no compression

HT60CC

New Member
Jul 23, 2008
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Slough, England
I haven't got any compression! I recently replaced my head studs and I torqued down the head to about 15ft-lbs and I used gasket sealant. I don't think that this is the problem as when I turn it over bubbles go through oil around the spark plug. Is it the washer on the spark plug causing the trouble?
 

jasonh

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Jun 23, 2008
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if you're leaking air around the spark plug, then that's your problem. New plug and washer will probably fix that, as long as you properly torque the plug.

When I got my new cdi and mag on, I forgot that I had just hand-tightened the plug. Was running like crap till I saw that thing dancing around, lol.
 

Norman

LORD VADER Moderator
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Jan 16, 2008
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did you pull the head and cylinder clear off to repalce the head studs? you might have broken a ring when you put it back together.did you use a new base gasket the same thickness and the old one? Is the head gasket the some thickness as the old one and what gasket sealant did you use?
 

HT60CC

New Member
Jul 23, 2008
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Slough, England
No I didn't remove the cylinder sleeve. I used the same gasket and just applied a thin coating of sealent. I was told that the gasket sealent is suitable for head gaskets, it has a picture of a head gasket on the front of the tube. it's hylomar universal blue Hylomar
I don't think it's sold in the USA, or maybe it is under a different brand.

I'm going to have a closer look tommorow when I can get a better look.

cheers
 

Norman

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Jan 16, 2008
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I use aliminum silver spray paint for the head gasket sealant if I use anything on the head gasket. I do try and lap the head on wet/dry sandpaper .320 grit on a sheet of glass to get the sealing areas nice and unifrom I also lap the top of the cylinder as they are not finished at all on the one I've taken apart. the laping helps to make a ture and flat surface. the head gasket is soft aliminum and they sometimes are a one time use item but can be reused in a pinch with the spray paint trick I coat the gasket on both side with the paint and either let it dry or if I'm in a hurry I'll install it wet. Just make sure the can says that the main ingredants is aluminim the cheaper the paint the better.
for torquing down the head bolts/nuts I start at 40 inchlbs in a cross pattern then 80 inchlbs in a cross pattern them 120 inchlbs in a cross pattern run it for a day or two then recheck it at 120 inchlbs.
 

zendiecut

New Member
Apr 4, 2009
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Boston suburb
I'm having trouble with an engine I installed on a Rat Fink chopper. I took the plug out, looks black and wet. I then rode it without the plug in and put my thumb over the plug hole. If I push fairly hard, my thumb won't even get blown off the hole. What gives? I know if you do it to a 4 stroke, your fingure will difinately get blow off the hole.

The bike runs like crap and I can't get to WOT. Just bogs down. Tried new jets from Dellorto Direct and none of them helped. Adjusted the needle, put a "O" ring on the intake. I did turn the cylinder, head and piston around to put the exhaust out the back. I checked everything out and it didn't look like that would be a problem. Any ideas?

Here is some answers for you.
did you match up the base gasket?
wet and oily plug indicates overly rich you will need to go smaller on the main jet stock is usually .70mm most all of mine are reworked and are .65mm.
is your engine new? as it wears in your compression should increase. You are using both rings on the piston one guy tried to use only one and that isn't a good idea.
use a compression guage to acturaly measure the compression and use it with the throttle wide open.
Norman
 
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Cabinfever1977

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Mar 23, 2009
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Upstate,NY
ht60cc did you tighten the plug,not just handtight.

zendiecut your problem maybe that you turned the jug and piston around,it will run but the bottom block is made to accept intake from one side. im just guessing at this one.
 

zendiecut

New Member
Apr 4, 2009
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Boston suburb
Thanks. But I studied this ting pretty good before I spun it. The cylinder walls and ports on the bottom sides are symetric. The gas comes into the underside of the piston at the top of the stroke and is compressed in the crankcase when the piston comes down. The gas then goes up from the crankcase through the side channels (one on each side) and into the cylinder through the ports on the sides of the cylinder walls.

Unless there are reed valves inside the crankcase (I highly doubt it), I don't see how it matters what direction the head is in. I just read that these angines only have a compression ratio of about 6 or 7:1. That's pretty small. Much smaller than say a lawn mowers, which will blow your thumb right off the plug hole.

But I'll consider turning it back around and see if it does matter. Thanks.
 

Norman

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Zendicut
You will need to grind the base and cylinder to match up for a good match if your going to run the cylinder backwards the base gasket will also need to be matched to this set up. I did the backwards cylinder a while back and if I would of left it that way the base and cylinder would need to be matched I did make a special gasket for it.
the motorized bicycle engine(china engine) doesn't know if the cylinder/ head set up is on forwards or backwards.
The leaking spark plug could be due to a poor machining of the spark plug hole seating area of the spark plug that might need to be either replaced with a different head or reworked.
Norman
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
Here's a question... Is the piston skirt the same length on the front & back??? Maybe you have to flip the piston too to get the same port timing???

I just re-read.... you DID turn the piston... sorry.
Check the base gasket again, maybe there's a air leak from the transfer ports not matching?
 
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city of angels

New Member
May 24, 2009
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tucson az
this happen to me and i know this might sound funny but the reason it was'nt firing it because their was water in the gas my mechanic figure out with a small blow torch he soak a paper towel and the try to lit it and nothing happens the n he got new gas and sure enough the bike fire right up
 

zendiecut

New Member
Apr 4, 2009
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Boston suburb
Read carefully. I inspected the piston (turned it anyway), inspected the gasket (it is symmetric), inspected the base (it is symmetric also), inspected the ports on the inside sides (they are for letting the mix into the top of the cylinder and they're symmetric as well).

I found a blog about a guy having the same problem. Guess what? Bad magneto. I will check the readings on the mag and CDI per info on another blog and let you all know. These mags a known for failure problems.
 

zendiecut

New Member
Apr 4, 2009
25
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Boston suburb
Ok guys. I'll try this again. And I'm not getting pissy with you. I don't have a problem with the spark plug seat. All I said was that when I put my thumb over the hole and peddle with the clutch out, that it won't blow my thumb off the hole. The compression seems to be low. I read another blog that said the compression ratio of these engines is 6 or 7 to 1(6:1 or 7:1).

I have no leaks anywhere. And Norman is right. There is a difference between the top of the crankcase and the bottom of the cylinder head. But no leaks. The intake (side wall) ports don't match exactly. Could be restricling fuel flow if the mating creates smaller holes, which it does.

I flipped it back around, and destroyed the gasket in doing so. Does anyone have a template I can use to create a new gasket? 50CC engine. I can buy one, but they takes forever to get parts for any of these things.

Thanks - Jack
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
Use the base of the cylinder as a template... C'mon bro, be creative!! :)
You can buy a roll of gasket material at most auto parts stores.
 
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