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  #1  
Old 12-17-2003, 09:08 PM
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Lapping valves question 75 240D

Okay, it's now rookie time here. I have the head off and was cleaning up the valves and wanted to lap them. When I pulled them the seats and valves where they contact each other are very, (like chrome) shiney...

So I take number one intake and start lapping and the surface turns grey, okay I think this is normal...?

I need a reality check here. Are the valves and seats in a 616.916 motor chromed such that I should not lap them or is this normal that they look like they are chromed and I should continue on with the balance of the valves?

In other words, HELP!

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  #2  
Old 12-17-2003, 09:16 PM
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Do you have a spec for the valve seat margin? Yes the contact area will turn "grey" when lapped, completely normal. AFAIK the only hardened area of a valve is the stem where the rocker pushes down on. I don't see how lapping the valves would be a bad idea, should be a good thing, making sure the they all seat correctly and the margin widths are in spec. RT
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  #3  
Old 12-17-2003, 10:53 PM
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Phew...

I thought that somehow I was maybe removing the chromed edge of the valve and seat that was factory or something...
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'85 300SD Silver - Sold
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  #4  
Old 12-17-2003, 11:21 PM
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Are you going to install new valve rotators " on principal" as the factory shop manual suggests ?
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  #5  
Old 12-18-2003, 01:49 AM
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Nope, no chrome, just fairly hard valve and seat, and the valve rotates. If they are shiny and the sealing faces are flat, there isn't probably any need to lap them, but it won't hurt. Just lift the valve often, and go easy, you don't want to grind slots in the valves!

Cheap and cheeful way to check is to take the rockers off and put water on top of the valves. They will all be closed, and if no water leaks out, they are fine.

Peter
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  #6  
Old 12-18-2003, 11:35 AM
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Peter and Greg

Thanks Peter. The head is off the car so I thought I might try to rig up a low pressure air connection to the manifold side of the motor. Then use a soap solution to look for bubbling. I think some amount is to be expected but a pass-thru leak without holding any pressure is probably not good. I wonder if I could use my MityVac and pull a low vacuum on the cylinder side? could be a problem getting a good seal on the head though.

Greg,
I was going to replace all 8 or the rotators until I pulled mine out and find them all seeming to work fine. I noted that in a post that I researched someone said something about them clicking ("so they do not rotate too much")but there are only one or two of my rotators that don't "click" but feel kind of like there is a bad ball in a bearing (if you know what I mean)... The rest are pretty smooth.

at 10.00 a pop I'm inclined to leave the old ones.

Interestingly I found one cap nut on an exhaust valve that had a groove driven into it as if the cam has been hitting this one in the same place for soem time. When I pulled the valve I could see why. The stem seal was leaking and the valve had so much sh__ built up on it that I doubt it could rotate! There were a couple of exhaust valves taht had this buildup. Interestingly none of the intakes but perhaps that is because the oil that leaks past the seal just gets sucked intot he cylinder and that the valve itself is probably not as hot since it is sucking air in rather than expelling burnt gases.

You will be happy to know that all my Prechambers are fine though!!!...

One parting question. My local indy suggests replacing the chain tensioner since it is original. This part is pretty spendy. Is there a consensus on whether or not to change this part "just because"? I am leaning towards using the old one and then checking it after all is back together. that's one part you can actually replace after everything is back together without too much of a headache.

Once again this forum proves it is the best!
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  #7  
Old 12-18-2003, 02:24 PM
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Self-rotating sodium filled valves - used to be $38 each...... same as the cylinder head, dont let some guerrilla "chevy mechanic" talk you into grinding them down to smitherines, removing too much metal...... surface metal is different from the core to accomodate heat absorption - yet they will burn up entirely if you grind em too far down. Dealership will tell you NEVER grind sodium filled valves - just replace them instead.


Last edited by 300SDog; 12-18-2003 at 02:55 PM.
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  #8  
Old 12-18-2003, 07:42 PM
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Thanks Dog.

I'm just applying a very fine lapping compound and attempting to get a better seat not a re-seat if you know what i mean...

I have no additional funds for parts so I'm taking it easy and just touching them up. It's gotta be better than they were...

One more question... In lapping with fine grit i.e. 520 I think (the can is in the garage) about how much time would be normal to twist the valve just to touch up a seat?
I know this is 1. a little weird to ask and 2. not an easy answer but I am afraid that I am being overcautious and i have no mentor looking over my shoulder to say "that's perfect" or "geez ease up a bit".
Right now I'd say I averaged on the last valve only about thirty seconds or lapping with this grit of compund.

Thanks for the input
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  #9  
Old 12-18-2003, 08:35 PM
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How much side to side play, as in valve guide wear?
Pull valve down about 1/4", and see if it moves sideways, one hand on the valve stem, one hand on the valve head.
If it moves more than a couple thousands, probably valve guide time, exaust vavles are more prone to guide wear.
I use solvent to test valve seats, just pour into intake/exhaust ports, if it runs out valve seat, not good.
Oh, use paint thinner, a lot cheaper than solvent, that's what I use now, same thing, darn enviromentalists.
If you have a dribble in about 30 secounds, should ok.
When grinding soduim valves, do not use water based coolent in the valve grinder, they can explode, use atf fluid and be gentle.
True the grinding stone often.
Lapping valves in will take a long time to wear much metal off, unless your're doing it with a drill motor, which I have seen some people do, lubricate the valve stem if you use this method, but I don't recommend the drill motor method.

Last edited by russb; 12-18-2003 at 08:47 PM.
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  #10  
Old 12-18-2003, 09:39 PM
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gimme a low-tech 240D
 
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Russ, whatsa 'valve grinder'?? Used to be suction cup on stick that was stuck to the valve in its seat with some fine pumice paste applied to the seat and then rotated by rolling the stick between palms of hands, like Indian starting campfire....... very time consuming and slooow procedure, something you do while watching football on tv.... Thats the method I'm familiar with.
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  #11  
Old 12-19-2003, 02:37 AM
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gimme a low-tech 240D
 
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If it was me, i wouldnt turn the engine at all.... but would have paint marked the timing chain to camshaft sprocket for easy reassembly.
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  #12  
Old 12-19-2003, 06:44 AM
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The suction deal is only for the final stage... actually called ' lapping' as compared to ' grinding' which uses a trueable grinding stone to get a flat and correct angle face on the valve seat or the valve..
These guys have a really nice paper catalog ...

http://goodson.com/

"Is there any way to check my rings from the top to see if they are okay?" Nice try.... but no... no way....

CHANGE THE TENSIONER ! and the GUIDE RAIL ALSO...
most chains do not break themselves... they are screwed up by one of these two items... particularly if they are original.. this is actually a no brainer once you think about it...


Last edited by leathermang; 12-19-2003 at 06:52 AM.
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