TheSamba.com :: View topic - Lap Used Int. Valves & New Exh. Valves to Uneven Cut Seats

Wed May 06, 2020 10:35 am

Hello!

I sent a set of cylinder heads to a local mechanic for a valve job. I checked guide wear with a dial indicator per the red VW engine rebuild book, and guide wear was within spec.

The mechanic replaced the exhaust valves, faced the valve stem tips that were concave worn (look a little rough??? hopefully OK??), and ground the valve seats.

I worked with a knowledgeable VW friend and removed valves to check out the valve job. He examined them and said that the seats were ground, but they looked "uneven."

I plan on buying some blue layout fluid so I can check the current valve/seat contact pattern before doing ANYTHING. (any tips on this?)

So here's my final question....is it acceptable to lap new exhaust vavles to seats that are not cut perfect?

I'm trying to grow in VW engine knowledge. Thank you for helping me in this endeavor.

(pictures to come)

Wed May 06, 2020 11:24 am

yes...but why are they uneven? and by how much?
assume this is for a stock application?

Wed May 06, 2020 11:30 am

NateDJ wrote: Hello!

I sent a set of cylinder heads to a local mechanic for a valve job. I checked guide wear with a dial indicator per the red VW engine rebuild book, and guide wear was within spec.

The mechanic replaced the exhaust valves, faced the valve stem tips that were concave worn (look a little rough??? hopefully OK??), and ground the valve seats.

I worked with a knowledgeable VW friend and removed valves to check out the valve job. He examined them and said that the seats were ground, but they looked "uneven."

I plan on buying some blue layout fluid so I can check the current valve/seat contact pattern before doing ANYTHING. (any tips on this?)

So here's my final question....is it acceptable to lap new exhaust vavles to seats that are not cut perfect?

I'm trying to grow in VW engine knowledge. Thank you for helping me in this endeavor.

(pictures to come)

There is really no way to answer your question without seeing and measuring everything. How the cut looks on a seat depends on how worn they were and how wide the seats were to begin with. It also depends on where he set his cutter for a contact point. Were the ports vacuum tested to make sure they sealed? Is there a reason you are worried about the contact pattern?

To answer your last question, I have never lapped a valve in a head in 30+ years of doing this. We cut the seats, assemble the head, vacuum test the port and then I put it on a motor or ship it out.

Wed May 06, 2020 1:48 pm

You can use a sharpie instead of dye, for what you are doing

Wed May 06, 2020 2:02 pm

no dont lap it, if the seat aint concentric to the stem it's junk. Ive seen some morons do a valve job to wore out heads with wore out junk for seat cutter and push this way or that way to get the seat to cut everywhere.....how fucking stupid. the valve job needs to be right. needs to be round. needs to be done with no runout or wonkey ness. needs to be smooth.no smoother than that... still needs to be smoother. many morons dont know what a proper seat looks like. and these morons are charging for this....

Wed May 06, 2020 6:47 pm

Yes, marker.
Color the seat and valve with some black marker, put the valve in and rotate it back and forth 1/4 turn, observe contact pattern.

You certainly can't tell anything from looking at it.
You CAN tell by feel if the seat is concentric, but you gotta know how.

Wed May 06, 2020 7:41 pm

I don't like using lapping compound to see the seat contact / concentricity. I feel it's very misleading. Lapping compound tends to just show the largest area of seat contact all around the valve because you are twisting when you lap. There is usually enough viscosity to the paste to gray up the whole seat unless it's really bad. It may however repair slight irregularities in the seat. You can lap a valve, have everything look nice and gray, and then it still can fail a Prussian blue check or solvent test.

For checking valve to seat contact, the best bet is to use Prussian blue paste. Smear a thin coating on the valve, tap it with your finger into the seat, then push it out (without twisting) and you will see the contact pattern.

Wed May 06, 2020 10:13 pm

vwinnovator wrote: yes...but why are they uneven? and by how much?
assume this is for a stock application?

I was told they are probably off because they were uneven when I brought them in.

I’m not sure how to judge how far out they were. I’ll be bringing them to a machine shop tomorrow for a vacuum test.

Sorry, yes stock application.

Wed May 06, 2020 10:15 pm

mark tucker wrote: no dont lap it, if the seat aint concentric to the stem it's junk. Ive seen some morons do a valve job to wore out heads with wore out junk for seat cutter and push this way or that way to get the seat to cut everywhere.....how fucking stupid. the valve job needs to be right. needs to be round. needs to be done with no runout or wonkey ness. needs to be smooth.no smoother than that... still needs to be smoother. many morons dont know what a proper seat looks like. and these morons are charging for this....

I’m bringing them to a legit machine shop tomorrow to have them leak tested. Thanks for your input. I’m too green at this to know by lookin at them, but my trusted friend was concerned with what he saw.....seats not concentric to the stem...just like you said it.

Wed May 06, 2020 10:17 pm

modok wrote: Yes, marker.
Color the seat and valve with some black marker, put the valve in and rotate it back and forth 1/4 turn, observe contact pattern.

You certainly can't tell anything from looking at it.
You CAN tell by feel if the seat is concentric, but you gotta know how.

Appreciated. I’m bringing them to a legit machine shop who does all our businesses Diesel engine machine work. He’s going to check them out for me. Very skilled person.

Wed May 06, 2020 10:17 pm

esde wrote: You can use a sharpie instead of dye, for what you are doing

I have a small jar of layout fluid, but I’m bringing them to a legit machine shop tomorrow. Thanks

Wed May 06, 2020 10:19 pm

Nightshift wrote: I don't like using lapping compound to see the seat contact / concentricity. I feel it's very misleading. Lapping compound tends to just show the largest area of seat contact all around the valve because you are twisting when you lap. There is usually enough viscosity to the paste to gray up the whole seat unless it's really bad. It may however repair slight irregularities in the seat. You can lap a valve, have everything look nice and gray, and then it still can fail a Prussian blue check or solvent test.

