52mm stroker build.

[islandscrub]

Aloha!

I am planning my first GY6 4T build and pieced together a kit to go with a bike I don't even own yet Just looking for advice/experiences with any of these parts.

So far I've got the SMM 52mm kit, probably going to 'unshroud' the valves on it, or have it done.

64? Rockers

Bigger 24mm intake boot

Glixal A9 cam

Carb is up in the air, most guys do the 24mm here.

Still don't own the stroker crank.

I also heard the A9 cam may not be much better than stock, should I bother with it?

[ratdog]

IMHO, a striker is a lot of work for a small gain.the biggest issue is how do you compensate for the longer stroke and your piston height? If you just throw it in with a normal piston and stock height jug, the piston top is like a mil and a half higher. Do you take your piston to a machine shop and have a mill and a half taken off the top? The easy way would be to kake a base spacer undere the jug, but now your timing chain is to short. The striker crank is really a crank from a different motor that happens to fit in the GY6 cases. I don’t know of any source for a shorter rod, or a piston with shorter pin to top spacing. IMHO your opening up a whole can of worms for very little gain.

The “A9” cam is not really a preformance cam. It actuly has less duration then the stock cam and many of the examples I have measured had slightly less lift. The only thing they have going for them is that they are cheap and many people say well they are so cheap, what the heck! My suggestion is put the bike back together with the stock cam, then later swap in the A9 and see if it’s any improvement. I recently took the A9 cam out of one of the bikes I have done BBK kits on, and there was no decrease in preformance. Same top speed, same 0 to 40 times.

[islandscrub]

We apparently have a stroker crank available with a shorter rod. Someone tried to explain how having a shorter rod keeps it at the stock heights but I can never visualize it properly in my head.

I will try and leave out the cam initially and see how it goes. How does the stock cam and 64 rockers interact? Valves are still a little bit of a mystery to me.

Any suggestions on carb size? I have a feeling the 20mil would be enough since the opening in the head is only 20, and the opening in the intake boot is only 22. I figure its cheap enough to get a 20 and a 24mil carb and try both.

[ratdog]

OK, the information I had was that all the striker cranks were the same. I guess that was wrong.

The biggest issue on choice of carb is the RPM range you want your motor to run in. When we build hot hod engines, we move the Peak up the RPM range. Now others things being equal,you get more hp with more RPMs. And th at requires bigger carbs. You have an engine that gives you about 3 hp at 7500 RPM. Now you can build a big engine that still peaks around 7500 rpm, or you can build an engine that make more hp at higher RPMs. More RPMs means more wear and less engine life. Frankly, you could build a big displacement engine that ran just great at 7500 rpms on a 18 mm carb. Or you can go to a bigger carb and run at higher RPMs which will give you more speed. Just remember that everything else in the engine is designed to handle 3 hp.you build a 10 hp engine that peaks at 12,500 rpm and it may not last long.

The other thing you should look at is if the carb has an acceleratior pump. It’s my understanding that a lot or the 24 mm carbs don’t, but frankly I have not checked into them..

So, a 20 mm may be a great choice to get good power without going up the RPM range too much. That said, I use a 22 mm c arb on my 82cc build and I would guess my hp peak is around 10,500. The engine will pull 12,500 with ease. But frankly, this thing is just a hobby for me, so if I end up with an engine in a thousand pieces tomarrow, I’ll just say “damn that was fun!”. Every weekend I may spend more on my drag race stuff then I have on this whole buil.

Your head dictates what rocker arms you use. I’m sure you wouldn’t attempt this with a stock head, so no doubt you will get a bigbore head that includes the valves and rocker arms

[proy]

island scrub do you have a link to the stroker crank with a shorter rod or any information on it?