Replacing exhaust valves?

[TTait]

So several years ago a botched valve timing job led to installing a newer engine (long story). The exhaust valves banged into the pistons and the compression was shot.

The heads had just been professionally rebuilt, and have perhaps 500 miles on them. In theory the only thing wrong with them is that the exhaust valve are bent.

I'm looking at refurbishing the heads as a first step toward rebuilding the engine, and I just picked up a set of 6 new exhaust valves on ebay. I'd kinda like to do the job quickly once they arrive lest I find out they are actually for a Jeep or something.

I've read through the manual, and it refers to a valve spring compressor, and grinding/seating the valves. So...

Do I really need a valve spring compressor? Is this a generic enough piece that I can borrow one from auto zone or something?

If these are brand new valves I'm putting in, do I need to have them ground?

I've seen videos that show that you can check for a good seat using a bright light and looking for light leaks, or by pouring in water to see if it leaks through - is this a proper procedure?

I know I've seen demonstrations where you put the valve in place, apply a paste to the seat, and then spin the valves to get the seat and valve cut to match - can and should I be doing something like this? Just install the thrust washer and then spin it by hand?

Is this something I need to pay the head rebuilder to do for me?

Advice appreciated.

Tom

[WelmoedJ]

Do I really need a valve spring compressor? Is this a generic enough piece that I can borrow one from auto zone or something?

Any good automotive tool store will be able to get you one; it's a generic tool.


If these are brand new valves I'm putting in, do I need to have them ground?
Yes, you need to grind them to make them fit to the seat.


I've seen videos that show that you can check for a good seat using a bright light and looking for light leaks, or by pouring in water to see if it leaks through - is this a proper procedure?

This is one of the methods.


I know I've seen demonstrations where you put the valve in place, apply a paste to the seat, and then spin the valves to get the seat and valve cut to match - can and should I be doing something like this? Just install the thrust washer and then spin it by hand?

This is the proper way; once the grinding paste is evenly spread (or taken away after grinding) you should have a solid "seal".


Is this something I need to pay the head rebuilder to do for me?

If you have someone rebuilding the head for you, have him do the grinding job.
A company doing that and fouled up can be made responsible.

Do not forget to also use new valve seals, to prevent oil leaks (if not supplied with the valves).

[TTait]

Any good automotive tool store will be able to get you one; it's a generic tool.


Yes, you need to grind them to make them fit to the seat.



This is one of the methods.



This is the proper way; once the grinding paste is evenly spread (or taken away after grinding) you should have a solid "seal".



If you have someone rebuilding the head for you, have him do the grinding job.
A company doing that and fouled up can be made responsible.

Do not forget to also use new valve seals, to prevent oil leaks (if not supplied with the valves).

If its generic I'm sure I can borrow one. We can't get health care in this country like you have, but at least our parts stores will lend out such tools. Ha!

Looks like I need to dig up some paste, engineers blue, and a kids toy arrow with a suction cup on the end (maybe my old buddy Joe Dalton has one of those laying around?), and get to work ... Sounds like fun.

I hope the ends of the valves are at least machined flat...

[WelmoedJ]

If its generic I'm sure I can borrow one. We can't get health care in this country like you have, but at least our parts stores will lend out such tools. Ha!

Looks like I need to dig up some paste, engineers blue, and a kids toy arrow with a suction cup on the end (maybe my old buddy Joe Dalton has one of those laying around?), and get to work ... Sounds like fun.

I hope the ends of the valves are at least machined flat...

Usually the "valve ends" at least wheer they seat are machined flat, but need the finishing touch to match the valve seat in the cylinder head (ahhh.... you know that :D )
I've got suction cups for windshield mounted GPS, but not for grinding valves.
As you know, would love to come, but this is not possible now.

Some pics of our latest meet in Belgium (gives you some "back in time" views).
404040394038

[Delorean Industries]

If your current valves in the head are bent and the engine has been run the seats will need to be cut. Lapping the valves will not do the trick. You will also need to replace the valve stem seals. Another thing to watch out for that I have seen a lot here is worn guides. If the valve is not contacting the seat properly it will put stress on the stem wearing the guide.

[dn010]

I've seen videos that show that you can check for a good seat using a bright light and looking for light leaks, or by pouring in water to see if it leaks through - is this a proper procedure?



An "old school" method of checking to see if the valves have been lapped correctly is to of course use the grinding compound on them, clean the goop off and then take the valve out. On the valve itself - draw a few lines / hash marks down the area you just ground - I used to put about 8, one on top, bottom, left, right, and then ones in between those. Then you reinstall the valve (dry) and use the suction tool to spin the valve - if the pencil marks wore off then you've got a good seat - if not then you're back to using the tool and grinding compound...

[David T]

Lapping (polishing) the valves in is a finishing touch that many rebuilders no longer do. The equipment today can do a very accurate job and no longer requires lapping. It should only be done after having the valves and the valve seats and guides ground. You need a "twiddle stick" and some lapping compound and a LOT of patience. A large auto supply should have it (not the patience). When lapping you do it till you have an even band of dark all across and around the valve sealing surface and the valve seat. It should be about 1/4 inch in height. Among the techniques to "blueprint" a head is to lap the valves in, port, polish and gasket match the intake and exhaust runners and bowels, unshroud the valves, test each spring for pressure and shim for height, cc each combustion chamber and match them all up, index the spark plugs, deck the heads, etc. This can get VERY involved and to some is almost a religious ritual. All work should be checked on a flow bench. If you don't know what you are doing you can actually make things worse, not better. Best to let a good shop do the work but I doubt you will find anyone familiar enough to know what to do with the heads for a PRV. Bottom line it won't make a big difference anyway unless you change the cams and dump the stock exhaust system.
David Teitelbaum

[TTait]

There is a place nearby that does nothing but rebuild heads. I took these heads there several years ago, and told the tech that they were our of a Volvo, and asked if he could rebuild them. He said they were similar to volvo, but not technically volvo, and asked if they came out of Delorean. It may have been a parlor trick but it was enough to impress me.