For checking valve to seat contact, the best bet is to use Prussian blue paste. Smear a thin coating on the valve, tap it with your finger into the seat, then push it out (without twisting) and you will see the contact pattern.

Appreciate thank you. I’m bringing them to a machine shop tomorrow to have them checked. I’ll post back my results.

Wed May 06, 2020 10:23 pm

[email protected] wrote: NateDJ wrote: Hello!

I sent a set of cylinder heads to a local mechanic for a valve job. I checked guide wear with a dial indicator per the red VW engine rebuild book, and guide wear was within spec.

The mechanic replaced the exhaust valves, faced the valve stem tips that were concave worn (look a little rough??? hopefully OK??), and ground the valve seats.

I worked with a knowledgeable VW friend and removed valves to check out the valve job. He examined them and said that the seats were ground, but they looked "uneven."

I plan on buying some blue layout fluid so I can check the current valve/seat contact pattern before doing ANYTHING. (any tips on this?)

So here's my final question....is it acceptable to lap new exhaust vavles to seats that are not cut perfect?

I'm trying to grow in VW engine knowledge. Thank you for helping me in this endeavor.

(pictures to come)

There is really no way to answer your question without seeing and measuring everything. How the cut looks on a seat depends on how worn they were and how wide the seats were to begin with. It also depends on where he set his cutter for a contact point. Were the ports vacuum tested to make sure they sealed? Is there a reason you are worried about the contact pattern?

To answer your last question, I have never lapped a valve in a head in 30+ years of doing this. We cut the seats, assemble the head, vacuum test the port and then I put it on a motor or ship it out.

Thanks for your professional input. I’m bringing the heads to a local legit machine shop tomorrow. He’s going to vacuum test the ports for me. I’m sure your seat cutting techniques are superior to what my heads received.

My very trusted friend, Berg student, and retired engine builder was not impressed with what was done to my heads for $100 per side. He thought the seats were not cut concentric to the stems based on the way they looked in certain lighting.

Thu May 07, 2020 5:44 am

Quick and easy test: put pugs in the head and sit it level on the bench. Fill the chamber with whatever light solvent is on hand, and see if it leaks through to the intake or exhaust ports. Not perfect, but doesnt require disassembly or special equipment
Acetone works well.

Thu May 07, 2020 5:48 am

Part of your problem may be that new guides weren't installed. Any used guide, even "within tolerance" will have a slight eggshape to it.

The other possibility is probable use of only a 45* stone, and not using 30* & 70* to even out and/or narrow the seat to spec. So while it looks lopsided, the 45* may actually be OK.

The old time Germans I learned from would never lap .. just throw new valves in with freshly cut seats. For myself, I kept a box of reground valves solely for the purpose of very lightly checking the seat with a fine lapping compound. THEN I threw in the new valves. I just felt more confident doing that check.

Thu May 07, 2020 8:14 am

it can be hard to get all the laping compound out of the seat&valve and it;s extreamly abraisve. I dont use it. wont use it. none in my shop. blue or marker does just fine.as do calipers & good eyes.

Thu May 07, 2020 8:29 am

esde wrote: Quick and easy test: put pugs in the head and sit it level on the bench. Fill the chamber with whatever light solvent is on hand, and see if it leaks through to the intake or exhaust ports. Not perfect, but doesnt require disassembly or special equipment
Acetone works well.

Liquid and vacuum testing will NOT tell you the condition of the seats/valves or if the work was done correctly. It will only tell you if it seals and Nothing more. I see heads weekly that pass vacuum and liquid testing. I take them apart and see work done by either old equipment, not qualified personnel or not caring.

Thu May 07, 2020 4:03 pm

esde wrote: Quick and easy test: put pugs in the head and sit it level on the bench. Fill the chamber with whatever light solvent is on hand, and see if it leaks through to the intake or exhaust ports. Not perfect, but doesnt require disassembly or special equipment
Acetone works well.

I have a spring compressor and layout fluid, but I want my friend at the machine shop to check them out. Thanks for the idea. I'll keep that one in my back pocket =).

Thu May 07, 2020 4:06 pm

gears wrote: Part of your problem may be that new guides weren't installed. Any used guide, even "within tolerance" will have a slight eggshape to it.

The other possibility is probable use of only a 45* stone, and not using 30* & 70* to even out and/or narrow the seat to spec. So while it looks lopsided, the 45* may actually be OK.

The old time Germans I learned from would never lap .. just throw new valves in with freshly cut seats. For myself, I kept a box of reground valves solely for the purpose of very lightly checking the seat with a fine lapping compound. THEN I threw in the new valves. I just felt more confident doing that check.

I know for sure that the guides were not changed. I measured guide wear with a dial indicator and found them to be in spec before I brought them in for the valve job.

That's a possibility. I was told by the person who worked them over that he ONLY ever does a 3-angle job nowadays. Based on what my engine builder friend saw, I received a 1-angle grind, and marginal at that.

I dropped them off at a very good machine shop today for inspection. I like the idea of a well-done fresh proper seat cut, along with checking them with after with fine compound.

I'll report my findings early next week.

Thu May 07, 2020 4:47 pm

mark tucker wrote: it can be hard to get all the laping compound out of the seat&valve and it;s extreamly abraisve. I dont use it. wont use it. none in my shop. blue or marker does just fine.as do calipers & good eyes.

Thanks for your input. If I had proper guide and valve measuring training, I'd be glad check them. I regularly use a set of vernier calipers in our shop at work, but have limited knowledge of how to apply their use to top-end engine parts, especially ACVW.