valve seat cutting, specs ? interference method ?

[PatAllen]

Who here used interference angles on a M10 ? like cutting 46 deg. on the seat and using 45 deg on the valve ?

this is known to promote better sealing and some flow improvements...

what are the spec (from blue book ?) about the angles ?

thanks.

[roadhog0]

Here is what my spec sheet says.

[PatAllen]

thanks for the details.

i found out from the blue book from the 2002 and e21

45 deg seat angle

15 deg outer correction angle

1.5-2.1mm seat width

surprisingly, there was no lower correction angle specification in neither of the blue book (60 or 70), so i assume it was a 2 angle valve job back then.

i confirm that all the "stock" heads i have (i checked on 5 among many others) only show a huge 45 deg seat and barely an upper 15 deg angle. most of them have huge aluminium protrusion around the seat, like f the seat itself was pushed too far in the head...bad for air flow.

[roadhog0]

thanks for the details.

i found out from the blue book from the 2002 and e21

45 deg seat angle

15 deg outer correction angle

1.5-2.1mm seat width

surprisingly, there was no lower correction angle specification in neither of the blue book (60 or 70), so i assume it was a 2 angle valve job back then.

i confirm that all the "stock" heads i have (i checked on 5 among many others) only show a huge 45 deg seat and barely an upper 15 deg angle. most of them have huge aluminium protrusion around the seat, like f the seat itself was pushed too far in the head...bad for air flow.

Well thats sorta odd... Yah, all I had done was a 2 angle on my head earlier this year and it works fine!

[PatAllen]

thanks for the details.

i found out from the blue book from the 2002 and e21

45 deg seat angle

15 deg outer correction angle

1.5-2.1mm seat width

surprisingly, there was no lower correction angle specification in neither of the blue book (60 or 70), so i assume it was a 2 angle valve job back then.

i confirm that all the "stock" heads i have (i checked on 5 among many others) only show a huge 45 deg seat and barely an upper 15 deg angle. most of them have huge aluminium protrusion around the seat, like f the seat itself was pushed too far in the head...bad for air flow.

Well thats sorta odd... Yah, all I had done was a 2 angle on my head earlier this year and it works fine!

well, dont get me wrong, the "prescribed" 2 angle is good enough, 3 angles is just better, but everything is relative there...it is meant to breaks the first sharp angle and should makes better flow. On BMW 4 cyl i think 3 angles appeared on the M42.

I am about to buy a set of Neway grinding stones to grind the seats myself, and will quantify exactly on my flow bench what kind of "improvement" it makes.

[aa/fd]

Pat, you might want to explore some seat angles other than 45 on your new flow bench. The results can be surprising.

[PatAllen]

Pat, you might want to explore some seat angles other than 45 on your new flow bench. The results can be surprising.

yeah i know, i saw 40 deg. have been used sometime, i just dont have a valve grinder so i cannot change angle that easy on the valves...i dont want to spend 25 years either in r&d, while everything has been done already...

i just want to try what is known to work and see result..

15-45-60 deg. reseat

30 deg. back cut on the valves

and some carefull intelligent flow tested porting

[TobyB]

funny- I've been looking at neway stuff, too. The valves I can grind with a

toolpost grinder on the lathe.

But damn, it is not cheap...

I had an M20b25 apart a while back and it looks like they used the

45/45.5 numbers, at least on the intake. The exhausts were too

well seated to tell.

t

[PatAllen]

i just bought a Neway "gizmo" valve cutter from e-bay...not the seat cutter but the valve cutter...30 deg. and 45 deg.

maybe i should start to offer cylinder head service...lol...