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Head Off - 1275 - Recommendations

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pakiwi

pakiwi

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I finally have the head off my 73 1275 MG Midget. It was blowing smoke at startup. I have attached a photo of the middle two cylinders where you can where see the antifreeze being built.
I have a spare Smog head which is in good condition. Should I get new valves, seats and guides and build on new head or see what needs to get this cleaned up.
Apart from the smoke at startup, car was running great.
Please let me know if you need further info or photos.
Thanks,
Allan
 

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I'm sure that the guys who do more engine building will have a lot more to say than I can, but I'll say this much. If it were my head, I'd start by disassembling it, getting it cleaned up, checked for flatness, all that stuff. Then the valves can be checked and you can decide if more work is needed. Since the head is off, it's a good time to do anything that is approaching necessity, but I wouldn't do anything unless there is a good reason for it.
 
Have it magnafluxed to see if it's cracked, if not then a good "rebuild" is in order; surface grind to ensure flatness, grind the valves and seats, replace the guides etc. and should be good to go.
Roy
 
I am in the process of rebuilding a 1275 head now. You can take this as far as you want. I have my head Magnafluxed, surface ground flat, ported, polished, new bronze valve guides, valve seats ground and valves ground all using David Vizard's book. I started looking into the rocker assembly and found it to be a POS. I am machining roller rocker arms and replacing the rocker shaft. Ask yourself these two questions: 1) How far do I want to go? and second: How much do I want to spend? This is a spare head for me so I am still driving the car and in no big hurry to get the new head on the car.
 
If the head doesn't have hardened exhaust valve seats suited for unleaded fuel, now is a good time. I do that kind of work if you don't find a local machine shop you feel comfortable with, a cylinder head is easy enough to ship.
 
Hap,
If I send it to you I may be tempted to do some more work on it.
One question, how long a line up do you have.
Thanks,
Allan
 
Hap,
Mine is a 74 head with the smog ports for an air rail. Is it safe to say it has hardened exhaust valve seats already? If not, where can I purchase these hardened seats?
 
None of those heads had hardened exhaust seats inserts from the factory, the factory did do a hardening treatment to the exhaust seat (but that was later with the MGBs, and 1500s), but it didn't work, believe it or not they didn't even put hardened seat in the MGB or BL model up through the production ending in 1980. Not to say someone could have already did this, but if I look at 20 heads maybe 1 out of the 20 has hardened inserts. The deal with them even more so than the dreaded valve recession, is that the metal in the head at the exhaust seats loses it's temper from the unleaded gas, and the seats will not hold a seal at the seat.
 
Hap,
Are these hardened seats something you manufacture or can they be purchased somewhere?
 
Hap,
Never mind. I found all the information I need.
 
I've heard horror stories of hardened seats coming out, since they're just press fit into place. Is this a realistic concern? Also, I wonder if it's really necessary for a car that is just a weekend driver.
 
I contacted a local MG expert and he explained that hardened seats are better than without. However, the first unleaded fuels introduced were inferior to leaded fuels and caused the pitting and wear that Hap described. Today's unleaded fuels are much better because of additives and other technological advances so that the pitting is not the issue it was. He told me that I would be long gone, read dead!, before I see the kind of deterioration I saw on my rebuilt head. I have decided not install hardened seats based on this information.
 
pakiwi said:
Hap,
If I send it to you I may be tempted to do some more work on it.
One question, how long a line up do you have.
Thanks,
Allan
Click to expand...


Not too long fiquire a three week turn around on the samll jobs like this. Ah don't worry I won't talk you in to anyhting you don't need:smile:
 
Dadandson said:
Hap,
Mine is a 74 head with the smog ports for an air rail. Is it safe to say it has hardened exhaust valve seats already? If not, where can I purchase these hardened seats?
Click to expand...


You buy harden exhaust seats from any of the popular British part vendors, check with your machine though, some machinist like to work with their own seats.
 
Sarastro said:
I've heard horror stories of hardened seats coming out, since they're just press fit into place. Is this a realistic concern? Also, I wonder if it's really necessary for a car that is just a weekend driver.
Click to expand...

Yeah, they can by people not knowing how to properly do them, I put exhaust seats in every head I do.
 
Dadandson said:
I contacted a local MG expert and he explained that hardened seats are better than without. However, the first unleaded fuels introduced were inferior to leaded fuels and caused the pitting and wear that Hap described. Today's unleaded fuels are much better because of additives and other technological advances so that the pitting is not the issue it was. He told me that I would be long gone, read dead!, before I see the kind of deterioration I saw on my rebuilt head. I have decided not install hardened seats based on this information.
Click to expand...

That is incorrect, we have data showing how even though you can machine a nice looking seat in what appears to be a undamaged seat, they won't hold seal, he would know this if leak tested his work at intervals and documented most heads without hardened seats in them fall off in leak down test after a very short time, the main problem is with #2 and #3 exhaust valve as this is the siamese exhaust port so it deals with the most heat. And before someone ask, should you do just #2 and #3 exhaust seats, why chance it is my answer. This is not a expensive thing, you want to do it once and be done.
 
Let Hap do it all then it will never need to be done again.
 
Do it right and send it to Hap. Oh, and take a few extra thou off to up the compression too.
grin.gif
 
Jack,
I would love to get it all done, ported and shaved, but things are a little tight being a Pastor at the moment. I have a call into a local chap that if he is not able to help, it will be taking a trip to NC.
Keep you updated.
Thanks,
Allan
 
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