While the work then was actually pretty cheap, the results seemed very good. The valves were all replaced at that time. The car ran very well with taller cams, but due to some very unfortunate work by a good mechanic the exhaust valves got bent within 500 miles or so, maybe a third of that.

I think my plan then is to get some lapping compound and engineers blue paste, and just try lapping the valves by hand. If the blue shows a good seat, then I'm golden, right? If not, then I have to wait till I have the cash to take them back to the rebuilder.

Is this a reasonable plan? If they seat well and I use new seals and guides I would expect to be in good shape. At the same time I'll expect that it won't work, not getting my hopes up.

[David T]

Lapping won't work on used/worn valves , guides, and valve seats. You have to grind the valves and seats first and if the guides are worn they have to be replaced. You don't need the bluing, besides, once you use it you can't use it again unless you can wipe it off completely and you can't. I like Dychem but it doesn't come off, it isn't supposed to! To check how bad the valve seals are you place the valves in the head (no springs) and fill the combustion chamber with water. It shouldn't leak out. Then you measure run-out with the valve off the seat to check for wear in the guides. If you do not have a lot of miles on the heads and they were not overheated you should be able to clean them up yourself. Decarbon them, wire brush them and the valves, replace the valve seals, check the surfaces with a straightedge, and you should be OK. You can spend a LOT of money on head work and not have much improvement to show for it.
David Teitelbaum

[TTait]

Not sure I can do the water test, the heads are off the car and the depression in the head will only hold an oz or two of water. I might be able to silicon a plastic cylinder on and do it that way.

The way I have seen bluing done, you clean up all the paste, then put a really thin film on the valve and then spin it a little on the seat - if the bluing transfers 360 degrees around you have a good seat, if not you lap more and repeat. Even if all the bluing doesn't come off when you lap more, the goal is to get 360 degree coverage, right? Why can't you keep doing it, I thought that was the point.

The heads only had a few hundred miles on them when a botched valve adjustment job (good mechanic - bad mistake - moving on) led to the damage seem below.

There was no overheating. The mechanic called and told me I'd lost compression on all 6, and that my liner seals must have blown out, so we put we a newer engine - upon disassembly I found the actual damage and an pretty sure that's why the compression was toast.

I can take the heads back to the shop that rebuilt them the last time to have the valves properly installed, I was just hoping with only a few hundred miles on the heads I might still be able to lap fresh valves in and go. A professional rebuild will have to wait a while.

[David T]

You don't silicone. You take a large glass cylinder open on both ends and grease up the edge. Then you place it around the combustion chamber and fill with water. If you bent valves they cannot be straightened, only replaced. The valve guides must now be checked, they could be bent or egged out. From the pattern of lapping you can see how well the valves are fitting to the valve seats, you do not use bluing. When you start the valve face and the seat face will be shiny. As you lap in the valves you will start to produce a grey band. The more you lap the wider the band will become. You will wear the paint off the twiddle stick.
David Teitelbaum

[TTait]

You don't silicone. You take a large glass cylinder open on both ends and grease up the edge. Then you place it around the combustion chamber and fill with water. If you bent valves they cannot be straightened, only replaced. The valve guides must now be checked, they could be bent or egged out. From the pattern of lapping you can see how well the valves are fitting to the valve seats, you do not use bluing. When you start the valve face and the seat face will be shiny. As you lap in the valves you will start to produce a grey band. The more you lap the wider the band will become. You will wear the paint off the twiddle stick.
David Teitelbaum

So while lapping might not work, if I am able to get a good seal myself hand lapping, I've saved a bunch of money it sounds like. Cant hurt to try?

[TTait]

I thought I saw someone selling a kit complete with head gaskets, o rings, cylinder shims of all colors, bearings, etc etc etc - I thought it was Houston - but I don't see it now. Anybody know where I saw that?

[opethmike]

I thought I saw someone selling a kit complete with head gaskets, o rings, cylinder shims of all colors, bearings, etc etc etc - I thought it was Houston - but I don't see it now. Anybody know where I saw that?

This guy?

http://www.delorean.com/store/p-6063-gasket-kit.aspx

[TTait]

Thanks - thats it. Looked under kits, searched for the individual components - just didn't look there again - thanks.

[TTait]

Valves installed, lapped, and it looks like there are excellent seals. Won't know for sure till its all back together, but I have nice satin grey bands evenly all around all 12 valves (I went ahead and hit the intake valves too while I was doing it, they already seated nicely so it was just a matter of touching them up to remove any carbon etc.

Lapping paste and dowel from Napa, and I got a nice spring compressor from Harbor freight for about $15.

Thanks guys.

[David T]

You might want to put a little oil on the valve seats and once assembled do a compression check as a baseline and to verify you got everything assembled correctly and are getting compression. All of the cylinders should be within 5%, especially after a rebuild. If they are not squirt some oil into each cylinder and try again. If it improves you have worn rings.
David Teitelbaum