hi can anyone tell me what valve seat cutter is needed to re seat my m21 barrel valve as its pitted , and is there a maximum you can go, also the d/s shim do i need them as both cranks that i stripped down didnt seem to have them and how do i determine if they are needed.

email (option): markbrob1@hotmail.com

Hi Mark..Both valve seats are cut at a 45 degree angle. Seats should be cut as lightly as possible to clean up. The absolute max. the seats should be cut before fitting a new seat is till the top of the valve is level with the gasket face.
On the drive side you have the spacer between the main bearings..this should measure 1.000"-1.005". If it is within these dimensions no other shims are required. Also make sure the oil flinger is flat and unworn where it sits against the flywheel face...Ian

email (option): ian@wright52.plus.com

Just for comparison I’ve checked a N.O.S. inlet valve in a N.O.S. barrel. The valve head sits about 0.050 inches above the face of the barrel and the valve seat in the barrel (not easy to measure accurately) is 0.060-0.080 inches wide – probably a nominal 1/16”. The exhaust valve seat doesn’t appear to be any wider although contemporary wisdom suggests it should be about 50% more in order to shed heat more easily.

ChrisJ

You're right Chris..1/16" is definitely on the narrow side for the exhaust seat...The exhaust valve (which runs red at operating temperatures) needs to lose heat through both the seat and the valve guide, but the greater part is transmitted via the seat...Ian

email (option): ian@wright52.plus.com

thanks for that fellas

email (option): markbrob1@hotmail.com

so can you tell me what size valve cutter i need

email (option): markbrob1@hotmail.com

Hi Mark..Diameter of the inlet valve head is 1.737", diameter of the exhaust valve head is 1.612". The problem though, will be sourcing a suitable mandrel to fit the valve guides snugly as these are a non standard size. The valve stems are .3475"-.3485" and there should be a .003"-.005" guide clearance...
This would give a lower bore size for the guide of .3505" and an upper size of .3535" depending on stem size when new and current amounts of wear.
You will need to measure the guides to determine the size you have in each one and what you need to find (or make) to use as a mandrel to centralise the seat cutter....Ian

email (option): ian@wright52.plus.com

Hi, it dosen't really matter what size cutter you use as long as it isn't that big that it misses the seat! As long as it is a similar size it will do the job they are really only available in different sizes just so that you don't catch the head gasket face if it were too big. Multi tooth cutters are really only useful if you want to use them on soft seats, if you want one that you can use on other vehicles with hardened seats you will need to use a tipped cutter or a grinder type, both of which tend to be pretty expensive and unjustifiable for DIY use. I don't want to push the one I have for sale, but it is a pretty cheap secondhand tool (that was expensive in it's day) that you can expand upon that would probably be ideal for the job and a lot better bet than a pre sized model specific one that you can only use on one specific size of valve seat. I only have the cheap one for sale (£50) at the moment, it is in the parts for sale section. As Ian says, usually they only need a very light cutting/grinding, people tend to get a bit carried away doing them! If you take them to a car engine rebuilders they would probably only charge about £20 to do them for you.

email (option): davmax@ntlworld.com