my motor kit arrived but possible problems?

Yeshua

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So my 66/80cc flying horse kit arrived all parts were there in good condition for the most part. They sent me a slant head instead of flat head I ordered. My tank had a slight ding and a slightly skewed mounting bolt no rust inside.
Gonna put jb weld at the mounting studs weld to prevent possible leaking. Gonna replace all kit studs with BBR engine studs and replace wheel mount studs. One possible issue is there's a visible gap between head and cylinder body head is not flat and smooth head and cylinder sides have a noticeable combined gap like 1/2mm to 1mm. They're not straight on either side and the original studs are really tight but the gasket isn't flat and definitely not air tight. The gasket is aluminum. The 2 sides don't contact each other either but the studs are tight.My Questions #1 Could it be possible they weren't tightend all the way at factory. #2 how do I remove the unevenness on both sides? Could I sand them flat and smooth? Then use a torque wrench? Please let me know soon. I want to deal with this now rather then later. I'm willing to purchase torque wrench and sanding supply's. Thanks,
Joshua P.S it seems head is backward? Plug hole is facing to back of engine not forward. Which way should it face? Thanks.
 
Plug hole best put whatever way it best fits, mine had to face forward.

For the head issue, glass and fine sandpaper, both the head and the cylinder top, this will help compression a tiny bit but will make for a very nice flush seal, usually the head and cylinder gasket only meet up right around the cylinder hole, it doesn't extend all the way to the headbolts. If you understand what I mean.

Also use a couple extra washers on each headbolt, this prevents the acorn nuts from bottoming out and preventing good torque.

Word of advice for gas tank leaks, don't try to prevent them, it's like trying to fight city hall, takes a lot of work to make it happen so don't try just do it all in one shot. The paint isn't all that gas resistant, putting jb weld on top of it will just let the fuel eat the paint and then it leaks anyways, the jb weld usually cracks too.

Use a tube of something called seal-all, it's a gas and oil resistant sealant, just remove paint from the tank and studs where the sealant will be applied, I used a steady hand and a cut off wheel in a dremel to get the paint of the surrounding area, then a steel wire wheel in the same tool on the stud. Apply liberally and in multiple coats. After all set and done, put a strip of old ture tube between the frame and tank, you can use seal all to glue the tube to the tank if wanted. Tighten the strap on the studs down to the frame LIGHTLY! I emphasize lightly, it only needs to be barely snug on the frame so it can be rather easily rotated by hand on the tube. Get a self tapping sheet metal screw, like used on a license plate, drill a small pilot hole through one strap and right into the bike frame, use the self tapper in that hole, this will prevent the tank from twisting on the frame, while also lessens the stress on the studs, which ultimately causes leaks.
 
So my 66/80cc flying horse kit arrived One possible issue is there's a visible gap between head and cylinder body head is not flat and smooth head and cylinder sides have a noticeable combined gap like 1/2mm to 1mm.
There is a raised sealing lip on the head so there will be a gap.
 
There is a raised sealing lip on the head so there will be a gap.
Oh ok. I saw a gap and thought it was a s**tty head job from factory. That gap is normal? It's just that the gasket is so thin and flimsy doesn't seem to fill the space at all it curlse up at the edges. So that gap will always be there? Seems the stock gasket does nothing at all. But I wouldn't know I've never taken the head off a engine. This is my second motorized bike. First one I had someone build and never looked at the finer details past changing spark plug. This time I have a hobbiest motorized bike builder teach me the build from the ground up and I've read through hundreds of threads on this forum. I'm starting to understand how small engines work now. But any way, to get rid of gap and have better compression I should smooth out head and add thicker gasket? Cuz the stock suds are tight and there's still that gap. Also the BBR tuning studs I'm putting in are hex heads. Should I just put hex adapter on torque wrench or put nuts between stud heads and crush washer to use wrench normally?
 
Plug hole best put whatever way it best fits, mine had to face forward.

For the head issue, glass and fine sandpaper, both the head and the cylinder top, this will help compression a tiny bit but will make for a very nice flush seal, usually the head and cylinder gasket only meet up right around the cylinder hole, it doesn't extend all the way to the headbolts. If you understand what I mean.

Also use a couple extra washers on each headbolt, this prevents the acorn nuts from bottoming out and preventing good torque.

Word of advice for gas tank leaks, don't try to prevent them, it's like trying to fight city hall, takes a lot of work to make it happen so don't try just do it all in one shot. The paint isn't all that gas resistant, putting jb weld on top of it will just let the fuel eat the paint and then it leaks anyways, the jb weld usually cracks too.

Use a tube of something called seal-all, it's a gas and oil resistant sealant, just remove paint from the tank and studs where the sealant will be applied, I used a steady hand and a cut off wheel in a dremel to get the paint of the surrounding area, then a steel wire wheel in the same tool on the stud. Apply liberally and in multiple coats. After all set and done, put a strip of old ture tube between the frame and tank, you can use seal all to glue the tube to the tank if wanted. Tighten the strap on the studs down to the frame LIGHTLY! I emphasize lightly, it only needs to be barely snug on the frame so it can be rather easily rotated by hand on the tube. Get a self tapping sheet metal screw, like used on a license plate, drill a small pilot hole through one strap and right into the bike frame, use the self tapper in that hole, this will prevent the tank from twisting on the frame, while also lessens the stress on the studs, which ultimately causes leaks.
Couldn't I just use a rotery hand sander to spooth out head?
 
DO NOT sand it so much that you remove the sealing ring, you need that
 
I have never, ever sanded one in the 1000 or so I've worked on at my repair shop this last 10 years or so - never had a problem once torqued properly.
 
Couldn't I just use a rotery hand sander to spooth out head?
No!!!
You can never get a flat surface with a sander.

You are seeing problems that aren't there.
The sealing ring on the head is about the same height as
the thickness of the 25 thousands head gasket.
Of course you are going to see a gap.

The top of the cylinders are nice and flat.
The heads can occasionally warp but it is not that common.

You are getting bad advice from a noob.
I have the same experience as crassius, my heads have a machined flat surface.

Leave the cylinder and head unmolested and don't change the studs to allen bolts.
 
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