all branch's too try and get these Valve tools and a Good set of Valve seat cutters maybe some of the EC member could help with some of the funding for smaller branch s or add some advice on how too fund these items And I now only fit Bronze Valve Gudies Has the Cast iron ones are just not up too the job and I had them brake in side in the head for No reason and they do make a mess of your cylinder head I managed too save My cylinder head buy making my own tooling ,and over size valve guide in Bronze too suit , yours Anna J

A friend with racing experience with cammy Nortons, who is a toolmaker as well, says the stuff for valve guides is COLSIBRO bronze, which needs barely any lubrication and so tolerates clearances down to 0,0015" without trouble. As Dommies seem to have lubrication problems in the valve area maybe his advice is sound,

Ideally you need to drift the new guides (head already heated) down over a valve stem to make sure it is aligned properly. This means using a tubular drift and timber packing under the valve head to hold it in position. It's worth it if you want to avoid a guide going in on the skew. It's fiddly to start off because the valve stem has a large hole to flap around in but once the guide has started in its bore it should self-align as you drive it further in. The Jaguar XK straight 6 engines use the same diameter/bore guides - yep, really - and if you're not careful you can drift them in well of square. I know this because I've done it! I used the Norton valve guide drift on the Jags. Small world eh? I can remember when Pride & Clake's used to advertise valve seat cutters with 45 and 30 deg cutters for peanuts back in the 60s! Shame I never bought one!

Valve guides should be pressed in to a heated cylinder head using the appropriate tool, especially on heads where the port wall thickness is marginal and unequal i.e twin cylinder Norton's.

Andover Norton part number 06-3964. Suitable tools also available on ebay.

I don't know the dia. of Dommie valve seats but for optimum gas flow a 3-angle seat is recommended, 60deg blends the seat to the port, 45deg is the valve seat and 30deg blends the seat to the combustion chamber. Neway are very good quality seat cutters.

Previously simon_ratcliff wrote:

I don't know the dia. of Dommie valve seats but for optimum gas flow a 3-angle seat is recommended, 60deg blends the seat to the port, 45deg is the valve seat and 30deg blends the seat to the combustion chamber. Neway are very good quality seat cutters.

Hello yes Neway are good set of valve seat cutters and will only cost you £660 a set you need to do a lot of valve seats to justify the cost yours anna j

Previously simon_ratcliff wrote:

I don't know the dia. of Dommie valve seats but for optimum gas flow a 3-angle seat is recommended, 60deg blends the seat to the port, 45deg is the valve seat and 30deg blends the seat to the combustion chamber. Neway are very good quality seat cutters.

There is another way to treat valve seats, for those that are nursing along an old machine and don't require maximum power output: I try to make my exhaust valve seats offer the largest seating area for the valve. I get maximum cooling and I sacrifice some power. It is not "the right way" though. Also, if the seat area is wider than the valve, the valve might recede into the seat which is not good.

Very useful information/video.

https://www.youtube.com/watch?v=Q5kC3AaUug0

Previously kevin_wood wrote:

Thanks everyone.

I have worried all week and re-done the exhaust valves tonight with cutting paste. It has worked, but took along time.

I have only done this sort of thing once before, but on a more modern head.

I turned the head upside down and locked it in the vice. I filled the cups in the heads up thinners, not leaked a drop in an hour! Result!

YES that how you do them I put a tad of engineers blue in my white sprites it leave a blue tell tale mark just one things you pick up from the old guys in engineering look and listen to what they do and you learn things

like I said No one knows it all , your always learning never close your mind young or old there always some one knows more than you do, and learning is everything, yours anna j have fun

Previously kevin_wood wrote:

Thanks everyone.

I have worried all week and re-done the exhaust valves tonight with cutting paste. It has worked, but took along time.

I have only done this sort of thing once before, but on a more modern head.

I turned the head upside down and locked it in the vice. I filled the cups in the heads up thinners, not leaked a drop in an hour! Result!

Kevin,

Hate to spoil your party, so to speak, but lapping/grinding the valves should only take seconds to obtain a gas tight seal. That it took a long time would indicate too much eccentricity between the seat and guide. This is why accurate seat cutting is important as is minimum clearance between valve stem and guide. Kibblewhite recommend 0.0008"- 0.0012" inlet, and 0.0011"- 0.0015" exhaust when using their valves and guides.

The disadvantage of too much lapping is a pocketed valve, which reduces gas flow due to turbulence. Turbulence is good in the cylinder for complete combustion but not when it inhibits the volume flow rate of the air/fuel mixture entering into the combustion chamber, results in reduced power,

Regards,

Simon.

The valve seats on the YouTube video looked to be a long way down into the head. I've never seen them as deep as that. He did not comment. It looked similar to extreme valve seat recession and gas flow would be obstructed at small valve lift. I wonder - are designs like that common? It was a diesel engine so maybe just has a lot more heat to get rid of so the compromise is different?