Why do you have to cut the seat when you replace valves

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Model T Ford Forum: Forum 2016: Why do you have to cut the seat when you replace valves
Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Kirk on Tuesday, September 27, 2016 - 12:04 pm:

In a recent post called Oil in valve spring area it was said that the seat has to be cut if you replace the valves but in an older post it was said you do not

Sherm Wetherbee on Thursday, February 05, 2009 - 05:32 pm:

"Question 1 replace all valves with stainless steel. The original are two piece and there is a possibility of the head coming off the stem the head then punches a hole the the piston on the next upward stroke. Question 2 the cast iron insert requires special machine work and the block has to be removed from the car. Question 3 Unless the seats are very worn there is no problem lapping in new valves to the old seats. The grinding marks will tell you if you have a good seat and seal. I would strongly recommend new valve springs. The original valve springs have usually lose a lot "spring" At least check them should have 25-28 pounds at 2 inch compression"

He states that it is possible to lap the new valves.
Is that true?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim on Tuesday, September 27, 2016 - 12:08 pm:

You can lap them in. If they are not at the proper angle or the seat is damaged you'll be at it for a very long time. Easier and faster to do it right the first time though.


Top of pagePrevious messageNext messageBottom of page Link to this message  By KSK, South Texas on Tuesday, September 27, 2016 - 12:43 pm:

Ditto on faster and easier. If you have it down that far, give the seats a few quick swirls with a Neway cutter and be done with it. It's likely that the old valves have worn, pitted or burned gaps into the seats.

Too much lapping will cup the valves and round the seats. Lapping is required if you grind the seats. Not so with Neway cutters.

http://www.newaymfg.com/frame.htm


quote:

Valve seat reconditioning is simple, accurate, and clean with Neway’s carbide-bladed cutters. Neway’s user-friendly cutters allow you to precisely machinene a multi-angle valve seat in a matter of minutes. Grinding valve seats with stones is a messy process and relies heavily on the finesse of the operator. Grinding also requires the additional task of seat lapping to complete the job. That’s because the surface of a stone is constantly changing as it works, so it can’t create a truly flat surface. Carbide doesn’t change as it works, so there’s no need for lapping. Tungsten carbide leaves a perfectly flat, machined surface, ideal for optimal sealing efficiency and heat transfer.



Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, September 27, 2016 - 12:48 pm:

First check how worn the valve guides are. If too worn, it's best to ream the guides for oversize valves first - then cut the seats :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Adam Doleshal on Tuesday, September 27, 2016 - 12:59 pm:

Many times the valve guides are not worn evenly all the way around. Usually when intake valves start to suck oil enough to make the engine smoke you may have a clearance of around .008". Usually this clearance is all off to one side because of the tendency for the valve spring retainers to pull the valve in one direction or another. When you ream the guides to the next oversize the reamer will naturally follow the rough center line of the worn-out bore. Odds are that the valve was settling into its seat and sealing, but when sealed, wasn't necessarily centered in the guide. If the top and/or bottom of the old bore is worn off center the fresh guide hole is very likely to not be exactly on the same center line as the old guide hole. Most times, the newly reamed guides end up being a couple thousandths of an inch off center with the existing seats. Even .002" is quite a lot of material to remove by "lapping the valve". You can do it, but it might take a LONG LONG TIME... When you finish lapping and take a look at the contact pattern of the valve to the seat, you are likely to find that the seat makes contact with 100% of the valve on one side, but the contact is razor thin on the other. This is where seat grinding is handy. A 45degree seating surface is ground based on the location of the newly reamed guide. Then that is followed by grinding with a 30degree and 60degree stone above and below the seating surface in such a way to "narrow" your 45degree seat to a contact pattern that is ideally about 1/3 the width of the valve's 45degree sealing surface and centered near the middle of the seat. Making the seat contact too wide is generally avoided because contaminants have a better chance preventing the valve from fully seating and potentially burning. Making the seat to narrow is generally avoided because the valves contact pattern with its seat when closed is what transfers heat to the block and prevents them from burning.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Adam Doleshal on Tuesday, September 27, 2016 - 01:11 pm:

The "newway" cutters are okay too if you happen to know someone that has them.

