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'74 head mods-what should I do?

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artmck

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I have my engine out for other reasons and am considering a bit of exhaust port work as recommended on the British Automotive site. I need to research exactly what to do, but I was wondering if it is worth the effort, and if it is advisable to skim the head a bit for a minor compression ratio increase.

It seems fairly obvious to remove the little tubes that stick into the ports for the air injection, and maybe just clean the ports up a bit. Would a high quality valve job be noticeable in term of flow increase? As far as I know, engine is totally stock, but I'm not sure about any earlier rebuild efforts until I measure stuff.

Thanks-
 
I have seen that page in the past and I'm sure it is a nice outcome. What I was wondering is if it is worth the effort to do just some basic cleanup in the ports to an otherwise stock and good running engine.

Would it be noticeable either in performance or just a bit sweeter running?

Thanks
 
IMHO You would notice more improvement by losing twenty pounds. Possibly a SLIGHT improvement on the dyno but nothing in the seat of the pants. Bob
 
Hey guys,
I got a 71 mg midget 1275 and wanted to get more performance. David lieb, and DonG., Treavor jessie, and Bill Young, all recommended to port and polish the intake and exhaust. I found out they used abrasive material to do porting and polishing, aka.. like gritty sand. So yesterday...sunday after the spridget50 at lake ozark, I decided to try it My self. I got a bag of sandblasting sand and hooked up into the 2 intakes of the 2 SU Hs2 carbs and started the car. I had to hold the gas pedal all the way down so it would run. I wanted to let the engine suck in as much of the sand as was possiable through the intake so it would port it out and then push it out the ehxaust so it would port the exhaust manifold and help clean up the valves as well.
After running the car and letting it suck in the sand I got about half way through a 25 lb bag. The engine Started bucking and kicking and sounding really weird. So I stopped and hooked the car back up normal and took off the sand supply. I tried to start it again and it was really hard. Once started it couldn't idle and the engine kept making weird noises. SO I took it out and drove it, thinking maybe I just needed to clear out some of the extra sand and it started to make scraping and knocking noises.
Help! Can anyone tell me if this is normal, or is this a timing issue, as the carb holes look really clean...the parts guy sold me some "seafoam" but I think he was lying about it working as he seemed to want to laugh at me, under his breath....any help would be greatly appericated.

BTW...Im autocrossing next weekend....and need to have my midget up and driving full bore by then.

thanks
Just a member
 
Hey Prop - nice to see you over here.

Your unique 'humor' will be an entertaining addition to this place!

:wink:
 
I'm shakin' in me boots!!! Read with incredulity and am now about due for a new keyboard... There's CAB ~ALL OVER~ TH' PLACE!!

Geez, prop... That wuz awful. If'n ya'd said Ajax cleanser I'd likely jus' be sittin' in me own 'wet' pants. As it is I gotta clean up a REAL mess!

Thanks a whole bunch. :smirk:
 
Just run some seafoam through the carb, and next time use a fine grain non-silica sand instead of playsand and you'll be fine. :thumbsup: BTW, you could use a bit of pepto down into each sparkplug hole, then turn the motor over easy with the coil wire removed while gently rubbing the oilpan. Car will feel better in no time at all.
 
........skipping back to the *original* question, before this thread was hijacked....

<span style="font-weight: bold">artmck:</span>

If your car has 30,000+ miles on the head, at least pull the valves and pay special attention to the #3 exhaust valve.

There is a known issue with MGB cylinder heads that causes that valve to run hotter than the others and burn away quicker.

If there is any high temperature erosion on the face of that valve (or any others), replacing it with a new one is pretty quick and easy. The valve seats are usually fine, even if the valves are pretty worn.

For a muffled street car with a mild cam, I'd guess that porting would make only the slightest difference.
Probably not worth the effort unless you are also adding a bunch of other go-fast parts and intending on running it real hard.
 
aeronca65t said:
There is a known issue with MGB cylinder heads that causes that valve to run hotter than the others and burn away quicker.
Click to expand...

Particularly with the "later" post-'69 engines. Some attention to the Clive Trickey (honestly!) head treatment can yield some real benefit. Smoother idle, higher performance. The casting for the 18V heads was a compromise.
 
"If your car has 30,000+ miles on the head, at least pull the valves and pay special attention to the #3 exhaust valve.
There is a known issue with MGB cylinder heads that causes that valve to run hotter than the others and burn away quicker."

Yup, happened to my 1974 B.

The sand post above reminded me that when Chevrolet first came out with their 265 V8 for the 1955 model year it had a problem with excessive oil consumption. Seems the piston rings would not seat properly. There was a factory bulletin that instructed Chevrolet mechanics to dump a can of Bon Ami cleanser down the carburetor throat to 'rough up" the cylinder walls to help seat the rings.

Colin
 
Would you feel a difference?

Almost certainly not. This isn't a night and day change. I've done this on a stock engine and on the race track could not tell any seat of the pants difference, but noted that I was now slowly passing cars I had been behind previously.

If you never run the engine to red line anyway, I'd save the money. If you want to continue to tune the engine, then all of this work is THE necessary first step - if it isn't done, no amount of money spent on cams, compression or carbs is going to get you much.
 
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