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948 head

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59frite

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well its a beauty day here in the northwest, wish i could get out and enjoy it.

i figured out whats up with the frite. it turns out that the ex valve in #4 is burned. the good news is that the pistons and cylinders still look good.

the head that was on the motor (948) is a 2A 29(?)casting.-might be another number in the middle there, cant really tell- i have 3 or 4 other heads laying around and one is complete from a 1098. that is a 12G295 casting.

my first thought was to scavenge one of the valves from that head and just have it and the seat ground. cheap, easy and would get me through the summer. but first thing i noticed is that it appears to be a bit smaller than the one in the 2A 29 head.

so the question is, what is the difference between these heads? what engines did they come from? and what is the preferred head for performance on a 948? 1098? 1275?

the 2G 29 head that was on the motor is one that my pop massaged. he relieved the sharp edges in the combustion chamber and i believe he did some work to the ports too. the goal is to eventually put together a 1275. would this head work on that block? would it be a good choice?

thanks in advance
chris
 
Check Visard chap 9 for a complete discussion of head types, swaps, etc.
 
IF it were me I would have the 12G925 head refurbed and cc'ed to 24.5cc.
inlet valves are bigger and the ports are too.


casting no, Valve INLET DIA Valve Exhaust Dia. chamber cc.

2A629 1.0625"/26.99 1.00"/25.4 24.5 948, A35 & Morris Minor
12G295 1.218"/30.93 1.00"/25.4 28.3 998 Cooper, MG1100
 
Yep! Use the 12G295 head, it is what your dad was trying to make the '29 into!
BillM
 
thanks for the input!

i'll be doing my research before i have a head done. that will include getting a copy of vizards book.

after talking to the guy at the local british car shop i decided to just replace the valve with one from another head. one of the things he cautioned about was the difference in the the combustion chamber size. the 295 has a larger combustion chamber and would therefor lower the compression ratio. he even suggested using the 629 head with the bigger intake valve. its not an issue right at the moment. as i sad, i replaced the valve, lapped it in and put it back together. i'd say that $25 to fix a burned valve is a pretty good price. it runs real good and i might even be able to tweak the carb a little closer to perfect.-ya right lol-

anyway, thanks again for the input. tomorrow morning i can go get the license tabs and it will officially be on the road again!!!
 
I think that what you're suggesting makes a lot of sense. Do the quick and dirty fix that gets you back on the road so you can enjoy the summer, short as it is in Seattle, and put your time and money into the 1275.
 
And that is why I suggested Vizard. The 295 head will work but only with quite a bit shaved off of it to keep the compression the same.
 
well its official. it runs and runs dam fine too. i spent most of the day yesterday just driving. did get reminded of 2 things. first gotta conserve that momentum. once it leaves, it takes a bit to get it back. the other is that it handles real twitchy. it just wants to turn. i imagine there is some play in the rear suspension that adds to that feeling. but its still a blast to drive.

thanks again for the ideas, and yes it looks like the frite will join me over in snohomish on the 18th!
 
Glad to hear you're back on the road!
 
As for usng small bore heads on 1275 engine, that would be a no-no. you had the bore in different location so to speak, you had different valve spacing, of course you could smack 1275 valves into the 948 and 1098 blocks.
 
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