30-05-2021, 08:49 PM
(This post was last modified: 30-05-2021, 08:52 PM by John Cornforth.)
Hi again
I know that bore wash can have alarming effects. It seems to me that you have got to get this engine running, hot and preferably under a realistic load driving the car rather than on the bench. Once the oil is hot there is no way that the lower cylinder walls should be short of oil ! I guess you could add a little two stroke oil to the fuel for an initial period (or genuine Redex if you can find any) to keep the upper cylinders lubricated. Then the essential running in process can begin. There are as many opinions on running in as there are A7 owners, but an oil that allows controlled ring/bore wear is better than one that is too "good". Some just say use the cheapest to start with, and change it very frequently.
The carb doesn't "know" about CR, it only sees airflow and is calibrated to give the right amount of fuel for any given airflow assuming a standard engine. The new head might change this requirement slightly, but I would start off with standard jetting. I don't think Austin bothered re-jetting when the Ruby HC head and 3 bearing setup was introduced. Take a look at your jets and make sure they are stamped with the right number, haven't been got at by poking wire up them and the two in the bottom of the bowl have a fibre washer underneath. Also worth checking that the needle valve is fully cutting off and has the right thickness washer under it, the petrol level should not be so high that fuel exits into the venturi unless air is actually flowing past.
Several people have had spark plug troubles of late, and I'm inclined to think that modern production techniques and materials may assume clean running modern engines and the plugs are thus more inclined to foul and then misfire when excess oil or fuel is encountered. Could be worth having a spare set to swap to at the first sign of any trouble.
A timing setting checked by strobe at 20 crank degrees maximum advance sounds like a good starting point. 20 degrees at the flywheel is about 1.8 inches /45.4 mm, and 20 degrees at the camshaft pulley rim is about 0.37 inches / 9.4 mm. In theory the later DK4 has an advance range of 16 crank degrees, so the static advance will be 4 crank degrees. I don't know the Powerspark specs.
Stopping after a few minutes could be due to all sorts of things, but that sort of timescale suggests heat related. This would include ignition components like condenser, coil and plugs. I take it that it's not simply something getting tight after warmup, and that cranking over on the handle isn't more difficult ? No doubt you have seen the recent thread about valve stems seizing in the guides when warm.
Anyway, enough rambling - keep the faith !
I know that bore wash can have alarming effects. It seems to me that you have got to get this engine running, hot and preferably under a realistic load driving the car rather than on the bench. Once the oil is hot there is no way that the lower cylinder walls should be short of oil ! I guess you could add a little two stroke oil to the fuel for an initial period (or genuine Redex if you can find any) to keep the upper cylinders lubricated. Then the essential running in process can begin. There are as many opinions on running in as there are A7 owners, but an oil that allows controlled ring/bore wear is better than one that is too "good". Some just say use the cheapest to start with, and change it very frequently.
The carb doesn't "know" about CR, it only sees airflow and is calibrated to give the right amount of fuel for any given airflow assuming a standard engine. The new head might change this requirement slightly, but I would start off with standard jetting. I don't think Austin bothered re-jetting when the Ruby HC head and 3 bearing setup was introduced. Take a look at your jets and make sure they are stamped with the right number, haven't been got at by poking wire up them and the two in the bottom of the bowl have a fibre washer underneath. Also worth checking that the needle valve is fully cutting off and has the right thickness washer under it, the petrol level should not be so high that fuel exits into the venturi unless air is actually flowing past.
Several people have had spark plug troubles of late, and I'm inclined to think that modern production techniques and materials may assume clean running modern engines and the plugs are thus more inclined to foul and then misfire when excess oil or fuel is encountered. Could be worth having a spare set to swap to at the first sign of any trouble.
A timing setting checked by strobe at 20 crank degrees maximum advance sounds like a good starting point. 20 degrees at the flywheel is about 1.8 inches /45.4 mm, and 20 degrees at the camshaft pulley rim is about 0.37 inches / 9.4 mm. In theory the later DK4 has an advance range of 16 crank degrees, so the static advance will be 4 crank degrees. I don't know the Powerspark specs.
Stopping after a few minutes could be due to all sorts of things, but that sort of timescale suggests heat related. This would include ignition components like condenser, coil and plugs. I take it that it's not simply something getting tight after warmup, and that cranking over on the handle isn't more difficult ? No doubt you have seen the recent thread about valve stems seizing in the guides when warm.
Anyway, enough rambling - keep the faith !