Machining valve pockets in pistons

This winter, I'm thinking a lot about what I want to do with my engine. Raising t he CR is fairly high up on the list, but at present I would prefer not to go the (sensible but somewhat pricy) JS lightweight piston and rod setup. I rather like the idea of using the 0.003" JS gaskets increase the CR, but this places the valves rather too close to the piston for my liking.

I do know that the head will require some attention, since at least one guide in a bit doubtful, the seats need some attention and the valves probably need replacing. The Norton PR notes have details on how to modify the standard pistons to put valve pockets in them, but I do not know of anyone locally who could be entrusted with this work, so my question is, who in the UK (or Europe for that matter) does Norton head work and can machine a set of pistons for me?

Mick Hemmings no longer has any Wiseco high compression pistons, not do Andover Norton seem to have any plans to stock them according to the reply I received from them.
Steve Maney seems to be rather busy doing his big valve conversions, but I'n not certain that I want to go down this path right now, and his high compression pistons seem to be rather heavy and expensive.

Any other suggestions?

What is the weight of the Maney high compression pistons?

What type of head gasket are you using at the moment?

Glen

worntorn said:

What is the weight of the Maney high compression pistons?

What type of head gasket are you using at the moment?

Glen

Click to expand...

I have a pair in my suitcase in the moment, but no scale. Back home late in the weekend...

I don't have a figure for the weight of the Maney pistons, but considering that they are made with a thicker crown than standard to allow for machining...

I have a standard composite head gasket at present.

Hi Steve, I would check on the postage to Pueblo Colorado and see about sending your head and pistons to Jim Comstock aka Comnoz here on the forum. You would know that they are in good hands, and could rest easy about it.

You can squeeze an extra half point of CR by using the thinnest of the composite gaskets, if you aren't already doing so.

Glen

SteveBorland said:

I don't have a figure for the weight of the Maney pistons, but considering that they are made with a thicker crown than standard to allow for machining...

I have a standard composite head gasket at present.

Click to expand...

I don't have the figures here in front of me but after you machine the .100 inch or so from the top of the Maney piston to make it streetable- it is around the weight of a stock piston. I have used quite a few of them that way without cutting the valve pockets. Of course that depends on the cam your using. Jim

Depends on whether you're talking 750 or 850. The Maney setup for a 750 actually weighs less than stock. A Maney 750 JE piston is not made with a significantly thicker crown, and complete with rings, pin, and circlips, weighs 326 grams. A stock Norton 750 piston (with the cutout in back of the oil ring in this particular case) weighs 338 grams in the same configuration.

For the 850s, it's a bit different. The JE pistons are made with a thicker crown to allow for machining to suit specific applications, and are heavier. An 850 piston in the same configuration as above weighs 395 grams. Unfortunately, I haven't weighed a stock one, so can't make the comparison. The JE piston has a deck height .150" taller than stock. If you machine .150" off the JE to get stock compression ratio, the weight, as Jim points out, will be much closer to stock. Cutting .150" off the top will reduce the weight by somewhere around 45 grams.

Ken

Steve,
If there is no one near you and if the US is too far away you could try SRM in Wales. They are well known for their quality work on BSA and are now branching out to other British makes. They did an 850 head for me last year, the work was superb and the price very competitive.

Dave

Doesn't Jim Schmidt supply 12 to 1 comp. pistons? If you don't intend to increase the upper limit of your operating rev range above 7000RPM surely piston weight would not be a problem if you use his light pistons ?

People were slicing pistons up to measure the thickness beneath the std valve cutaways many decades ago......but in those days pistons cost peanuts. Peter Lovell of Lovell Racing Developments In Burmingham I suspect has a jig for doing the job as he has been modifying Norton pistons for decades.

comnoz said:

SteveBorland said:

I don't have a figure for the weight of the Maney pistons, but considering that they are made with a thicker crown than standard to allow for machining...

I have a standard composite head gasket at present.

Click to expand...

