Valve Margin

[Brilig]

Hello Everyone,
I'm rebuilding my 1979 1000SP and I am looking for the Valve Margin specification.  I'm lapping the valve seats and have a little more to go to get the last of the pits out of the exhaust valves.  The Margin is down to about .045  .  Too small?
Thanks,
Mark

[Rough Edge racing]

 I am not a  Guzzi expert but on other air cooled two valve heads you should see .090 minimum. How wide are the valve seats you are lapping?

[oldbike54]

 It will run really hot with that small of a margin .

 Dusty

[usedtobefast]

Does this manual have the details? https://www.thisoldtractor.com/mg_manuals/workshop_manual_1000-sp-iii_en.pdf

[lucky phil]

Hello Everyone,
I'm rebuilding my 1979 1000SP and I am looking for the Valve Margin specification.  I'm lapping the valve seats and have a little more to go to get the last of the pits out of the exhaust valves.  The Margin is down to about .045  .  Too small?
Thanks,
Mark

If the seats are pitted you need to cut them first before you lap them. Lapping is just the final action to get them the last 2 or 3 percent of perfect, like using a steel on a knife blade to keep the honed edge on a properly sharpened knife it's not for taking out significant defects/damage.

Ciao

[Brilig]

Thanks for the information.
The intake and exhaust valve seats in the heads are about .080 wide and look to be in very good shape with no pitting.  The intake valves look to be in good shape too.  Just the exhaust valves appear to be beyond saving.  Do you think I could get away with just dropping in a new set of exhaust valves?
I'm planning on doing a more extensive restoration in the future but would like to get the bike on the road for a little while before I do that.
Thanks for the help.  This is my first rebuild so it's a learning experience.

[Don G]

Valve seats should be about .045" in width, in reality you should just bite the bullet and have a professional examine the guides and seats as well as the valves. If not, bang it back together and hope for the best.  DonG

[John A]

Valve seats should be about .045" in width, in reality you should just bite the bullet and have a professional examine the guides and seats as well as the valves. If not, bang it back together and hope for the best.  DonG

It pays to have the “right” guy ,  some of the speed shops for automotive don’t have small enough stones. Shops for small air cooled engines are better generally .

[dxhall]

Any suggestions on who the “right” guy would be?  I’ve got a set of heads from a convert motor I’d like to have redone.

[Rough Edge racing]

  Older design hemi chambers do better with a wider exhaust seat, about .090..The very hot exhaust valve's primary cooling is the micro second it's seated...The wider seat helps cool the valve and lessen the possibility of detonation or pre ignition...

[John A]

Any suggestions on who the “right” guy would be?  I’ve got a set of heads from a convert motor I’d like to have redone.

Sadly I do not,  the ones I liked have retired. It’s another aspect of getting old I guess- everybody I know retires or croaks when they have acquired  a lifetime of knowledge and experience .  If there is no one local to you, I’d try Charlie at Antietam cycle. There’s others but my brain needs coffee

[Rough Edge racing]

Any suggestions on who the “right” guy would be?  I’ve got a set of heads from a convert motor I’d like to have redone.

  Where do you live? Do you want to ship the heads? Do you want first class valve work?

[dxhall]

Denver.  Shipping is fine.  I could do an average job on them myself, but don’t have the equipment to do a great job.  Having said that, though, I know that it’s the skill and care of the operator that makes the difference, and not just whether he has a shop full of Sunnen machines.

[usedtobefast]

I was going to send my heads to Harpers ... figured they know what they are doing and have all the parts handy.

But I checked around locally and found an excellent shop that focuses on BMW airhead models (motorcycles) ... the worked needed is very similar so I am using them to get my Quota heads sorted out.   One shop was BMW only so they declined the work, but another shop had done a few Guzzis, and Nortons, etc. 

[Rough Edge racing]

Denver.  Shipping is fine.  I could do an average job on them myself, but don’t have the equipment to do a great job.  Having said that, though, I know that it’s the skill and care of the operator that makes the difference, and not just whether he has a shop full of Sunnen machines.

   State of the art valve work is now done on single axis machines like a Newen, or the older Serdi. There are guys with hand held equipment doing good jobs however.
 All the the valve I have had done was at auto machine shops except for my vintage race Triumphs. I can recomend Rob Hall at Hall's Custom Vintage in NC..
  I know there are good shops in the Denver area, youjust need to find them

[RinkRat II]

   The one major caveat is to not let them talk you into the new Hi-perfomance air cooled valves!!!

                                     



      Paul B

[Brilig]

  Older design hemi chambers do better with a wider exhaust seat, about .090..The very hot exhaust valve's primary cooling is the micro second it's seated...The wider seat helps cool the valve and lessen the possibility of detonation or pre ignition...

This sounds right as the original seats are about that wide.
I think I'm just going to drop in two new exhaust valves, lapp them to get a good seat, and ride this thing for a bit while I decide what I want to do with it when I do a real rebuild.  I butchered it pretty bad when I was in my 20's  so it's never going to be an SP again.
The iron cylinder bores are nearing the outer limit of being in spec as are the main bearings and crank bearings.
I mostly just don't want to do anything that would cause damage.
Thanks to all for the good information.

[moto-uno]

  If you're installing new valves , then rather than lap them ( that's really old world tech today) check them with Prussian blue and leave their
perfect seats alone , (if possible) . Or continue lapping the old valves until you're satisfied and install and ride for a summer until you have the money to do
the complete job , with new stuff . Unless you're planning on a number of cross country trips , it'll be okay ( and fun ) for a summer . Peter
(not so quick to let others spend my money)