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Old 07-06-2016, 08:31 AM   #1
Bobby DiDomenico
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Default Valve seat issues

Have helped a friend with a few of their Flathead Straight-8 and V-12 engines. This one was rebuilt about 2 years ago and has cylinder pressure issues, to the point he removed the head and lapped the valves. It seems all the intake seats (and valves) lapped well. The exhaust seats seem to exhibit an hourglass shape. You can see the dark areas where the lapping compound is not reaching. Some of the exhaust valves had a noticeable cupping when you lay a straight edge against the seat. He said it was running hot but it is with a 1931 factory gauge. It did not use any water on a trip to Texas which was aborted in MO. where he checked compression and returned

I did not see how the shop did the valve job, so I don't know if the block or cutter were moved along. (While the cylinders come off the V-12, this engine must weigh over 800 pounds so I don't see them moving it around easily.) Any idea why the intakes don't exhibit the same issues? If it was cutter induced I'd have guessed all would show the same pattern. Any ideas?
I really, really, really, don't want to disassemble the car and remove this thing again. :-)
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Last edited by Bobby DiDomenico; 07-06-2016 at 08:34 AM.
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Old 07-06-2016, 08:47 AM   #2
Billy Nees
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Default Re: Valve seat issues

Exhaust lash not set correctly? Exhaust guides too tight? Flatheads are different animals than OHVs when it comes to heat.
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Old 07-06-2016, 09:00 AM   #3
SST3193
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Default Re: Valve seat issues

Is it caused by the lack of lead and the fact that the exhaust valves get hotter than the intakes? Am I correct in assuming there are no hardened valve seats?
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Old 07-06-2016, 09:04 AM   #4
Bob Shaw
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Default Re: Valve seat issues

It looks like the guides are slightly offset in the block. New guides?
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Last edited by Bob Shaw; 07-06-2016 at 09:09 AM.
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Old 07-06-2016, 09:14 AM   #5
Bobby DiDomenico
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Default Re: Valve seat issues

Don't know if the heat did it Billy, even in this state you could still balance a nickel on it while it ran.

This engine does not have hardened seats. They (the shop) replaced them in the 1929 8, don't know why they decided not to do have them do this one.

None of the odd spot pairs are perpendicular to the crankshaft, they are all on some diagonal variation. If there was a wobble with the cutter could it have induced this pattern? I'm missing how.

Bob, the guides are original he says.

Last edited by Bobby DiDomenico; 07-06-2016 at 09:33 AM.
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Old 07-06-2016, 10:34 AM   #6
Billy Nees
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Default Re: Valve seat issues

Quote:
Originally Posted by SST3193 View Post
Is it caused by the lack of lead and the fact that the exhaust valves get hotter than the intakes?
Just an FYI, I got a good tip the other day about older engines. Put about an ounce of Marvel Mystery Oil per each 6-7 gallons of gas. Also works well in older engines with mechanical injectors. Diesels too.
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Old 07-06-2016, 01:01 PM   #7
Tom Goldman
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Default Re: Valve seat issues

I do some driveline work for a shop that specializes in Packards and they started experiencing valve seat wear similar to this many years ago .
They believe its due to heat generated by modern day gas having a much different burn rate than gas of the '30's.
Engine cooling also is effected by the use of glycol coolant as opposed to the alcohol mix that was used back then. It may not overheat ,but the dissipation rate is different .
They now use Evans Coolant in these type of cars
They install hardened seats in everything now and have no problems .
Also if the tappet face is worn or has not been resurfaced properly the valve may not be rotating.
X2 on Billy's suggestion , Marvel defiantly helps on these old engines ,especially the valve guides.
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Old 07-06-2016, 01:15 PM   #8
Bobby DiDomenico
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Default Re: Valve seat issues

Thanks guys. These cars all have serious drivability issues with todays gasoline, especially the ethanol summer blends we are forced to purchase here.

Tom, I'm afraid that cutting the seats again and removing more material is going to make it worse. The fact that there is not left to right issues seems to back up your cooling idea. My guess they now have antifreeze for sitting over the winter, he used to run maybe just some type of water in all of them? I'll find out.
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Old 07-13-2016, 11:35 AM   #9
Bobby DiDomenico
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Default Re: Valve seat issues

Exhaust manifold issue, any ideas on what could have caused this? Is a weld and machine a lasting repair? There is just a small area of material connecting the top and bottom portions that I'm estimating to be .125 deep. The exhaust valve to the right was the one with the worst seat issues. You can see the gasket is no longer sealing on the top of the ports where the manifold portions are no longer in line and eaten away.
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Last edited by Bobby DiDomenico; 07-13-2016 at 11:38 AM.
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Old 07-13-2016, 12:42 PM   #10
Tom Goldman
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Default Re: Valve seat issues

Blast clean it to remove the carbon and pre heat to around 500 deg to help cook out any remaining carbon.
I TIG repairs like that using NickelCast 55 stick rods with the flux removed , makes a very nice ,durable repair ,especially on old castings.
I've used this method for blocks , heads and manifolds.
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