New cylinder head available on Ebay!

Hey Greg.
Yeah you are right. I'll be putting up a decked cylinder jug for sale on eBay later today. I just took off .025" off the top face. I'll be offering others soon that will have .065" taken off the top for those who want to use two bottom gaskets under the cylinder.

It is a little different if you have a GT-5 motor; the first step I would offer for that engine would be .060", and then, If you want to run with two bottom gaskets you could get one with .100" taken off.

With these numbers, I'm assuming the average bottom gasket thickness is about .040" after being compressed. I'm also assuming that the crankshaft is not terribly distorted.

Thanks



-Fred

Fuji Moto said:

where do i find the right kind of motor to work with your head? the one where the piston goes as high as the top of the jug?

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Hi Fuji Moto!
Well, it a bit of a long answer, but I'll try not to blab too much!
As far as the 66/80 cc motors that I have experience with are two types; I don't know all of the particulars for the GT-5SR "super rat" engine because I can't seem to find any. There are a bunch of engines being sold on eBay by companies like "Lucky Early Bird" and "Boy Go Fast". Those engines are the lowest priced units that I know of. These engines will have the highest compression due to the particular piston and connecting rod they use. just make sure it has 8MM studs for the cylinder! Those engines have a older transfer port design.

If you want the best engine, read further about the GT-5 motor:

The newer GT-5 engine is available from Gasbike.net. That engine is a little more money, but it has a better cylinder design. The GT-5 engine uses a "odd ball" connecting rod and piston and requires more material to be faced off the cylinder in order to achieve maximum compression.

All these engines suffer from a disappointing problem of having distorted crankshafts. I suspect the only new engines which are free of this problem is the GT-5SR "super rat" models, which I can't find.

There is hope for these reject engines!
Gasbike.net offers a replacement crankshaft assembly, which I'm told is the crankshaft used on the super rat. I've purchased two of them already, and so far, they are Straight!

So, anyway, I told you this would be long-winded one!

Soon I'll be offering all of the different cylinders to go with the head.
The other thing I can offer is machine shop service, so you can send me your cranks and cylinders for reworking. Cylinder decking is $5.00 and crankshaft straightening and truing is $25.00, not including shipping.

Once you have one of these "reject" engines reworked like this, it turns into a pretty reliable motor. You can also readily get the puller for taking the sprocket and bevel gears off the shafts.



Hope your not too confused!!! Thanks
-Fred

I'm back again! Ha!
Alright, here is the eBay link for the decked cylinder jug to be used with the high compression head. This particular cylinder will work for the non GT-5 engine with 8MM studs and ONE bottom gasket.

http://www.ebay.com/itm/130727243747?item=130727243747&viewitem=&vxp=mtr#ht_747wt_1110



-Fred

Alright Fuji Moto, very cool!

Yes, it is very confusing, but I think you've got it!

The engines you can get on ebay are cheaper, and right out of the box, have higher compression, but if you want maximum horsepower, I think the GT-5 motor is the way to go because it has a better cylinder design.

Now, if you want maximum horsepower, I would tune for high rpms, so running two bottom gaskets would be a good idea. So, if you use all of the gear from the GT-5 motor, including the crankshaft, I would say, get it straightened and trued. In this case, you would want to use a GT-5 cylinder with .100" taken off the top.

The other scenario would be to use the replacement crank they sell on Gasbike.net. That will require a different piston than what comes with the GT-5 motor. In this case, you would need to use a GT-5 cylinder with .065" taken off the top.

I have some pistons for both style engines in stock. I will put those up on ebay soon as well; probably later today. These pistons have two small bevels on the top to allow better flow out of the transfer ports.

Sounds like you are on the road to having one sick engine!!!!



-Fred

No doubt!
You do know that there are reed valve assemblies that are available for these engines, right? Venice motor bikes has them I think. And there is another company.. I think their name is Arrow motor bikes. They ought to help a great deal for low and mid range power, but I think they would cause a restriction to flow at high RPM. That is based on what I've read, not from experience.


-Fred

Fuji Moto said:

i think it would be easier to get the engine kit and crank from gasbike, and the beveled piston, decked jug and nice head from you, and just assemble everything, but are you sure that crank they sell separate is going to be nice and true and balanced, or would i be better off taking the one that comes in the engine and get you or the average joe at the shop across town to balance and true it?

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About the replacement cranks they sell at Gasbike.net?
Well, I've purchased two of them and they were both really straight and true, so I think your chances of success with that is pretty good. One of the cranks I got from them has to be fixed because the little 8 X 1.0 thread for the magnet got messed up when they threaded it. That's how they are, they will sell you reject parts!



-Fred

Fuji Moto said:

im not too sure how to check if it is true and balanced properly i guess i could look into it, but not to into buying tools and equipment when all i need is one and plus im cheap, also, what exactly is needed to split the case and change out crank? pullers etc also, if im buying a different modified cylinder jug then why do you recommend going for the engine that comes with a particular cylinder, unless the bottom end is also different? im still alittle confused i guess but you guys are very helpful anyway!

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Well, these are the things you'll have to work out. Unfortunately in order to deal with the bent crankshafts that are in about every engine available, you are forced to do engine work, unless you purchase already reworked engines. I'll probably try to sell those again in the near future. There is a bit of labor to teardown and rebuild, so one of my engines will cost about $300.00. That might be the best way to go if you don't want to do the engine work. If you don't deal with the crankshaft, and you want to rev high, I'm afraid the engine life won't be very good.

You can buy a puller tool for taking the engine apart. All the other tools are pretty basic. I think a few sellers call it a "screw tool"; kind of a lame name for it.

And if you were to manage to do the engine work, the idea would be to send me the cylinder and crank for reworking. Then I'd send it back to you and you would put it all together. If you had extra parts for what ever reason, you could put them on the shelf for later use.

Well, anyway food for thought, eh?
I'm sure you'll figure out a plan. Good luck on that!


-Fred

ivan H said:

Hi guys, I recentl added the Rock Solid Engines reeds (au$65) & havent lost top end, tho havent ported 4 higher rpm as I'm running a shiftkit so have gone 4 increased low/mid torque. I did notice a gain in this area without aditional mods 2 compliment the reeds, tho it wasnt stock when I added them. I will soon b doing the additional mods so the intake is thru 180 degrees. Cheers

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Hey Ivan. You are running some reed valves. Really? no loss at high RPM? wow, that's better than I would have expected! Are you worried about breaking the chain using one of those shift kits?


-Fred