Valve grinding paste

[wookie]

Hi

I've re-cut the valve seats on my motorbike and now need to finish them off by grinding them in.

Any preferences for the grinding paste to use ?

thanks as always.

 

[chris pruteanu]

Ihave used cheap one from halfords before, the one box with 2 type of paste in one box... I think it was made by Laser. Their grinding sticks are rubbish but the paste is ok!

 

[frank horton]

most grinding stick rubber suckers are to thick.......I spin mine down a bit on the side of the bench grinder.....making the sucker walls thinner......works for me......

 

[wookie]

I can't use a sucker on the exhaust valve as the face of it is pitted but as both valves have a slot in the face I was just going to use a big flat screwdriver instead, or will that not work ?

Sorry for all the questions but I've not done this before.

 

[msmbus2000]

put a bit of rubber hose on stem of valve and pull backwards while other end is in a cordless drill

 

[anto44]

It's not the quality of the paste that's important, it's the quality of the apprentice that you lumber with the job of grinding them in

 

[brightspark]

put a bit of rubber hose on stem of valve and pull backwards while other end is in a cordless drill

yep that's what I do works a treat put a jubilee clip on it though

 

[wookie]

It's not the quality of the paste that's important, it's the quality of the apprentice that you lumber with the job of grinding them in

Well that's gonna be yours truly and I'm defiantly a novice (at best) so any and all advise very gratefully received, thankfully it's a single cylinder engine so only 2 valves to do. Mind you I have a Rover V8 that also needs doing at some point in the future so I'll have plenty of time to improve.

 

[wristpin]

Presume if you’ve recut the seats you’ve refaced the valves as well so only use the fine paste . Not a fan of spinning valves with a drill, when I was learning it was a “ hanging offence” ! Put a light spring under the valve head so that it lifts the valve off the seat. Twizzle it back and forth, allow it to lift , quarter of a turn and twizzle again and so on. That way you don’t get tramlines round the valve and seat. Proper job.

 

[anto44]

Presume if you’ve recut the seats you’ve refaced the valves as well so only use the fine paste . Not a fan of spinning valves with a drill, when I was learning it was a “ hanging offence” ! Put a light spring under the valve head so that it lifts the valve off the seat. Twizzle it back and forth, allow it to lift , quarter of a turn and twizzle again and so on. That way you don’t get tramlines round the valve and seat. Proper job.

Yep that's the way I was thaught to do it too. Proper valve lapping machines work like that also.

 

[8ob]

An old boy I worked with argued that paste was a waste of time, he reckoned the paste held the valve higher on the seat and the second the paste was not in there the valve dropped down onto an unground surface. He reckoned stone the valve and seat to the correct angle and fit/forget. I still lap valves but when doing it his words echo in my empty head

Bob

 

[RichardM]

Presume if you’ve recut the seats you’ve refaced the valves as well so only use the fine paste . Not a fan of spinning valves with a drill, when I was learning it was a “ hanging offence” ! Put a light spring under the valve head so that it lifts the valve off the seat. Twizzle it back and forth, allow it to lift , quarter of a turn and twizzle again and so on. That way you don’t get tramlines round the valve and seat. Proper job.

As above, also check the width of ground surface, you may have a spec for it, I go for 1mm when grinding in bike valves

 

[wristpin]

An old boy I worked with argued that paste was a waste of time, he reckoned the paste held the valve higher on the seat and the second the paste was not in there the valve dropped down onto an unground surface. He reckoned stone the valve and seat to the correct angle and fit/forget. I still lap valves but when doing it his words echo in my empty head

Bob

That's an interesting theory but not sure about its validity.
I always face the valves and skim the seats even if just enough to show that they are true. Then lap with thinned down fine paste. Grinding away with the coarse paste rather than facing and cutting was yet another "hanging offence"!

Useful lapping tool with pneumatic action.

https://www.buyamower.co.uk/product/briggs-stratton-valve-lapping-tool-19258.aspx

 

[brightspark]

if the seat and valve have been cut or ground it will take very little effort with fine paste and leave a dull grey finish when completed

 

[Rig Pig]

I like to test for leakage after I've lapped valves in, clean everything up install the valve and tip a drop of wd40 or paraffin into the combustion chamber and leave it to sit for 10 minutes or so.

 

[8ob]

That's an interesting theory but not sure about its validity.

He worked at the RAE Farnborough as a mechanic building aircraft piston engines so should have known his stuff, he also went on to say they dont lap valves in on new engines either so I suppose he has a point. If all the angles and machining are correct its unnecessary. But I still do it

Bob

 

[wristpin]

He worked at the RAE Farnborough as a mechanic building aircraft piston engines so should have known his stuff, he also went on to say they dont lap valves in on new engines either so I suppose he has a point. If all the angles and machining are correct its unnecessary. But I still do it

Bob

He’s right about the no lapping of new engines. Whether all new ones , I don’t know, but certainly Briggs and Stratton don’t . Another interesting thing that came to light re Briggs was the setting of valve clearances on side valve engines . Guess that they are robot assembled now but when hand assembled the op had a rack of valves with fractionally different length stems and selected ones that gave the right clearance. In service we have to grind the end of the stems to restore clearance - rather crude!

 

[whm_fab]

Presume if you’ve recut the seats you’ve refaced the valves as well so only use the fine paste . Not a fan of spinning valves with a drill, when I was learning it was a “ hanging offence” ! Put a light spring under the valve head so that it lifts the valve off the seat. Twizzle it back and forth, allow it to lift , quarter of a turn and twizzle again and so on. That way you don’t get tramlines round the valve and seat. Proper job.

+1, you will get tram lining doing it with a drill.
the only way, is to get those palms raw red with a sucker stick - back forward in palms for >5seconds, lift, repeat

 

[slim_boy_fat]

But I still do it

Old habits die hard.

 

[gaz_moose]

I take the rubber sucker off the wooden stick and put it on the end of my 3/8th speed brace. saves my hands getting battered.

I use the paste that comes In the double sided tin, has 'Tesco value' stripes and an orange or red logo