Hello,
I hope somebody here can help me.
I am new to model engines (although my day job is developing car engines) and particularly glow plug engines.
A few years ago, I bought some plans for a 4-stroke, opposed-twin, glow-plug engine from VTH in Germany (see attached picture). Earlier this year, I finally got all the machining finished and the engine assembled (I was having to fit it in around my job and other commitments). I then couldn't get the thing to start: it would cough a bit but not actually run. After some investigation, I came to the conclusion that one cylinder was breathing better than the other so decided to try running it on just one cylinder. I removed the other cylinder and head completely (so that I had, effectively, a single cylinder engine running in a twin's crankcase and on a twin's crankshaft). I finally got it running on one cylinder, using the head from cylinder one and the barrel, piston, rod and cams from cylinder two.
Upon further investigation, I came to the conclusion that the valve seats in the cylinder heads were much too far recessed into the heads, so that the valves were being shrouded when they opened and were not allowing sufficient air into and out of the cylinders (this was due to a mistake I made when fitting the valve seats). This wasn't as bad on cylinder one as it was on cylinder two (hence using the head from cylinder one when I actually got the single cylinder engine running). I also concluded that the cam profiles were probably better on cylinder two than cylinder one (due to manufacturing errors when making the cams) (hence using the cams from cylinder two when I actually got the single cylinder engine running).
I therefore decided to remake the cylinder heads with less recessed valve seats. I have done this and, apart from the valve seats being less recessed, I am pretty confident that the new heads are identical to the old ones. Nothing else has changed (the cams are exactly as they were before) but I still can't get the engine running; and I now can't even get it running on only one cylinder, as I did before.
I've got it set up as single cylinder engine, and it seems to be breathing ok (when I hold my hand over the exhaust during cranking, I can feel air pumping out and, holding my hand over the inlet, I can feel air being sucked in). I've also done a compression check and that seems to be OK. The glow plug glows when connected (I've even checked this by removing the cylinder head with the glow plug in it and connecting it up). The only other difference, apart from the new cylinder heads, is that it is now winter and probably about 5ºC in my garage (about 41ºF). If it was a spark plug engine, I would be checking that I had spark and also checking the spark timing but glow plugs don't have a timing, I suppose. I haven't got around to trying to set the carb up, yet, so it could be fuelling poorly, but I have tried cranking it while squirting the fuel into the inlet using a perfume sprayer (the fuel is a model engine fuel which is, I think, a methanol, nitro, oil mix). It should, at least, cough, while doing this; and, last time, back in the summer, it did run with the carb I am using, so I would hope that the fuelling is approximately ok.
I am thinking of trying two further things: a) using EasyStart, as you use for getting car engines started, when they don't want to and b) warming up the whole engine with a blow torch before cranking it and spraying the fuel into the inlet as before.
Has anybody got any suggestions, at all, as to what is going on and why I can't get the thing started, even on the one cylinder? Or any ideas as to what to do next? I am so unfamiliar with glow plug engines that I am a bit lost. The only knowledge I have of glow plugs is of the ones you use in diesel engines to aid cold starting.
Thank you for any help, advice tips or even just comments that you can offer.
I hope somebody here can help me.
I am new to model engines (although my day job is developing car engines) and particularly glow plug engines.
A few years ago, I bought some plans for a 4-stroke, opposed-twin, glow-plug engine from VTH in Germany (see attached picture). Earlier this year, I finally got all the machining finished and the engine assembled (I was having to fit it in around my job and other commitments). I then couldn't get the thing to start: it would cough a bit but not actually run. After some investigation, I came to the conclusion that one cylinder was breathing better than the other so decided to try running it on just one cylinder. I removed the other cylinder and head completely (so that I had, effectively, a single cylinder engine running in a twin's crankcase and on a twin's crankshaft). I finally got it running on one cylinder, using the head from cylinder one and the barrel, piston, rod and cams from cylinder two.
Upon further investigation, I came to the conclusion that the valve seats in the cylinder heads were much too far recessed into the heads, so that the valves were being shrouded when they opened and were not allowing sufficient air into and out of the cylinders (this was due to a mistake I made when fitting the valve seats). This wasn't as bad on cylinder one as it was on cylinder two (hence using the head from cylinder one when I actually got the single cylinder engine running). I also concluded that the cam profiles were probably better on cylinder two than cylinder one (due to manufacturing errors when making the cams) (hence using the cams from cylinder two when I actually got the single cylinder engine running).
I therefore decided to remake the cylinder heads with less recessed valve seats. I have done this and, apart from the valve seats being less recessed, I am pretty confident that the new heads are identical to the old ones. Nothing else has changed (the cams are exactly as they were before) but I still can't get the engine running; and I now can't even get it running on only one cylinder, as I did before.
I've got it set up as single cylinder engine, and it seems to be breathing ok (when I hold my hand over the exhaust during cranking, I can feel air pumping out and, holding my hand over the inlet, I can feel air being sucked in). I've also done a compression check and that seems to be OK. The glow plug glows when connected (I've even checked this by removing the cylinder head with the glow plug in it and connecting it up). The only other difference, apart from the new cylinder heads, is that it is now winter and probably about 5ºC in my garage (about 41ºF). If it was a spark plug engine, I would be checking that I had spark and also checking the spark timing but glow plugs don't have a timing, I suppose. I haven't got around to trying to set the carb up, yet, so it could be fuelling poorly, but I have tried cranking it while squirting the fuel into the inlet using a perfume sprayer (the fuel is a model engine fuel which is, I think, a methanol, nitro, oil mix). It should, at least, cough, while doing this; and, last time, back in the summer, it did run with the carb I am using, so I would hope that the fuelling is approximately ok.
I am thinking of trying two further things: a) using EasyStart, as you use for getting car engines started, when they don't want to and b) warming up the whole engine with a blow torch before cranking it and spraying the fuel into the inlet as before.
Has anybody got any suggestions, at all, as to what is going on and why I can't get the thing started, even on the one cylinder? Or any ideas as to what to do next? I am so unfamiliar with glow plug engines that I am a bit lost. The only knowledge I have of glow plugs is of the ones you use in diesel engines to aid cold starting.
Thank you for any help, advice tips or even just comments that you can offer.