Fitting new valves and guides

[nevhunter]

You'll be unlikely to get remains of the abrasive out of the guide as it's relatively soft. The inlet "fit" can be quite close..001" is plenty The exhaust is another matter. .003" on a 3/8 guide is common. Try less at your own risk. Exactly parallel and a good finish is desired. Chrome or nitrided is best there on the stem to prevent galling. Nev.

[cmattina]

Thanks for everyone's comments.

It is funny, when i was doing it, I totally presumed it was not the correct way and a "brutish" (in Canada we would say "get 'er done") way of doing it, but I also considered that the bike had likely seen it all and is about the furthest thing from a 2020 BMW super bike - I don't think these bikes even have torque specs do they?

[nevhunter]

There would be some info somewhere or just use general figures for bolt/stud size. There'd be torque specs from the first nuts and bolts ever used. Back to the valve guides.... Getting the fit to the head is also critical. Guides come loose often in alloy heads on bikes. Less often with iron heads but the fit still has to be correct. How tight the removed one feels is a good indication for the size of the replacement. You must measure things and make sure the new ones aren't too tight a fit before you press or drive them in and damage something. Nev

[Simon.Gardiner]

They've got torque specs - but barely!

SG

[nevhunter]

If you are working all day long with spanners you get a good feel for correct tightness. There's still a lot of variability with dry and oiled threads etc and tension wrenches can be miles off and need to be checked regularly. SHORT studs that have no relief of the stem diameter concentrate all the stress near the thread near the unthreaded part. The weakest most stressed bit. Where expansion due temperature variation occurs these short studs don't do well. They stretch. It's poor design. It would work OK with Cast Iron but not so good when replaced with an aluminium part. A light even pre tension followed by a stipulated angle change on each nut would be a better approach. It's still difficult when retensioning where the gasket compresses. Nev

[john.whiting]

I once stripped one of the head studs in a D9H,using a 6ft long pipe extension ....didnt have a torque wrench read that high.......recently replaced the head gasket in a Ford 4 cyl diesel,and nearly pulled my shoulder out of its socket ,it needed so much force to turn the headbolts to the spec ...talk about tight ...and the bolts are only 10mm and 12 mm....Chinese bolts looked a bit dodgy too,but everything held,and its all good.

[john.bebb]

John W. - love the "6ft long pipe extension" to adjust the head studs - reminds me of using a scaffold pole as a lever to undo the drive sprocket on a Arrow several years back... and recently I sheared an 18" torque wrench whilst attempting to remove a wheel nut form my Ford Focus; - I'm ~ 66kg and was standing with both feet on the
end of the wrench & bouncing up & down... dunno what that comes to in foot pounds...
Whilst on the subject of torquing head studs - one has to laugh at the antics some will go to torquing a Mk1 Sq's head down correctly...
One requires a much modified (3/16 WW ring) spanner simply to gain purchase on the nuts under the inlet manifold & one can achieve bugger all rotation 'cos the fins &/or carb flange is in the way....
& as for getting them to the alleged "2lbf - ft" (!?!) - (Bruce Longman .doc Rev. Oct 2015)...
... well, that's another thread & story...
Cheers, John B.

[simon.holyfield]

Coming back to this old thread, I'm learning the hard way again. Cracking on home tonight on the W/NG, 55-60, she suddenly cut out. After finishing the ignition checks I kicked it over to find apparently no compression. I popped the exhaust valve cap off for a look, found nothing and a few minutes later she started OK and carried me home apparently fine.

Stuck valve? She was pretty hot, and I didn't ream the new exhaust valve guide 2500 miles ago when I rebuilt the engine. The valve was new too.

[Simon.Gardiner]

That used to happen to me when I'd set the exhaust tappet clearance slightly too tight....or when it got slightly too tight because the rocker box had sunk a bit on the gasket....
Might be worthwhile re-doing the tappet settings and then keeping an eye on things.
I've never had to ream a cast-iron valve guide and never had one show any signs of picking up. Where I have seen scoring on the valve stems it's been from engines that have been very severely abused (but I expect you're not in the habit of riding around with sand in the oil tank... )

SG

[simon.holyfield]

Spooky. How did you know that I had just replaced the aluminium rocker box gaskets with fibre ones?

I'll check the clearances. Thanks!