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Engine piston wont cycle
hey all, i need your help, i just replaced the connecting rod on my super tigre 75 engine. I put on the cylinder head on the engine on and bolted it down and tried to turn the engine over but couldnt, the pistion was hitting the top on the cylinder head when the shaft was turned..what is the problem here and how do i fix it? i've taken 2 engines apart and never had this happen [ul][*] [*] [*]
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RE: Engine piston wont cycle
Could eithet be you left out the head shim, or the conrod is hitting the case.
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RE: Engine piston wont cycle
Are you sure it was actually hitting or is it just really good compression? If you take the head off and turn the crank, does the piston come out the top of the shaft? If it does, then it is indeed hitting the head. If it is, then I have no idea. My suggestion would be to double check that you have everything in the right position and maybe pull it out and put it back in just to be sure you did it right.
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RE: Engine piston wont cycle
yeah its definatly making contact with the cylinder head, i may have to disassmble and try it again, the head shim was in place too
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RE: Engine piston wont cycle
ORIGINAL: blhollo2 yeah its definatly making contact with the cylinder head, i may have to disassmble and try it again, the head shim was in place too Do you still have the old conrod? If so, check the length between the two. Maybe they sent you the wrong one. |
RE: Engine piston wont cycle
Is there a raised spot (dome or ridge) on the piston that is hitting the head? If so the piston OR the head could be mis-aligned.
Second question - does the eng fully rotate with the head off? Just noticed part about new connecting rod. Most likely wrong length. |
RE: Engine piston wont cycle
thanks! it does fully rotate with the head off, the connection is the spec rod for this engine, i think it might be misaligned but the engine lacks of any way to know if it not
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RE: Engine piston wont cycle
Is the piston top completely flat? or other?
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RE: Engine piston wont cycle
Flat
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RE: Engine piston wont cycle
OK, so you have a G-75 as shown on pg `14 of http://manuals.hobbico.com/sup/supz0099-manual.pdf ? And you have the gasket shown as item 22 in the drawing on pg 14?
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RE: Engine piston wont cycle
If your answer is YES, I'm going to recommend that you go to the RCU SuperTiger forum for dedicated advice. http://www.rcuniverse.com/forum/forumid_163/tt.htm
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RE: Engine piston wont cycle
my bet is the backplate is improperly installed.
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RE: Engine piston wont cycle
If it goes around when the head is off, how could the back plate have ANYTHING to do with it????
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RE: Engine piston wont cycle
ORIGINAL: blhollo2 Flat Con-rod is wrong length. glow plug is fouling the cylinder head. Test by removing plug and trying to turn over. Piston gudgeon pin is fouling the transfer ports; cylinder liner is not aligned correctly, gudgeon pin is not secured properly. Con rod is not symmetrical. It has a front and a back. The front has a rounded machining of the big end bearing web to clear the crank pin support. The back side does not have it and fouls the support preventing the crank from rotating fully if assembled the wrong way round. Piston ring upside down and is fouling the lip in the top of the cylinder liner that comes with wear. Debris in the intake venturi fouling the crankshaft intake slot. Debris in the bearings. A fold in the space-time continuum that manifests as an inability to rotate Super Tigre cranks. (OK maybe not, just been watching Stargate SG-1) |
RE: Engine piston wont cycle
ORIGINAL: psuguru ORIGINAL: blhollo2 Flat Con-rod is wrong length.Possible glow plug is fouling the cylinder head. Test by removing plug and trying to turn over.Possible but not likely. Piston gudgeon pin is fouling the transfer ports; cylinder liner is not aligned correctly, gudgeon pin is not secured properly.What the heck is a "gudgeon"? If what I think - not likely. Con rod is not symmetrical. It has a front and a back. The front has a rounded machining of the big end bearing web to clear the crank pin support. The back side does not have it and fouls the support preventing the crank from rotating fully if assembled the wrong way round.Disproved by the fact that it DOES go around without the head. Piston ring upside down and is fouling the lip in the top of the cylinder liner that comes with wear.Did not remove/change ring. OK before-OK now. Debris in the intake venturi fouling the crankshaft intake slot.Not relevent, it goes around without head. Debris in the bearings.Nope, not this either. A fold in the space-time continuum that manifests as an inability to rotate Super Tigre cranks. (OK maybe not, just been watching Stargate SG-1) Most likely so far.:D |
RE: Engine piston wont cycle
ORIGINAL: psuguru A fold in the space-time continuum that manifests as an inability to rotate Super Tigre cranks. (OK maybe not, just been watching Stargate SG-1) seems like a stupid question but did you switch to a different plug? |
RE: Engine piston wont cycle
ORIGINAL: moron88 ORIGINAL: psuguru A fold in the space-time continuum that manifests as an inability to rotate Super Tigre cranks. (OK maybe not, just been watching Stargate SG-1) seems like a stupid question but did you switch to a different plug? |
RE: Engine piston wont cycle
bruce, what year did you graduate?
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RE: Engine piston wont cycle
ST like to make their engines with the piston coming within around .010" from the top of the liner and the head sitting flat on the liner. Put a straight edge on top of the liner and turn the piston to TDC and see if it lifts the straight edge. There should of course be a very small gap between the piston and straight edge. If the piston lifts it off the liner then GaryHarris nailed it with the wrong rod. There's no way a glow plug can extend far enough to foul the piston in an engine of that size. If the rod is the wrong length then the top of the piston will also sit slightly higher than the bottom of the exhaust port with the piston at BDC.
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RE: Engine piston wont cycle
ORIGINAL: moron88 bruce, what year did you graduate? |
RE: Engine piston wont cycle
If the only thing you changed was the conrod, look there.
I live by the "if it's screwed up now, what did I touch last?" principle. Jack |
RE: Engine piston wont cycle
ORIGINAL: bruce88123 [What the heck is a "gudgeon"? If I remember my "Cannoneering 101", a gudgeon is a twisty bit in a cannon. |
RE: Engine piston wont cycle
ORIGINAL: bruce88123 If it goes around when the head is off, how could the back plate have ANYTHING to do with it???? I had a smaller super tiger (i think it was a car engine actually) lock up because the backplate was on upside down when i put it back together. It would turn it and it acted like it was hitting the head. I actually thought it was hitting the head. Cameron |
RE: Engine piston wont cycle
ORIGINAL: Cambo ORIGINAL: bruce88123 If it goes around when the head is off, how could the back plate have ANYTHING to do with it???? I had a smaller super tiger (i think it was a car engine actually) lock up because the backplate was on upside down when i put it back together. It would turn it and it acted like it was hitting the head. I actually thought it was hitting the head. Cameron |
RE: Engine piston wont cycle
Is it fixed yet?
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