FWIW I use theNeway kit and cut 3 angle seats on just about everything
On a SV engine, it is no where nears as important to be precise ( although it won't hurt ) as you have to be on an OHV engine
I have seen SV's with near 0.010" clearance on the guides that run quite well.
As for lapping as MArk said, the 1 deg out cut works fine without lapping but I use a std cutter so still lap but it is very minimal ond only done with extra fine paster
The Neway people claim if you sut the seat and also the vlave on their gear there is no need for lapping .
Down side is a kit will cost you way more than geting it done and once it gets out that you have one then you will suddenly find you have a lot of friends .
Most of the probles with Neway kits is peoplepush down to hard and turn too fast, they are hand tools not machine tools and then when the carbide insets are worn they just press harder
As previously mentioned , get the adjustable guide
It is not as accurate as the single size guide but again it is only a low compression side valve engine
Whatever you do, do not buy one of the kits sold on ebay / amazon out of India
I have correcte a lot of seats that those kits made a big mess of .
It's also worth noting that if the valves are 'pocketed' into the top face of the barrel it's best to consider having the seats replaced...Pocketed valves reduce gas flow and the M20 has little enough performance as standard without squandering any.....
The hardened seat will also considerably extend the service intervals on the exhaust side...I have plenty of personal and anecdotal evidence that these engines will run fine on lead free with standard seats for local work or limited duration runs but personally, I found that long motorway runs at cruising speeds led to seat/valve problems far more quickly so I've been replacing the exhaust seats as a matter of course for decades...Ian
0.003” should be fine. Don’t go any tighter or the seat could close in on itself. With an iron head/barrel the seat should grow with the head at a similar rate. Just make sure you have a very clean finish on the bore for the seat.
What seats are you planning on using? The AE 6000 series are supposed to be good. Fondera sell the Martin Wells seats, but they can be tough to cut. They did say the last time I visited that they also have a range of seats better suited to cutting rather than grinding.
I was thinking of using powered metal seats from Kibblewhite here in the USA. I normally use nickle chrome seats and have heard the powered metal seats can't be cut and need to be ground. I have also been told you can cut them so I don't know who to trust. Luckily I have a seat grinder if they can't be cut.
