What's the best way to check cylinder head valves for leakage? - Page 2 - PeachParts Mercedes-Benz Forum

lietuviai · #16 06-25-2007, 10:55 PM

I found a bunch of oil had leaked through almost all of the valves. Is it possible for so many valve to leak if the engines had run at one time before their disassembly?

t walgamuth · #17 06-26-2007, 05:29 AM

The head is off, just have a valve job done. The r and r is the biggest expense on a valve job anyway.

Tom W

Stevo · #18 06-26-2007, 10:54 AM

Can anyone tell me what would be wrong with lapping the valves on a 616. Lets say there is no slop in the guides, valves are not burnt and your going too use this head when you reassemble the engine. Why not lap the valves?

larry perkins · #19 06-26-2007, 05:22 PM

steve if you look at a cross section of the valve seat and the valve sealing surface after lapping with grinding compound you will see that both surfaces develop a concaved form. if that is what you want go for it. most specs call for a .5 degree difference in the flat surfaces and the only way i can get the surfaces flat and at the correct angle it to grind the surfaces.
larry perkins lou ky

Stevo · #20 06-26-2007, 09:22 PM

Quote:

Originally Posted by larry perkins

steve if you look at a cross section of the valve seat and the valve sealing surface after lapping with grinding compound you will see that both surfaces develop a concaved form. if that is what you want go for it. most specs call for a .5 degree difference in the flat surfaces and the only way i can get the surfaces flat and at the correct angle it to grind the surfaces.
larry perkins lou ky

Ah, I see, that would go for valve lapping in general then. Thanks for the reply. There are allot of folks, including you maybe, around here that come from a background of "wrenching" then there are allot that didnt do much, except basic maintence, like me (I would change out a starter or minor tune up, thats about it

) , till I got one of these fine old MBs....."Valve lapping" is not a good thing on any engine it sounds like.

lietuviai · #21 06-26-2007, 11:22 PM

Quote:

Originally Posted by t walgamuth

The head is off, just have a valve job done. The r and r is the biggest expense on a valve job anyway.

Tom W

There was a forum member who I think spent over $1000 on rebuilding a head. There's no way I would dump that kind of money on a car that cost only $200.

t walgamuth · #22 06-27-2007, 03:59 AM

Well, he spent money doing a lot more than grinding the valves.

If $200 is your limit you may as well never tear a head off since I bet the gasket set alone is more than that.

Tom W

t walgamuth · #23 06-27-2007, 04:01 AM

Quote:

Originally Posted by larry perkins

steve if you look at a cross section of the valve seat and the valve sealing surface after lapping with grinding compound you will see that both surfaces develop a concaved form. if that is what you want go for it. most specs call for a .5 degree difference in the flat surfaces and the only way i can get the surfaces flat and at the correct angle it to grind the surfaces.
larry perkins lou ky

In looking back over thirty years.....I bet this is why my valve replacement on my 62 190c finney only lasted 30,000 miles. I just installed the valve and had a machinist lap it in for me. I did a head r and r all in one saturday on that car!

Tom W

lietuviai · #24 06-27-2007, 09:47 PM

Quote:

Originally Posted by t walgamuth

Well, he spent money doing a lot more than grinding the valves.

If $200 is your limit you may as well never tear a head off since I bet the gasket set alone is more than that.

Tom W

$200 is not my limit but I have to set some sort of limit in general, otherwise I'm better off buying a running example.
I have a full gasket set from top to bottom already. I only paid $109 for everything.
I'm going to call around to see where I can get the best price just to grind the valves and seats.

WINGAS · #25 06-27-2007, 09:52 PM

Lapping is to ensure that the seating surface are good all around AFTER the valves and seats are ground separately! I'd just have the seats and valves reground, i.e.,, have a valve job done. There is NO WAY they are sealing all that well anyway. You're making the right call.

lietuviai · #26 06-27-2007, 11:35 PM

Then I have to decide whether I'm going to put in new rings. The cylinder bores still seem to have some crosshatching left.

Shorebilly · #27 06-28-2007, 07:52 AM

Many moons ago, when I was in High School I worked in a "Full Service" Gas Station.....this was my second "real job".....one of the mechanics there showed me this little trick.....I was intending to purchase a '58 Chevy Impala with the 348 Tri-Power option.....he held a piece of note paper up against the end of the exhaust pipes.....if the exhaust keeps pushing the paper away from the pipe the valves are good......if the paper flutters (gets sucked back to the pipe) the valves are bad......I have used this method when evaluating used cars many times......obviously it is only a rough indication of the condition of the exhaust valves, but does give an indication if something is amiss in the head (valves burned or out of adjustment).....

SB

Shorebilly · #28 06-28-2007, 08:14 AM

Quote:

Originally Posted by Stevo

Can anyone tell me what would be wrong with lapping the valves on a 616. Lets say there is no slop in the guides, valves are not burnt and your going too use this head when you reassemble the engine. Why not lap the valves?

If you have your head apart.....use a little bit if "Extra Fine" lapping compound....give the valve a light lapping.....then clean everything up....look at the valve seating areas.....if the lapped area is symmetrical all the way around the valve and seat.....and if the lapped area is no wider than 1mm (I'm guessing as to this measurement, there will be a spec someplace in MB literature) then they are good......

Lapped area not continuous all the way around valve and/or seat.....valve leaking.....needs further checking as to cause.....

Lapped area continuous but not symmetrical.....possible bent valve or slightly egg shaped valve seat.....grey area as to repair, depends on the rest of the valves.....

Lapped area wider than spec.....valve seat needs resurfacing/grinding.....

Lapped area narrower than spec (usually only after grinding)...lap a bit more.....

The width of the valve seating area is important, mostly for performance.....but also effects the heat transfer from the valve seat to the cylinder head and the coolant circulating in there.....there are only 2 areas where heat can be dissipated from the valve....thru the valve seat, and the valve guide.....too narrow of a valve seat, valve runs hotter, to wide of a valve seat valve flow is affected (high performance issue).....

SB

Stevo · #29 06-28-2007, 10:33 AM

Thanks chief, I'll stash that valve evaluating info away for future reference. I couldn't help but get a flash of you climbing to the top of the stack of an MSC ship with a giant sheet of paper flapping in the wind while "Capt Bell" looked up from the wing of the bridge scratching his head.

I apperdiate the run down, thanks again

lietuviai · #30 06-28-2007, 11:36 PM

Quote:

Originally Posted by Shorebilly

.....I was intending to purchase a '58 Chevy Impala with the 348 Tri-Power option.....
SB

Now that would be worth some nice $$$ today. I guess you didn't buy it by guessing about your intent.

I like your lapping suggestion. I've done it on a motorcycle head "many moons ago" myself. I just might try it depending on the condition of my valves and seats.