Timing problems, may now revise my engine, what are metro pistons capable of?
Turbo Mini Forums

A few years ago I built up an engine which I intended for turbo use.

It mainly consisted of a low mileage non mg metro bottom end, sw5 cam, and a Austin 1300gt head. This was a time when I was very short of cash, so had to build on a tight budget. I reconditioned the head as it had been sitting for a while, I relapped the valves in, changed the exhaust valves for a plus items, and changed the rockers for ‘S’ bushed items (aprox 1.4:1 ratio). I calculated the CR at around 9.25:1, planned on running around 10 psi of boost and aimed for around 100bhp

At the time I put the engine together I had never timed an engine in properly. I set the duplex gears to dot to dot.

Things have moved on since then. I am looking at installing the engine into the car soon. I tried to check the timing this evening trying to find top dead centre through the spark plug hole, but this was impossible. I kept getting different readings each turn of the engine (I guess because the vernier was at an angle on a dished piston, so there was slight movement across the crown each time).

So I will be taking the head off to time this engine properly with vernier gears. When its off I will probably port it as I have had a go at a few and have got good results so far. I may also open the chambers out slightly to lower the CR further. This would enable me to run slightly higher boost at safer levels. My main concern though are the pistons, being standard metro items. How much boost can these withstand? I don’t want to go crazy opening the combustion chambers up to run high boost if the pistons will not be up to it.

Im changing the car from spi to run a carb, plus megajolt as well. This is all rather daunting at the moment, but I will get there with it. I plan on building a higher spec engine in the future, but want to get this one sorted first to make sure I can get the car to run with the proposed changes. I really want to leave the bottom end of the engine alone for now. I know not the ‘right’ way to go, but I want to make sure I can get the car going before building anything else.

So what are the metro pistons up to? I will also be using a cossie intercooler and have the car properly set up

you dont need to take the head of to get a good tdc reading,

get an old spark plug, and knock the insulator out, IIRC a head stud will fit in it fairly well, weld the head stud in so it sticks out about 3/4" you can then wind this in and use it as a "dead stop"

with the dead stop in and a protractor on slowly turn the engine one way till the piston contacts the dead stop, nore the degrees, then turn the engine the other way til it touches the dead stop, move the protractor by half the diference between the two readings and it should be right. obviously repeat and tweek in needed until you get the same reading at either dead stop

thanks for this mini13. i will give it a go ion the next few weeks. just not had time recently! again, many thanks