Valve Stem Damaged

[newdean0 0]

I've taken apart the head on my mi and found this little beauty on one of the valve stems. It looks like there's some pitting on the stem though there's a definite line on it which makes me think it could be a manufacturing fault. The valve wasn't loose in it's guide so can I put this back in or will I need a new one? Can you buy single valves?

 

 

Also, I'm trying to get all the white caked-on crud off the back and face of the valve so I can grip it to lap in the seats, anyone know a good method to get this off? Wire wool and Silvo is a tad slow .

Edited February 27, 2006 by newdean0

[pug309twin40s 1]

hmm the pitting doesnt look good. Check condition of the inside of the valve guide. but i would get a new vavle and valve guide fitted

 

 

to clean the valve faces etc. stick the vavle into a drill then run the drill and rub some rough sandpaper on the valve gentle and all the dirt/crud will come off easily.

 

 

p.s.s that pitting shows there must have been some crap in the oil if it leaked passed the vavle stem seal?. I would take the sump off and check the condition of the bigend/main bearings

Edited February 28, 2006 by pug309twin40s

[PumaRacing 2]

hmm the pitting doesnt look good. Check condition of the inside of the valve guide. but i would get a new vavle and valve guide fitted

to clean the valve faces etc. stick the vavle into a drill then run the drill and rub some rough sandpaper on the valve gentle and all the dirt/crud will come off easily.

p.s.s that pitting shows there must have been some crap in the oil if it leaked passed the vavle stem seal?. I would take the sump off and check the condition of the bigend/main bearings

 

Nope. Thats a manufacturing fault. I'll hazard an opinion it's an exhaust valve and if you take a magnet you'll find the pitted part is magnetic and below that it isn't. That's because exhaust valves need 21/4N non magnetic steel to cope with the valve head temperature and magnetic EN52B steel at the top so that the collet grooves and tip can be heat treated. 21/4N can't be hardened. The two materials are friction welded together part way down the stem.

 

In this case a bar of faulty EN52B has been used and not spotted during manufacture. Actually it must surely have been spotted but no one gave a toss. However it hasn't broken yet and therefore probably never will but who would take the chance and put it back in an engine? The guide itself will be fine.

 

To clean valves spin them in a drill or lathe. Use a metal tool such as a chisel or lathe tool to remove the worst of the carbon from the head and neck of the valve and then 80 grit wet and dry to polish the remnants off. However don't touch the seat, stem or periphery with that. Use 400 grit on the lower part of the stem below the line where the valve runs in the guide and 1000 grit above that to lightly polish the chrome.

 

I once had a dipstick try to save a few quid on a head job by cleaning the valves himself. It's ok he says. I work in a toolroom and I can do them myself on the lathe. He used 80 grit on the whole valve and removed all the chrome from the stems in the process. He also smashed the tops off the valve guides trying to remove the stem seals with pliers. His economy measures cost him about 100 quid extra.

[newdean0 0]

Shonky french engine builders . At least a valve is reasonably cheap so I'm going to get another one. I guess this must be a Friday afternoon engine.

 

I could imagine it takes a fair bit of skill not to take chunks out of the valve using a lathe tool. I've been mucking around with stuff today and found a scrap bit of aluminium sheet does a good scraping job and most importantly isn't hard enough to damage the valve.