Hi I'm new to this forum, I'm an amateur mechanic and like to give most jobs a go. I was wondering if anyone has had a go at a homemade U engine, some may say what's the point, and I'm not saying I will actually build one but was just wondering if anyone had tried and if it was simple or a pig of a job. My idea would be to build one out of two 1.9 tdi engines (AFN, 1Z) I like the simplicity of the mTDI set up and running wastegate turbos( I don't like ECU's). The mTDI style allows for the engines to go into almost any setup, and with this engine it may need to be custom mounted in the rear of a vehicle. I would be looking to use either a Bosch VE pump with T - pieced injector pipes or, a direct injection fuel pump for a V8 diesel, probably something off a big American truck. Mounting would be custom with bracing between the engines on the engine mounting points plus a plate on the back of the engines to hold them together and mount the gearbox onto. If I used a V8 pump I am assuming I could get away with custom injector pipes and a V8 firing configuration by setting the second engine 1/8th of a turn on from the first engine. Using one pump would allow for a matched ignition timing and acceleration on the engines rather than lag from either one which could cause linking problems, chain tension, etc. Individual engine timing woud be maintained by the standard set up. There are a few parts I'm not too certain on;
A suitable linking system - I saw a video on Youtube where a guy had meshed the flywheels of two dragster engines and was running them together. One engine rotated the opposite way to the other, this isn't something I would want to try, I would be thinking of attaching sprockets to the crankshaft instead of the flywheel and running a chain around them linking them to a third sprocket which would be attached to a solitary flywheel. The only thing is what would I get the chain and sprockets from that would stand up to the torque of these engines, I thought of the timing set from a V8 TDI or a motorbike drive train. Running a chain set would allow me to run the flywheel and gearbox in the same direction as the engine and so not have problems with gears, if I used a smaller third sprocket I could get the gearbox rotational speed up and so the overall speed would increase, I know 1st gear would feel more like second but the engine should take it. I would make the plate on the back of the engine in two layers, one to hold the chain, sprockets, and tensioner, the second layer to hold the flywheel and mount the bell housing onto. Probably 10mm steel plate, heavy but cheaper to fabricate than milling aluminium.
Turning the second engine internals around - I would like to mount the engines so that the injectors are facing each other, this would mean the heat from the exhausts would be on the outsides of the engine and also there is potentially more space for the turbos in that location. It would also allow for the injector lines to be neater and shorter than other configurations and allow for a shared water pump and oil filter ( both custom piping). The part I don't know is if I removed the crankshaft and flipped it over so that the timing pulley was where the flywheel should be and vice versa would the crank go back in and have the correct clearance at either end, or does the crank only go in one way. I've never stripped an engine that far so I don't know. If I remember rightly there is a cutout in the head for the camshaft timing end to sit out but once again I don't know if it would work. I know valve seats would need to be machined and swaped and if larger valves were needed the same would need to be done on the other engine to give matching power, no point in one engine carrying the other. The waterpump would need to be uprated and possibly a smaller pulley fitted for faster rotation. Service intervals would be more frequent, but this setup would mean being able to use 1.9 tdi parts and not v8 ones.
This is all from my head and probably all wrong, for me it would be a lottery win project, and a proof of concept rather than a massive performance mod, so many will say why bother but I just wanted to get the idea out there and see if it is possible and if it has been done. I've done a bit of research but there isn't many pictures and not of homemade efforts. Bugatti did one years ago but it had a common crank case. This way if a single engine were to die you could just bolt in another. The legality of this engine for UK roads would be questionable, is it two engines or is it as it's name describes one engine? You can't run one without the other as they are linked through the injection system and the drive train, but in their own right they are manufactured as separate engines and can be run separately if fitted with individual injector pumps. I would be interested in peoples ideas, but as I said this is an idea where money doesn't play a part, it is proof of concept. Thanks for reading and I look forward to your comments.