Last week the manifold flange on my standard issue moggy exhaust fractured, so that was the goad I needed...
Doing things in stages, so as not to introduce too many variables at once, I stripped away the original manifolds and exhaust.
To fit the Metro exhaust manifold onto the studs, I had to remove the front tappet cover with the breather tower on it, but it then fitted back on OK with adequate clearance, and this was an opportunity to seal up a long term oil seepage point!
On fitting the inlet/carb arrangement, I found the throttle cable needed lengthening by about 4" to give a good sweep, also the inner needed to be even longer to accommodate the snailcam type throttle mech on the HIF38. It was easy to re-make the cable, re-sweating the pedal end nipple onto a new bit of bicycle brake cable!
The choke cable was also too short, but as I wanted to retain the original knob, I made a simple extended mounting bracket for the carb end, and extended the inner using a section of 15 amp electrical "choc block" to splice a bit more brake cable inner on!
The custom exhaust fitted nicely, mounting from the original hangers, but it is a bit tight getting twin downpipes through the hole in the bulkhead!
She started up a treat, but needed 2 more turns on the needle jet adjuster to get some semblance of order.
Immediate impressions were smoother low speed running, and a distinct desire to keep pulling where previously she got winded! I did have to play tunes on the choke to get the mid range to accelerate smartly, but was not over-worried as I knew the next stage would alter things again.....
Next morning broke sunny again, so at 6.30AM I started stripping the standard moggy head off.
First thing to do was to centre the rockers onto the 940 head exhaust valves. I found the thick washers at each end of the rocker shaft just the right thickness (about 1/16"), and my box of assorted seat belt mounting bits yielded two more suitable 9/16" bore washers. One fitted between each exhaust rocker and adjacent pillar, inlet rockers are fine as is.
Next I wound the exhaust adjusters out a bit to avoid any possible embarrassment with block interference when initially bolting the head down...
Then a couple of thumps on the battery carrier to provide clearance for the heater valve, which sits at a different angle on the 940 head!
Next a goodly amount of protective rag around the block, and with an angle grinder I linished about 1/16" off the top of the water pump flange which sits proud of the block face and would otherwise foul on the underside of the 940 thermostat housing...
The head dropped on easily, but is tight going past the guard on the radiator top tank, so mind your fingers ( I didn't!)
The rear engine steady bracket needed a notch cut out of it to clear the new angle of the heater valve. I radiused the corner of this notch to avoid a possible stress point forming.
Once bolted down, with number 1 pot on tdc compression, I set its valve gaps. Then cautiously (plugs out for ease of turning) hand turned the engine til number 1 exhaust was fully open. Using a large screwdriver as a pry bar, I further pushed the rocker until the valve touched the block face, this was a good 1/16", note this was with no sinking mods done!
Feeling infinitely more confident, I set the remaining clearances, checking each exhaust valve similarly as I went, then replaced the plugs and turned my attention to the thermostat housing. The 940 head makes the top hose connection exit at a different angle which looks a bit ukky, but the bellows type top hose didn't seem to object! I understand that the housing from a pre 75 MGB fits at a better angle, if it is of great concern to anyone.
So the cooling system was refilled, remembering (though not at first!) to tighten the clamp on that horrid little bypass hose, and the starter pulled. She struck up a treat, immediately much more responsive when "blipped", and now goes like stink from mid range (55MPHish) upwards, wanting to carry on well past the end of the speedo, though as I still have to juggle the choke to get her there, I am not going to pursue that too much until she has been set up on the dyno. Spirited acceleration leaves the clutch trying to catch up with the engine when changing from 2nd to 3rd, so I estimate considerably more than a~7BHP increase already! Indeed the Holy Vizard et al seem to infer that a good 5BHP can be expected just by unstifling the exhaust so I might anticipate nearer a 12-15BHP increase when all is set up. I will let you know in time!
Note I am using a standard 998 Metro needle, opinion seems to point to an AAA being close to what you need which would presumably avoid the choke juggling act, but I will leave that to my dyno A-series expert!
A full 220mile tank check shows comparable fuel consumption to my previous records, which considering the silly way I have been using the thing and my natural pessimistic stance gives hope for a win-win situation when all is sorted out!
I hope the above is of help to anyone considering these or similar mods.
PLEASE DO CHECK your anticipated exhaust valve lift using measurements from your existing set up as, although mine went fine, others have had to do some pocketing. Then bolt the 940 head down without all the ancillaries, (but not torqueing down) to set your mind at rest (or not) about your actual clearance, that way if you need to do any pocketing, you can re-use the head gasket. Torqueing down will only account for a small reduction in gasket height, say .008"/.010", so should not be too significant in your calculations.
Now, can someone give me similar details on fitting a Marina box onto the engine
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