OK, I have a CA head with sticking valves, two bad exhaust valves and valve seats. I'm thinking, with the proper ream, I can clean up the guides. I can buy a valve seat cutter to clean up the two bad seats. I have a couple used valves to replace the burnt/cracked ones. lap all eight valve/seats and I'm back in business....right?
Anybody see any problems with this plan? one I see is the cost of the valve cutter.
I'm weighing the viability of this plan, chance of success/cost v finding a good used head.
all input appreciated
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If that is all that is wrong with yours I would fix it. You never know what you are getting with a used "good" head.
1975 7040 w/Power Director
Does the seat cutter come with the correct size stem for your guides? The older I get the more I'm in favor of do it yourself fixes although I must admit I don't have 100% success.
You can grind the valve heads and the seats at the same time with valve grinding compound and a tool to rotate he valves in place.Shop manual may describe that method:Gerald J.
Thanks Gerald, I know that can be done, but these seats have a pretty good 'trough' around the circumference, where the valve wore right into the seat.
I have the oscillating tool that fits in the drill, I guess it wouldn't hurt to try, that would cost nothing except some grinding compound
I am still confident of this;
I will see the goodness of the Lord in the land of the living.
Wait for the Lord;
be strong and take heart and wait for the Lord. Ps 27
Labor is all the same, to R&R head, head gasket, and re-torque. Likely you can get the whole job done at a good machine shop, I think the last head I had the guides knurled, seats ground, and head pressure tested, for less than $500, and the seat cutter and other tools you might need will likely cost you more than that...
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Lou, many many years ago I did what you are thinking of doing, that used valve cost me a complete engine rebuild after about 100 hours of run time after used valve was installed.
It is actually lapping compound that you use to do a final mating of the valve and seat after cutting them. Won't do any good on messed up parts.
1975 7040 w/Power Director
At one time, you could buy valves with oversized stems and run a reamer through to refresh the guides to round. Don't know if they are available anymore.
I would not bother with used EX. valves but put new ones in on recut/replaced seats...
If your going to run it only a few hours a year, cheap should be sufficient but if your going to use it hard, get her done right.
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If you feel confident in your ability then go ahead and do the seat grinding yourself. The tool is expensive but next time you won't have to buy the tool when you need it! I would not recommend using used exhaust valves, new ones are $10 or less new. While you have the head off, I would freshen up all 8 seats and freshen up all valves unless the face that contacts the seat is not grooved. Then use your valve lapping compound to lap the valves to the seats to make sure they seal good.
Unless you come across a rebuilt head, might as well fix your own instead of buying a good used one.
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Just my opinion ,just because people can buy tools to do the job, dose not mean they can do the job with the tools.
Good luck .
Make sure seat width is correct to the valve .
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I would never try to reuse valve guides. They are cheap and easy to replace. The new ones. The ones you would take out would have a head on top and the new ones do not. Some have a scribe line for the depth. The guides that don't you just measure. I ground a block for the height. I ground a punch pin with a pilot to go inside that was slightly smaller on the outside than the guide. I mostly used a press to remove and replace the guides. I have also used the punch and a hammer.
Lapping is a final step in sealing up the valve to seat. Lapping until you have groove is short term at best. I was taught to spark the new valve faces in the 1950's and would still if I was doing them now.Sparking a new valve is only seeing a spark as it rotates slightly against the wheel.
I have rebuilt heads on the shelf. New valves, guides, springs, and keepers. manifold and head surface machined. Tested for cracks. $350.
There ya go Lou. Cough it up and be done.
$350 is a good deal for what it includes, if you don't have to pay for shipping.
Valve guilds can make or break a long term valve job. Intake clearance, generally runs .001 - .002 and exhaust clearance .002 - .003.
To much intake clearance leads to pulling oil into the combustion chamber. If you see build up on the under side of the valve, the guild has way to much clearance.
To much exhaust clearance will contaminate the oil, caused by exhaust gases getting into the crankcase.
Bronze valve guilds are preferable, if you can get them. They last longer and will stick less.
Good guilds means that the equipment doing the grinding, both the value and seat, needs to be accurate. With only .001 - .002 clearance, to work with the valve run out shouldn't exceed .001 or, the valve will hit the seat, off center.. Thoughs of you that have value grinding machines, need to check the run out, with a new valve, in place. Check it with 7/16, 3/8 and 11/32 valve stems, to be sure the chuck isn't warn over any part of that range.
