Piston clearance issues

jmc25fl

New Member
Sep 29, 2013
26
0
0
Venice Florida
I know this sounds like a idiotic question but a few months back I purchased a grab bag motor from Dax. It was a full 80 CC engine minus the head. I had taken some clutch parts from it, but now I am building as new bike and I have purchased the parts to make the motor complete. I ordered a high compression slant head from dax making sure he knew that I had a motor with the longer stroke. The piston comes up past the top of the head almost 1/8th of a inch. When I put the head on the piston hits and the motor wont turn over. I also noticed that on the down stroke the intake port never clears the top of the piston. Now I am a novice at this but I would think the air/fuel mix would need to make it to the top of the piston so the spark plug can ignite it. Or is that what the transfer ports are for?
Anyway I am hoping someone can point me in the right direction so that I can finish this build.

Also I tried butting three head gaskets on but even with that there is not enough clearance.

Thank you,

James
 

jmc25fl

New Member
Sep 29, 2013
26
0
0
Venice Florida
The strange thing is though is that this piston came with the engine I got from dax. It was a complete engine minus the head. I check a few other engines I have and they have the same type piston.
 

Greg58

Well-Known Member
May 1, 2011
4,084
995
113
62
Newnan,Georgia U.S.A.
Have you contacted Dax to see if they can help you out? Sometimes when buying grab bag or clearance items you find odd and ends that have been put together from several different orders of parts.
 

jmc25fl

New Member
Sep 29, 2013
26
0
0
Venice Florida
I have a call into him now. right now I am making a spacer place for the base of the cylinder as to increase the clearance on top. I give it a 50/50 chance of working, but it gives me something to play with.

Thanks for the tips

James
 

jmc25fl

New Member
Sep 29, 2013
26
0
0
Venice Florida
update I made a really fat base gasket which now gives me enough clearance, but not to much so I am sure my compression is going to be pretty high, but the piston moves freely. Any ideas on anything I might be missing.

Thanks
 

jmc25fl

New Member
Sep 29, 2013
26
0
0
Venice Florida
Thanks for your input. I can't thank you enough. I tried to take enough pictures so that you would have a good idea of the setup of the engine.

The photo's include both ports with the piston all the way up, a pic of the inside of the cylinder with the piston at the bottom, and a few of the gaskets and such. The head gasket is just a stock thin gasket.

Let me know what you think.

James
 

Attachments

Greg58

Well-Known Member
May 1, 2011
4,084
995
113
62
Newnan,Georgia U.S.A.
How does it run? If it runs OK you can break it in and check the compression. Somewhere around 125 psi is what most slant head engines have stock.
 

jmc25fl

New Member
Sep 29, 2013
26
0
0
Venice Florida
125 sounds low. I have a BGF ENGINE and stock it has 160 lbs compression . the motor runs fast. What is normal with a stock head and also with a aftermarket head?

thanks
 

Theon

New Member
Jan 20, 2014
1,440
0
0
FNQ Australia
I think you would be best to check your port timing properly, but it looks to have the wrong piston if you need that much base gasket.