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Post by dubloman on Sept 12, 2017 14:34:39 GMT -5
Hi
I have experience of the GY6 engine and have used big bore kits in the past and will continue to do so moving forward.
The problem I have is this
The above engine we have put a Liyen 150cc block, piston, rings and gudgeon pin (with new clips) on the case.
She fits like a glove and she will turn over (by hand) through a complete rotation without the head and cam (I don't recommend this unless you are experienced) I get no fouling of the piston and she returns back to TDC and the timing mark lines up again
If I put the head on with the cam and bolt everything down, then rotate the engine, I get to BDC and she locks up. If I slacken off the tappets and rotate she still locks up. Do the same again without the rocker assembly on she will rotate no problem.
I am using the head, cam and rocker assembly from the 125 engine and I feel it is either the rocker assembly or the cam that is fouling and causing the lock up
Has anyone got experience with this issue and do I need to change
1. the head
2. the cam
3. the rocker assembly
4. all the above
It's the first time I have come across this problem and it's got me stumped
It looks like the cam won't rotate with the rocker assembly in place so it might need any one of the above but might need them all.
If you have experience of this can you guide me and put me out of my misery and tell me what parts I need (part numbers would be good)
Thanks
Dave
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Post by 90GTVert on Sept 13, 2017 6:26:39 GMT -5
I get to BDC and she locks up. If I slacken off the tappets and rotate she still locks up. Do the same again without the rocker assembly on she will rotate no problem. Is this a typo and you meant TDC? If it's locking up at or near TDC and removing the rockers lets it rotate, I'd suspect interference with the valves. |
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Post by dubloman on Sept 13, 2017 7:04:52 GMT -5
No, it was not a typo
TDC is where the piston is at it's highest point
BDC is where the piston is at it's lowest point
With respect, I do appreciate the feedback, but.... I do know what I am talking about as I have years of experience in car engines as well as MBT's, I was attached to the REME when in the military.
I agree that the top end is fouling but need to know if it is the rocker assembly or the cam, or if there is something that I have missed. With the 125cc engine it turns over perfectly but put the big bore kit on the cam or rotating stops when the piston turns half of a rotation at BDC. Even with the tappets fully slackened off it still locks up
I hope this clears up the misunderstanding and I appreciate your reply but the problem is a weird one and I have never come across this issue and even speaking to racing supply tech's they agree it is weird. I am trying to find the answer.................I know all gy6's are not the same
Cheers
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Post by 90GTVert on Sept 13, 2017 7:22:23 GMT -5
I mean no insult. I make plenty of typos and that's a common problem. It's easiest for me to get the most obvious thoughts out of the way first. With that said, here's another that may be too simple for you...
Are you securing it with the cylinder nuts when it is turning freely? My thought is if it's only stopping at BDC when you've got the whole top end installed (I'm assuming you're securing it with the nuts at that point), perhaps there's a clearance issue with the piston and the crank at BDC. A very close fit may allow it to pass by if just holding the cylinder by hand to see if it rotates, and then stop when torqued down. Sorry if this is also too basic. Don't take it as an insult. I've seen some weird pistons before in setups that I could swap a different kit on and never have trouble, but for some reason the skirt would be long on one and it would bump the crank and have to be trimmed. Anyway, the easy check for that would be to bolt it down without the cam in place and then see what happens.
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