Hi All
Can anyone recommend a valve seat cutter and guide for the M20 please, I have a barrel with some pitting in the seat and would be best to re-cut but sending to the UK to have it done from Guernsey is getting a bit expensive now with shipping and customs in the UK
Regards
Carl
email (option): edgeprotectionsystems@gmail.com
Plenty of kits on ebay Carl.
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l2632&_nkw=motorcycle+valve+seat+cutter&_sacat=34998
Ron
email (option): ronpier@talk21.com
At least afterwards the barrel can be saved by fitting valve seat inserts.
email (option): pes.sales@btconnect.com
In principle valve seat cutters can be used with care if no machinery is available, back in the day it was common practice before the arrival of Serdi head machines etc...
The problem with the M20 is the pilot for the cutter...Due to the 'bastard' size of the M20 valve stem something will have to be made/modified to give a good fit...This is obviously key to getting the seats cut true to the guide...
Stem size is .3475"-.3485" for both the inlet and the exhaust valves...When everything is new the valve guide clearance should be .003"-.005"....I usually finish the inlet guide to the smaller size after fitting and the exhaust nearer to the upper end....
Of course, old guides will be worn to an indeterminate degree...It is therefore plain to see the problem of achieving a good fit for the pilot into both guides, particularly if the engine has done a lot of work but even with new components...Ian
email (option): ian@wright52.plus.com
You don't need to make or modify a pilot to fit the odd M20 valve guide size (.3475 to .3485").
What you need is an adjustable 11/32" pilot which has a range of .340" to '360" or an adjustable 8.5mm pilot which has a range of .332" to .352".
The adjustable pilots are not cheap, costing about $45 each.
That how I do the valve seats on my M21.
i spook to some very nice people at Fondera UK who bring in the Neway cutters, Richard there very helpful and sorted the cutter and pilot i need
well recommend them if anyone looking for cutters
Regards
Carl
email (option): edgeprotectionsystems@gmail.com
['The adjustable pilots are not cheap, costing about $45 each...']
Well you learn something every day, I've never come across those...The Serdi machines, which is how mine get done these days, have an extensive set of pilots that go up in small increments to suit just about anything...Ian
email (option): ian@wright52.plus.com
The neway cutters date back before the 60's. When new they cut quite well, but doesn't take long before they are blunt.
The seat formed isn't good enough to make a seal and will need lapping.
In the early 70's major manufactures stopped lapping valves and used an interference angle on the seat. 46deg on the seat and 45deg. on the valve for example. With improved seat cutting the interference angle sealed almost immediately and soon hammered down to cover the seat width.
The valve seat now consisting of three cut angles.
Machines like the serdi's all suffer from a massive weight over the guide/pilot. This can influence the concentricity of the seat.
Though they are very quick and easy to use.
I invested in a Swiss system that measured the bore of the valve guide and stopped in the calculated centre. At this time cosworth were still cutting seats with a milling machine.
Although the most accurate system made, it proved to fragile for the average engine jobbing shop. It doesn't take much to break it. :(
The seats are cut using form tools with the three angles on them specified by the engine manufacturer. For competition use they produce forms with blend angles in and out of the seat.
There is now a stupidly expensive machine that serdi bought the rights too that uses a "U"axis and a single point cutter to form any seat profile you can imagine. Still I think it suffers from the problem of weight over the pilot. Even this technology is about thirty years old.
Don't get me wrong, these machines are so much better than anything you could do by hand.
If you want to be sad and look up the many forms of valve seat cutting you'd be shocked.
I initially trained as an engine remanufacture then moving on to a cylinder head development engineer. I've used most systems over the years.
Remember lapping valve damages the working face of the valve. It must be perfectly flat.
Mark
email (option): pes.sales@btconnect.com
A servicable job at a reasonable price is generally what most owners of old bikes aspire to...The exceptions are those involved in competition and anyone with an enquiring mind and an accuracy fetish..:laughing: . It seems it is increasingly the case that people don't always have a 'local' engine shop to help out/rely on anymore and are prepared to have a go using the 'old' methods, which can frequently be carried out in a reasonable home workshop to a standard that is certainly functional....Ian
email (option): ian@wright52.plus.com
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
email (option): ian@wright52.plus.com
For those who have replaced the valve seats on a M20, what shrink fit are you using? I was thinking .003" would be OK?
I have replaced valve seats on various bikes but not on a M20 yet and the M20 runs really hot at the exhaust port so .005" may be better?
I have a M20 cylinder that needs new seats and will be doing it on a Bridgeport mill.
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.
Mark
email (option): pes.sales@btconnect.com
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.