You should be able to find someone in your local area that can ream your guides and properly grind all the seats for a total of $100 (if the engine is out)

If you need the work done in the car, some shops should be able to do that too... HOWEVER, clearance is so close on some cars that they may not be able to adequately access the rear valve seat and you may end up with a substandard job on that last seat...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Trent Boggess on Tuesday, September 27, 2016 - 06:05 pm:

The Montana 500 is one of the most interesting events in the entire Model T hobby. The Montana 500 is an over the road race for "stock" Model T Fords that is composed of 10 timed segments. The winner of the race is the competitor with the fastest time over all 10 segments. For the purposes of this race, "stock" refers to a Model T with fitted with a regular production body, chassis and motor. Ruckstells cannot be used, and if present on a car must be disconnected from the shifter. Cars must have the standard 3.63 to one rear axle gears. Carburetors must be stock, and the standard 4 coil Ford ignition system must also be used. At the end of the race the three fastest cars must go through tear down to check for compliance with the rules.

Given these rules, how is it that the winning cars typically go through the course at an average of 54-57 miles per hour?

I have been fortunate to know several Montana 500 racers, and even more fortunate to watch them as they build up their cars. The cars really are stock Model Ts.

How they get them to run so fast is not all that big of a secret since everything is stock. Montana 500 motors are built up out of carefully selected parts, and they are carefully balanced. But where these car builders really lavish their time is in the valve train. A stock Model T high head has a very low compression ratio. So the engine builders I have observed spend a lot of time on 1) valves and seats, and 2) on valve timing.

Here is what I have learned. The valves themselves, even if new, are faced at 44 degrees in order to get a slight interference fit, and ground to have .0005" total runout of the face to the stem. Similarly, the valve seats are machined to have total runout with respect to the valve guide of .0005 or less. The contact between the valve and the seat is checked by making about a dozen little back hash marks on the valves face, the putting in the valve and turning it by hand on the seat. If you have a good seal, the hash marks will be cut at the point of contact with the seat, and the width of the cut in the hash marks indicates if the seat's 45 degree angle is wide enough. Grinding the valves with compound really isn't necessary.

It seems to me that most of the Montana Engine Builders have their own special grind on the camshaft, but I suspect that the camshaft grind of the home brew cams is not that far off between a Stipe, Chaffin, or Carnegie ground camshaft. All three seem to work well.

So when you do the analysis, what is important is that when the valves are closed, they are tightly closed. The valves are timed, usually with a degree wheel, to make sure they open when they should, open as far as possible, then close when they should, and tightly. In effect they are trying to get as much of a fuel/air mixture into the cylinders as possible, then bottle it up as tight as possible, and light it off. Good valves and seats, properly fitted, are a major contributor to good Model T engine performance.

I use Neway valve seat tools, and have an old Sioux 645 valve facer that I can coax into grinding a valve with .0005 runout. You have to have at least 3, and maybe 5 pilots for each valve guide size (nominal, .001, .002 undersize and oversize), a valve seat runout indicator, and lots of practice. For me, it takes a special feel and hold of the seat cutting tool to achieve my goal of .0005 runout. It takes time and patience to get the valve faces and seats just right. But, when it is done right (especially using new inserts in the exhaust and intake seats in the block) the results are, for me, very rewarding. The valve jobs are also very long lasting.
Most Model owners who are rebuilding their engines will take the striped block to a good automotive machine shop which as a valve seat machine. These machines will produce a very accurate three angle seat in a lot less time than I can. For more information on this step in the engine rebuild process you should watch Mike Bender's excellent YouTube videos on Model T engine rebuilding, especially the video on cutting valve seats.

To summarize, don't try to save money on an engine rebuild by doing a cheap valve job. Spend the money, and have it done right. You will be glad you did.

Disclaimer: There are other participants on this forum who do Model T valve jobs more often and maybe with better results. Listen to them. I always do.

