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MG MGA - 1500 head questiuon

i had a 1500 head magnafluxed and it showed a crack on the exhaust valve seat about 1/4 inch long but it appears as if the seat is a machined part of the block.
what i would like to know is if the valve seats were pressed into the block or were they just a machined then
hardened area of the head


my machinist will replace the exhaust seats with the
hardened material but suggests that i should the use the
standard exhaust valves with hardened seats so that the
softer valves will mate better with the harder seats
(less pounding)
anyone know if the original seats were separate from the heads?
tks don
don wallenius

Don,
According to the Haynes manual, the seats can be replaced, implying press fit. The parts manual does not show them separately, however. It may be that your machinist is required to cut the old seats out and machine the head to fit new ones.
mike parker

Mike, the fact that replacement seats are available does not imply that the original seats are also inserts.

In fact they were cut directly in the cast iron of the heads.

If Don has a crack in his head, it has either been serviced before and the new seat has cracked, or the original seat in the cast iron has eroded.

The old MG heads didn't even have induction hardening, so they were pretty darned soft and will erode unless they ran on leaded for awhile.
Bill Spohn

Bill,
I noticed that. When I looked, I was not expecting to see that the head and seat were integral. I don't know whether there are replacement seats, or whether the machinist must get some seats of appropriate size and then machine the head for them, but it seems that way.
mike parker

The way the seats were machined in the heads during manufacture gives the apperance that they were fitted with inserts. As Bill says - original heads were not fitted with insets.

It is a fairly straight forward job for an automotive machineist to fit inserts.

Inserts come in a range of sizes, so it is a matter of choosing the correct ones and then machining a recess to fit.
Exhausts only though - there is not enough metal between the inlet and exhaust seats for inserts to be reliably retained in both in a B series head.

Standard valves are ok for normal road use, and with the harder inserts fitted you can now go lead free.

Cheers
Ian F



Ian Fraser

thanks for the input, the old exhaust seats will be machined out tommorow when he has the replacements to fit. hopefully then the old seat has been replaced already as there is no sign of pitting then it's not a crack in the head but sounds like the head should then be fine

i am rebuilding the 1600 to put in my 1500 coupe so that i can then do that motor. The crank and cam checked out fine but pistons have .013 clearance so i am going .020 over on the pistons and will probably order from MOSS. any comments on these?
tks don
don wallenius

Hi Don. Since you have the head off, and are doing a valve job, I would highly recommend installing silicon bronze valve guides, and stellite exhaust valves. These components stand up extremely well to unleaded fuel! Stellite exhaust valves shouldn't pound the seats any worse than standard valves, in my opinion. If you go with bronze valve guides, be sure that the machinist reams them oversize so that there is .002" to 0025" of guide to valve stem clearance. The bronze guides expand under operating conditions. This extra clearnace is needed to prevent valve seizures in the valve guides. Cheers! Glenn
Glenn

Before you invest a lot of money into that head, be aware of the fact that 1/4 inch of visible crack could mean that there's a bunch more that's just to tight to see. Take the head into a good machine shop and have it magnafluxed. If that crack goes beyond the area to be machined out to install the insert, you're throwing your money to the wind.
R. L Carleen

Hi Rob. I was under the assumption that Don had ascertained via the machine shop that the hardened seat would circumvent the cracked seat problem, however you raise a good and valid point. It sounds to me like Don already had the head magnafluxed, which is how the crack was discovered. Cheers! Glenn
Glenn

i did have the head magnafluxed which showed up the
crack and also that it never had new seats put in
so he now has the new seats and will machine the head
and press them in.
i found it interesting that the original seats were just
a machined part of the block and not inserts, and yes now is the time to replce the guides with silicone bronze.
good point about the clearances and valves seizure so
thanks for the info
tks don
don wallenius

DON- FYI- As the sili-bronze are "self lubricating", why not use the improved umbrella valve stem seal, SPKST 2001 ( I got'em at RockAuto LLC, Cedar Rapid Iowa for .58 each). In one testimonial on Barney Gaylord's site, oil consumption went from 500/qt to 2000/qt. By all accounts, including Master John Twist, this is a better mousetrap and huge improvement over the pathetic mini-o's included in the head set. Good luck, keep us all informed. Vic
vem myers

This thread was discussed between 06/01/2005 and 08/01/2005

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