Scored/scratched valves stems after lapping

[Fungus]

Hi,

I've just been lapping the valves into a cylinder head I'm building up. I was careful with the paste and I oiled the stems, yet they have still gone dull and gotten scratched following said process.



The lapped valve certainly doesn't slide into the guide as smoothly as the un-lapped, still-shiny one.

Should I worry about this? Would it be worth re-polishing them? Luckily I measured the stems with a micrometer beforehand, so i could always polish and then measure to make sure they're still in tolerance.

Cheers

[vitesseefi]

That paste has got in there I'm afraid. Easily done.

Polish up with fine wet 'n dry paper (1200 or finer) and gives the guides a really good wash out.

Nick

[skylinedave]

Should they not have had some sort of grey assembley stuff on them anyway for start up reasons ? Grapogen or something ? I may be barking up the wrong tree .

It does look like vitesse said , some thing has gotten in there , unless the head guides were not clean to begin with ......

[Fungus]

I'm a bit worried that the guides are gonna be ruined as they are softer than the valves.

I'm hoping that the engineering place that's gonna skim the head will be able to knurl the guides and ream them to size.

[Fungus]

Feb 13, 2015 22:51:39 GMT skylinedave said:

Should they not have had some sort of grey assembley stuff on them anyway for start up reasons ? Grapogen or something ? I may be barking up the wrong tree .

It does look like vitesse said , some thing has gotten in there , unless the head guides were not clean to begin with ......

The head is off the car, I'm lapping the valves in and getting it skimmed. It's not been run, the scratches are just from the lapping

[Deleted]

Problem is the valve guides are phosphor bronze. The valves stems being dull isn't an issue. The valve grinding paste now embedded in the guides is. Washing isn't going to get it out. If it's a motor you plan on keeping long term, change the guides. If it's a motor that's not destined for a long illustrious life, drive it as it is.

[Fungus]

Feb 14, 2015 6:21:43 GMT @johnnybravo said:

Problem is the valve guides are phosphor bronze. The valves stems being dull isn't an issue. The valve grinding paste now embedded in the guides is. Washing isn't going to get it out. If it's a motor you plan on keeping long term, change the guides. If it's a motor that's not destined for a long illustrious life, drive it as it is.

I phoned up the engineering place and they reckpn 'worst case' would be £65 for the valve guides so it's not the end of the world.

Would new guides mean lapping in the valves yet again?

[welshpug]

You'd need the seats cutting, done accurately there wont be any need to lap the valves in.

[Fungus]

Got it, thanks.

I was lapping the exhaust valves with course paste as they were pitted. I think I'll just use the current guides as sacrificial ones for lapping, that way I can get the valves all done and then it'll be ready for guides.

Thanks again

[composimmonite]

You lap valves AFTER fitting new guides - not before.

[dodgerover]

Does this engine run valve stem oil seals, if it does and you aren't going to be doing an immense annual mileage or pulling red line rpm's constantly I would just go with running what you have personally, worst case scenario is it blows a puff of smoke on cold start ups and uses a little more oil than it would have done, neither of which is the end of the world to me.

I can't get my head round doing the valves before getting new guides fitted, surely once the guides are fitted they will recut the seats using a cutter centred on the new guides?

Did you lap them using a sucker stick or a drill? Either way its easy to spread the grinding paste around if you aren't carefull, especially if you have the head upside down for easy access. You only need to use a tiny, tiny smear of it and a little parafin for lubrication

Edit sorry Mr Simmonite has faster fingers than me

[Fungus]

I lapped the valves using a stick. What I meant was, the exhaust valves are taking a lot of lapping due to more pitting than normal. I'm doing all the course lapping using the current guides, just to get the pitting off the valves.

Hopefully I can give all the valves a light lap using fine paste with the new guides installed. I didn't think there was any point sitting there spending 10 minutes on the exhaust valves with course paste and risk damaging the new guides. Might aswell get the worst off while the old guides are still in place, surely?

The engine does use stem seals on both inlet and exhaust valves, and will be a weekend toy. But since the engine is having new Pistons, rings, rebore, shells etc I don't really want to have valve guides that won't last.

Thanks for the helps everyone

[slater]

If they are fitting new guides id be dubious that the seats will be close enough to lap in afterwards. Usually the seats need cutting after you put new guides in. If they do that they should be able to use a 3 angle cutter and improve the flow too.

You can get the valves refaced for not too much as well. Its quite a quick job and you can put a back cut on them to help the ports flow (assuming your pepping it up a bit?)

I can understand your probably trying to save the cost of all that tho. If so id just bang it back together as is. If it goes tits up wont take much to take it back off and get it all done, i think the guides would likely be ok.

[Fungus]

Yeah I was thinking of having the valves back-cut/undercut the stems, and 3 angle seats would be a bonus.

Part of me says just stick it all back together, but the guides are pretty worn (1mm of valve deflection) and I want it to last.

[dodgerover]

Are you sure its not the valves that are worn? Valves are normally only cheap..

[Fungus]

Feb 14, 2015 20:07:49 GMT dodgerover said:

Are you sure its not the valves that are worn? Valves are normally only cheap..

Almost certain, I measured them all with a micrometer and most were bang on the brand-new spec, with a few being 0.008 under at the most.

The book says 1.3mm of side play/deflection is the maximum wear and they're on about 1.0, so it would point to the guides.

To be honest, as long as the scratches in the valves will polish out, I'll just do the guides and be done with it.

[Fungus]

Had a go at lapping in the remaining 4 valves just now, but this time i wrapped a few elastic bands just under the valve head.

It seems to have worked as far as stopping paste making it way down the stems and into the guide. There's still some scratching but nowhere near as much.

Tomorrow i'm gonna get some 1500 wet/dry and polish up the valve stems. I think i'll get a small pipe-cleaning brush and clean out the guides too. After that, if it all feels alright and there's not any more side-play, i'll just run it as-is.

Thanks for the help everyone.