Respectfully submitted,

Trent Boggess


Top of pagePrevious messageNext messageBottom of page Link to this message  By J and M Machine Co Inc on Wednesday, September 28, 2016 - 06:43 pm:



To Quote Trent Boggess: "To summarize, don't try to save money on an engine rebuild by doing a cheap valve job. Spend the money, and have it done right. You will be glad you did."


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A Bartsch on Wednesday, September 28, 2016 - 10:56 pm:

Dear J & M: How much contact area is there between the valve and seat in the pic above? I assume the contact/seal is at the top edge of the cone surface, essentially a circle, with very little area?? Thanks, jb


Top of pagePrevious messageNext messageBottom of page Link to this message  By J and M Machine Co Inc on Thursday, September 29, 2016 - 10:03 am:

James:
The seat width is about .070" wide and this seat has a 60 degree angle below and a 30 degree relief angle on top. This is what is referred to as a 3-angle valve job.
Hope this helps.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach, CA on Thursday, September 29, 2016 - 11:57 am:

A lot of modern quick valve jobs use the two angle cut. They grind the seat at 45 degrees and the valve face at 44 degrees. This gives the largest opening with a contact width of about .012" to .025" after it normalizes it's self through hammering. It works well and a lot of shops use this method. The three angle cut is the very best.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Trent Boggess on Thursday, September 29, 2016 - 02:17 pm:

Disclaimer: I am not an automotive machinist, nor do I play one on TV.

There are several different ways to machine valve seats, and the method used at J&M is one of them. Their seats look good, and as Frank Harris points out, their valve jobs should last a long time.

I was taught to do it slightly differently. I have three Neway cutters: 30, 45, and 60 degrees angles. I use all three in order to get the width of the 45 degree seat where I want it. Also remember as I stated in my earlier post, I grind the faces of the valve to 44 degrees. Modern steel valves aren't quite as rigid as you might think. The head will flex a tiny amount as the valve settles onto the seat. I could be wrong, but I think my method will produce the same final results as J&M. I do know that when I have used this technique, the valve jobs last a long, long time.

One last point I think I should mention here. You still have to make sure the valve guides are machined correctly as well. There should be about .0025" clearance between the valve stem and the valve guide. As my mentor explained it to me, the valves have to "rattle around" a bit to settle onto the seats properly. I don't much care for the notion of a valve "rattling around", but I do understand where he was coming from.

Oh, and finishing the valve guides is an art unto itself...

The tools to do this work are expensive. You need to buy the Neway cutters and an assortment of guides, a valve seat runout gage to check your work, a true automotive valve guide reamer of the proper size, a Sunnen portable hone to smooth up the finish and to remove enough valve guide material to give the proper valve stem to guide clearance, and a Sunnen valve guide gage to be able to measure the diameter of the guide at different points in the guide. The cost of the tools are non-trivial. In truth, you are much better off taking the stripped block to a qualified machinist who already has the right tools and the experience to do the job right.

I know that at least 5 such people who are active participants on this forum. When they make a comment here, listen to them!

I don't save any money, and probably it takes longer to do the job than if I sent it out to one of these engine re-builders. But I enjoy the work, can challenge myself to produce the best job possible, and I have a heck of a lot of fun doing it.

Respectfully submitted,

Trent Boggess


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthonie Boer --- Klaaswaal NL on Thursday, September 29, 2016 - 02:37 pm:

What do you think about this FORD TOOL.
Toon
1484aboer


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Thursday, September 29, 2016 - 04:10 pm:

Peter,

In a nutshell, if the valves were bad enough to need replacement then the seats can't be much better. Also, if the valve guides were worn enough to need reaming, the newly reamed guides will NEVER be concentric to the old seats. No amount of lapping will fix that and the seats need to be cut to get them right.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A Bartsch on Thursday, September 29, 2016 - 09:04 pm:

Thanks J & M, Trent and others. The information in this post should be added to the MTFCA repair book. jb


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach, CA on Thursday, September 29, 2016 - 09:16 pm:

Jerry you are right on dead center on that one.


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