I don't have the figures here in front of me but after you machine the .100 inch or so from the top of the Maney piston to make it streetable- it is around the weight of a stock piston. I have used quite a few of them that way without cutting the valve pockets. Of course that depends on the cam your using. Jim

Click to expand...

Thanks for the comments Jim. I'm using a PW3 cam, and when building the engine I tried checking piston - valve clearances with clay with no headgasket, thinking that if that was ok then there would be no problems using the JS 0.003 rings. I don't have my grubby bit of paper in front oof me, butthe results I saw (mostly with one valve as I recall) were such that I went to a standard gasket. Of course, I was pushed for time, and might have cocked up the measurements, but I did not see the 30 - 40 thou clearance I was hoping for - it was far less.

I have machined piston vale pockets on ac homemade Keats holder in a lathe using either a milling cutter or a flycutter- it is fairly easy but you need to know what you are doing.

Yeah, the pw3 will require pockets. Jim

SteveBorland said:

comnoz said:

SteveBorland said:

I don't have a figure for the weight of the Maney pistons, but considering that they are made with a thicker crown than standard to allow for machining...

I have a standard composite head gasket at present.

Click to expand...

I don't have the figures here in front of me but after you machine the .100 inch or so from the top of the Maney piston to make it streetable- it is around the weight of a stock piston. I have used quite a few of them that way without cutting the valve pockets. Of course that depends on the cam your using. Jim

Click to expand...

Thanks for the comments Jim. I'm using a PW3 cam, and when building the engine I tried checking piston - valve clearances with clay with no headgasket, thinking that if that was ok then there would be no problems using the JS 0.003 rings. I don't have my grubby bit of paper in front oof me, butthe results I saw (mostly with one valve as I recall) were such that I went to a standard gasket. Of course, I was pushed for time, and might have cocked up the measurements, but I did not see the 30 - 40 thou clearance I was hoping for - it was far less.

Click to expand...

Burt Munro's simple but effective piston holding fixtures for cutting valve pockets in pistons

An old dodge used to be to cut teeth into an old valve, assembly in situ without springs etc. put the end of the valve in a drill, and merrily cut into the piston. Measure. Repeat. Carefully.

Sounds crude I know, but it works, I've done it before.

Its easier these days to get a mate with a mill to do it. IF you have a mate with a mill that is...

for my 750 i used maney pistons, of wich i took 1mm off the crown , as i had already shaved the head previously.
their weight 249gr + 63.5 for the gudgeonpin
i very strongly advise against the wisecos,lovely pistons as they are , but they have no provision for squish
i keep 2mm space between piston and valva on full lift, squish 0.8 mm
i did not have to machine the pistoncrowns but have done in the past

how to cut ? measure what gap you have , and than see what you want(i go for 2mm )
use a scap valve in wich you cut a slice out off the part that you see when the valve is closed , looking in the combustionchamber.
take a scrap piece of round bar,drill a hole the dia of the valvestem and fix the scrapbit onto the valvestem ; after you fitted the valve in the head
you have to drill and tap a second hole to fix the scrapbit securely to the valve stem
put a drill or rotary machine on the valvestem and push and pull
now you have a valve pocket cutter

i realize my explenation is not very clear but it works

ps imho more than 10.5 to 1 is not efective on a std commando ,just adds problems, and yes my roadbike had more , thats why i machined the pistoncrowns
better to set everything up right , like valvespringpressure etc

hoi fast freddie; had the same thoughts at the same

Fast Eddie said:

An old dodge used to be to cut teeth into an old valve, assembly in situ without springs etc. put the end of the valve in a drill, and merrily cut into the piston. Measure. Repeat. Carefully.

Sounds crude I know, but it works, I've done it before.

Its easier these days to get a mate with a mill to do it. IF you have a mate with a mill that is...

Click to expand...

lynxnsu said:

hoi fast freddie; had the same thoughts at the same

Click to expand...

+1

I found this on Google:
http://www.fordmuscleforums.com/engine- ... ching.html

looks like an interesting method.