02 zuma just rebuilt top end and feels like low compression

[palehorse]

Should I be able to turn the engine over slowly by hand and only feel slight compression or should it be tight as heck as it compresses?
It seems very low when turning by hand. Not like a chainsaw or weed whacker. I only used gaskets on head and cylinder should I also use honda bond or other HT silicone?

[aeroxbud]

It's probably because you are doing it slowly. Try taking the plug out. Then putting your thumb over the hole while kicking it over. The compression should force your thumb off.

[Zino]

if you have the spark plug out
You should turn it by hand to check the function of the piston and rings so its not binding .
you should hear a puff of air come from the spark plug hole and feel a small amount of compression

Once you put the spark plug in you will feel quite a bit of compression and you will need to kick it over to get it to go through a full cycle .

I always use a sealant like Honda bond to rebuild these engines

[palehorse]

The kickstarter and plate are not on yet. So I am turning it over by hand. With the plug out and thumb over hole I feel a moderate amount of pressure but not near enough to force my thumb off. There is no carb or muffler on right now either. Should I honda-bond the paper gaskets on clylinder, reed cage and copper gasket on head?

[bacon]

Did you happen to check squish or ring gap before final assembly? What top end did you put on? Did you lube everything up with 2-stroke oil when you assembled?

After my top end rebuild I was able to slowly turn the engine over by hand but you could definitely feel the pressure. It would slowly turn over as the pressure escaped around the piston/ring. I checked compression with a gauge afterwards and it was north of 140psi if I remember correctly. I set my squish to somewhere around .85mm but that required some work. Had I just thrown the gaskets on that came with the kit it would have been quite a bit higher. I used no base gasket (yamabond) and machined the head down so I could use a head gasket and get my target squish.

[palehorse]

Yeah I havent checked anything. I bought a slightly used cylinder, head and piston from fleabay as the stock oem parts are discontinued. I didnt want to run a BB kit as the crank has 26k miles on it and I thought it might break it. I just wanted a stock oem 50cc head, piston and cylinder. The one I got looks good and is matching parts from one guys bike that did put a BB kit on his and sold me his old stuff. Said it had 1200 miles on it and low carbon on piston makes me think that is true. I oiled all parts for assembly. I have been working on my own stuff for 50 years. I guess I could pull the base gasket and craank it over without. I dont need it to see if compression jumps up. Can I honda-bond the head gasket too instead of the beefy copper thing to bring compression up more? Just comparing it to my 50cc stihl chainsaw that will hold the saws weight by the rope on the compression stroke. Its tight!

How hard was it to turn by hand and were you turning the fan over at the crank or using the kickstarter?

[bacon]

Check your squish before you pull the cylinder or head off again. Easy to do with some solder through the spark plug hole. You can use the copper gasket spray on the head, but I dont think the case sealant like hondabond or yamabond will hold up the temp and pressure at the head. Just pulling the base gasket out might do what you need it to do. You could also likely get by with copper spray and no head gasket (assuming the surfaces are in good shape). Just a note of caution that pulling gaskets out can interfere with port lineup but if youre not going for high performance that's probably not a huge deal.

I was turning mine over with the fan/flyhweel so I had some mechanical advantage to it. Before going to the BBK my stock head was low on compression (80psi) and that turned over much easier. Stock had two rings, my BBK has a single ring.

[palehorse]

May 20, 2024 20:57:19 GMT -5 bacon said:

Check your squish before you pull the cylinder or head off again. Easy to do with some solder through the spark plug hole. You can use the copper gasket spray on the head, but I dont think the case sealant like hondabond or yamabond will hold up the temp and pressure at the head. Just pulling the base gasket out might do what you need it to do. You could also likely get by with copper spray and no head gasket (assuming the surfaces are in good shape). Just a note of caution that pulling gaskets out can interfere with port lineup but if youre not going for high performance that's probably not a huge deal.

I was turning mine over with the fan/flyhweel so I had some mechanical advantage to it. Before going to the BBK my stock head was low on compression (80psi) and that turned over much easier. Stock had two rings, my BBK has a single ring.

I pulled the base gasket and the compression jumped to what feels like normal. I am going to find some solder and do a test before assembly. The old cylinder I pulled off had a gasket. But its junk now. Ill post back after squishing. How long to let honda bond dry at base? Is 3 days good?

[palehorse]

Ok it looks like its .69mm at the edge of the cylinder. The stock head has a weird shape. Its like a groove between the plug hole and the edge of the cylinder wall so its high low and then high again. Where can I get the thin aluminum head and base gaskets?

[bacon]

Some kits like Athena come with them. What brand is yours? You could make one if you're crafty. I think they say .7mm is the min. You're real close to that - you could let her buck and see what happens. And yes, 3 days is plenty for Hondabond or similar

[palehorse]

Its just a stock oem 50cc head piston and cyl. Do I honda bond the oem stock copper head gasket. Which way does the little raised groove go?

[aeroxbud]

The raised groove goes up.
No need to use Honda bond on it.

[palehorse]

OK------------> There is a GOD and he is shining his love down on my piston and cylinder, whooooyaaaaa!.

Just ran a compression test after decking the head by hand .010 and the compression is 130. The squish is good too. I decked the head by hand on a flat piece of glass. I would start with 200, 600, 800, 1000, 2000. I sanded off .003 at a time rotating the head and moving the head in a wide circle on the paper. I would caliper the surface to the head bolt to make sure it didnt start leaning one way or the other. In the end it was between .010-.012 removed.

On a sad note, once I plugged in all the wires to the motor and hooked up new battery the only thing that worked was the horn. No headlights, no starter, no dash lights, no running lights, nothing. The main round battery fuse is good. Is there a fuse box somewhere? I cannot find it.

Ideas why no power except horn? Battery is new and charged. I used it to hot wire the starter to crank for compression.

[aeroxbud]

That does sound like the main fuse. I would check the fuse with a multimeter or replace it. Sometimes they can look good but still not work.

[palehorse]

Jun 12, 2024 3:35:07 GMT -5 aeroxbud said:

That does sound like the main fuse. I would check the fuse with a multimeter or replace it. Sometimes they can look good but still not work.

I pulled the fuse and checked with a meter, its good. Do the headlights not come on until its running? Where is the starter relay located? Is there a fuse panel or more fuses? Is there a wiring diagram that shows where everything is located, not a schematic.