Ciaran Posted April 14, 2021 Share Posted April 14, 2021 Hi, having high compression issues with my 172 Marco engine on the voloution 2, I had the carb rebuilt, new rings, gaskets etc, as soon as I put the cylinder head on and the spark plug in, it becomes hard to turn over, like really hard! Even when the carb is completely off and the Reed valves are out. It seems like there is pressure is not getting out from the cylinder somewhere, the exhaust ports are all clear and the rings are fitted correctly. If anyone has had a similar problem could you give me some advice please? Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted April 14, 2021 Share Posted April 14, 2021 Some engines have a decompression port for starting; could yours have one and it's plugged up? Quote Link to comment Share on other sites More sharing options...
Ciaran Posted April 15, 2021 Author Share Posted April 15, 2021 I can’t see one, I had the head off etc, the exhaust port is clear along with the other ports within the head Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted April 15, 2021 Share Posted April 15, 2021 I looked online for a manual for your engine, but didn't find one. I found one that *may* be similar at https://prodocs24.com/device/montanari-marco/evolution-130/ Is that the same company? If so, notice part #22, a decompressor valve. Does your engine have anything similar? 1 Quote Link to comment Share on other sites More sharing options...
Blackburn Mark Posted April 15, 2021 Share Posted April 15, 2021 17 minutes ago, Ganbatte said: #22, a decompressor valve. Well spotted.... If Ciaran has one and isn't opening it to start, he owes you a packet of Hobnobs! Quote Link to comment Share on other sites More sharing options...
Blackburn Mark Posted April 15, 2021 Share Posted April 15, 2021 Parajet Volution 2 Pilots Manual Doesn't seem to be any mention of a manual decompression valve... Back to the drawing board Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted April 15, 2021 Share Posted April 15, 2021 Yes, the parajet volution manual doesn't go into much detail about engine service, so I didn't mention that one. He may have to contact parajet to see if they still have a pdf for the volution 2's engine. Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted April 15, 2021 Share Posted April 15, 2021 Oh, and OP: did you clean off all the carbon or other debris, every single speck from the cylinder head? A port of some sort would be tiny, and could be hiding under something that just looks like a smudge. Quote Link to comment Share on other sites More sharing options...
Blackburn Mark Posted April 15, 2021 Share Posted April 15, 2021 7 minutes ago, Ganbatte said: doesn't go into much detail I would expect it would mention the valve in the startup procedure had it had one Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted April 15, 2021 Share Posted April 15, 2021 It wouldn't mention if it were triggered by a starter mechanism in some fashion. Quote Link to comment Share on other sites More sharing options...
Blackburn Mark Posted April 15, 2021 Share Posted April 15, 2021 The one you showed looks like a simple manual open auto shut... Not sure an auto mechanism would earn its keep on a paramotor Quote Link to comment Share on other sites More sharing options...
Ciaran Posted April 15, 2021 Author Share Posted April 15, 2021 Yeah I give it a good clean, it’s like new, the cylinder head and piston. Carb was rebuilt with a genuine walbro kit, new piston rings, new gaskets all round, and still, high compression. It’s in the cylinder sleeve because when the head is of it moves freely, but when I put the head and spark plug on it gets really hard to turn over 🥲 Quote Link to comment Share on other sites More sharing options...
Ciaran Posted April 15, 2021 Author Share Posted April 15, 2021 Also when the exhaust is disconnected from the port, the compression is still high just in case anyone thinks the exhaust is blocked! Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted April 15, 2021 Share Posted April 15, 2021 Then I'd be examining the cylinder walls in excruciating detail, looking for any tiny, unassuming hole. If you do find one, clear it carefully with a bit of wire and maybe solvent, NOT a drill bit. Quote Link to comment Share on other sites More sharing options...
Ciaran Posted April 15, 2021 Author Share Posted April 15, 2021 Will have another look, thanks Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted April 15, 2021 Share Posted April 15, 2021 Have a look here, but i disagree with them about using a drill bit; I strongly recommend against using one. https://www.southwestairsports.com/ppgtechinfo/general/decompression_port/cleaning_decomp_port.htm 1 Quote Link to comment Share on other sites More sharing options...
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