[mhynze]

Hi, so tried the upside down leak test on valves.. One side is good, one side has a very slow leak..... Have people had success with lapping?

 

[76TWIN]

Yes I lapped mine when I rebuilt the top end. Been working fine.

 

[Lefty]

There's probably a few hp to gain from a perfect valve job. Most of us are probably running around on less and it'll work.

 

[mhynze]

So i first read about the acetone test on here... and forgive my stupidity, is it done with the valves simply sitting in the head? or with the seals and torsionbars installed too ? I cleaned up the valves a bit more and after 20 minutes it leaked about 1/4 of the diesel out but this was with the valves just sitting in the head by themselves ... a few hours later they were completely drained. I'm going to get some Easy off and clean out the exhaust ports tomorrow, but with that kind of leakage over 20 minutes with the valves just sitting it would you reckon they are pretty good then? Just lap them for good measure?

*note the second picture has a bit of an optical illusion making the back half look like its a lower level

 

[Simo]

I used acetone, with valve Springs in place (its a cb175) by pouring the acetone in the intake ports, then flipping the head and filling the exhaust ports and looking for leaks into the combustion chamber, that way you can tell which valve needs attention.

 

[pikl]

I normally fill up the port with standard fuel. The valves need springs to seal, although just pushing them in with a hand may also be enough if they are lapped well. If they are bad, they start to leak almost instantly. If I do not see any signs of fuel in the combustion chamber after some 30 seconds, it was always good enough for me (in this case, it probably evaporates faster than it leaks). On most bikes, especially if they were not running for a while, the fuel will just flow through the closed valve like nothing.
I think the bigger the valves are, the harder it is to seal them (need stronger springs). The valve seat angle is very important as well. The beauty of Ducatis desmodromics is that (apart from high rpm capabilities) there is almost no resistance when you turn the crankshaft (no actual valve springs), so far less losses there...

 

[Lefty]

If you hold a straight edge to the seat surface if front of a light you'll probably notice it's worn concave. When the valve closes it doesn't land on the seat and is dragged in place causing wear. If your guides aren't too worn maybe new valves and the minimal cut on the seats would give good service. If you want cheap maybe look into having the valves refaced. Depends how thick the stellite is, I think they put a pretty good layer on there. New guides can open a can of worms. The concave worn seat is probably how most of em running are out there. Someone needs to have a batch of valves with a true 7mm stem made. Harley's have 7mm stems. That would make a valve job way easier.

 

[tbpmusic]

......Someone needs to have a batch of valves with a true 7mm stem made. Harley's have 7mm stems. That would make a valve job way easier.

I did have a batch of super-high quality stainless valves for 450's made by Ferara - no one here bought them. I sat on them for over three years.
Most of the people here are not willing to pay for quality, I discovered.
Pay $20 for a valve, a $20 valve is what you get.
Pay $60 per valve and you can get stockers (ugh), or you could have gotten some of mine.
Too late now, they're gone........I did put a set in my rider, along with brand new valve seats (not re-cut, NEW).
Shown here compared to stockers - though there is no comparison really......

 

[Lefty]

I did have a batch of super-high quality stainless valves for 450's made by Ferara - no one here bought them. I sat on them for over three years.
Most of the people here are not willing to pay for quality, I discovered.
Pay $20 for a valve, a $20 valve is what you get.
Pay $60 per valve and you can get stockers (ugh), or you could have gotten some of mine.
Too late now, they're gone........I did put a set in my rider, along with brand new valve seats (not re-cut, NEW).
Shown here compared to stockers - though there is no comparison really......

Bill- were the stems a true 7mm or sized under to use a 7mm reamer on the guides like the stockers? My point being a 7mm stem would allow the existing guides to be renewed back to spec. It's too much to ask for a new guide to land a valve exactly on the old seat. It would hopefully save you from having to fit NEW seats.