For valve seat grinders (or cutters), the guild for the stone and the stone arbor needs to be in good shape. If the guild isn't in the center of the of the valve guild and well seated, the seat will off center of the valve.
When you lap, use Dykem or a wide felt tip pen, to mark the valve seat, lap until you get a pattern .045 - .060 on the intake and .060 - .085 on the exhaust. Then, came back with a 15 deg stone for 30 deg seat or a 30 deg stone for 45 deg seats and grind to your lapped pattern. You should also touch up the the inside of the seat, with a 45 or 60 deg stone or cutter. I like using cutters for this, stones like to grab and chatter, as well as break.
One other thing, if you have a value grinder, break the back edge of the value seat, at 15 deg less, it will increase flow. You can reduce it to the valve contact area or so. Do this when you first grind the valve or to new valves. It also helps with lapping.
Last, if you don't have hardened exhaust seats, have them installed.
Edited by frnkeore - 19 May 2019 at 1:32pm
Frank
1959 D17 Series I #24001+, '59 D14
'55 & '59 Ford 850 & 861
Ferguson TO 35 Deluxe, Oliver 70 and 5 more.
Valve lapping is quite a curious engineering process which of necessity I've studied in detail over the years. Prolonged lapping, especially with coarse paste, actually makes the seating surfaces of the valve and head insert concave so the two only make contact on their inner and outer edges. This is obviously very bad for heat dissipation as well as airflow. I can see the effects of heavy lapping very clearly on my valve refacing machine or head seat cutting machine as the grinding wheel or cutter makes initial contact with the concave faces and only touches them along the edges.
You can also easily see the concavity on a valve after prolonged lapping by putting a high quality straight edge across the seat and holding it up to the light. Try it on an old head some time. The mechanism at work here is that the paste on the inner and outer edges of the contact area quickly squeezes out as you start lapping leaving most of the abrasive action taking place along only the centre line of the seat. So lapping can't restore a badly cut or badly worn seat properly as they used to think in't olden days. It might have sufficed for a 30 bhp per litre truck engine from the 1940s but is not what you want for today's high performance machines generating much more heat which needs dissipating properly through surfaces in perfect contact with each other.
However a very light lap with fine paste for just 10 seconds or so to check that the valve and seat are truly concentric and with no high or low spots is a good idea and not a problem. If there isn't an even grey contact area all round both valve and head seat after that then it's probably time for remedial machining rather than further lapping.
For many years now I've used special diamond grit based paste rather than the normal carborundum grit paste you get in little tins with two lids for coarse and fine at each end from car accessory shops. It's horribly expensive but it has a completely different abrasive action which I can't really describe but it's much nicer. Being so hard and sharp, diamond grit abrades the surfaces really fast before the paste has had time to squeeze out and the grit particles don't break down into powder immediately like carborundum does so you don't get the concavity and it takes less time to check that the surfaces are making good contact. However the fine paste from those little tins is perfectly ok for general use. The coarse paste is a definite no no.
I used to have a customer in the early 90s for whom I did the CVH heads for his race car along with many other people's. They generally got a quick refurbish mid season and it took me a while to work out why every time I recut the seat on one of his valves (but no one else's) they were badly concave and only touching the grinding wheel on the inner and outer edges. After speaking to him it turned out that every time I sent a finished head back, despite my own quick lapping to check the seats were perfect he'd stand there for half an hour grinding them in further before assembling everything thinking he was contributing to the general cause and doing some good when in fact he was just buggering up my delicate machining work. After actually showing him what his tinkering had been doing to the concavity of the seats there was one of those "oh sh*t what have I done?" expressions on his face and he left things well alone after that.
In OE engine production valve seats are never lapped which would be horribly time consuming to do on every engine but of course there are constant quality control checks being carried out to make sure the valve and head seat surfaces are being machined to a perfect specification. They also sometimes use a very slightly different angle on the seat in the head and the seat on the valve, maybe half a degree or so, to make the two components "hammer" into full contact after the engine is first started. Not my idea of perfection engineering really. Unfortunately you can't just assume that Joe Bloggs your general engine reconditioner is even capable of cutting proper valve seats which most aren't in my experience so checking them with a quick lap is essential. The much vaunted Serdi machine which is the popular choice these days is a bugger for cutting non concentric seats in the head if there's even a fraction of a thou of valve guide wear. I prefer seat cutting systems with fixed rather than rotating pilots like the Sunnen system.
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