GT5 small port cylinder pics

I have several eyebrow/cateye cylinders and have them running on three of my bikes, the best pulling engine I have that pulls hard from low down all the way the 45+mph has a cylider jug with large rectangular transfers and larger intake and exhaust.

Yes the engines with the cat eye transfers run fine but none of my engines running that setup will rev like the engines with the rectangular port engines will, you just cant get as high of performance from an engine that only opens about half the ports at BDC, they dont allow as much air fuel mix into the cylinder and this is what limits them, however for the average engine that is restricted by a stock exhaust or just not set up for higher rpm, the slanted cat eye shaped transfers do a great job, they wont work as well for high rpm builds though, or at least that has been my personal experience.

Both of my fastest and highest reving engines have been set up with the rectangular port jugs, m6 other engines with basically the same mods wont hold a candle to them in the potential revs department, they do run good and yes they have good grunt power but they wont wind up nearly as high on the top end.

They all have a good use depending on what sorta build someone wants, if high rpm is xesired the larger rectangular transfers are best, the other jugs work great for everything else for me.

Now being Im no pro at any of this I have to say that some that have more knowledge on all of this than I do can probably get more out of their cat eye port engines, but with the simple port cleaning and piston ramping Ive done with mine, the smaller ports dont measure up to the rectangular port jugs.

frank66 said:

yea. same here. the best porting i have done is by spinning a chaincaw file with my fingers as a rotory tool for the finish work. it takes off all micro burs. its like a miracle on aluminum cylinders.

how long till you try one out? are you waiting for something?

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since i work full time and I been building another bike the last couple of weeks my time has been really slim, but I got the new build running today after fighting through a couple a failures, dang mag went out, replaced it and then a brand new CDI went out, since my first build in 2009 these were the first mag and cdi Ive had go bad on me, but its running great now, engine is a GT5 platform with a shaved GT5 jug, Fred piston, good port work and thats about it other than a well tuned NT carb, do a fairly good job of port matching the header pipe of a stock exhaust and polishing it real good.

anyway, I plan to get one of the dax, lowers together asap, I have to get a piston prepared, a jug shaved down and the ports leaned up, it takes me several hours in a fay or part of two days to get all that done and then get the engine together.

I wish I had more time but I just have to do what I can when I can and then I have things to do around the homestead as well.... oh the life of a country fella that also works full time...lol!

maniac57 said:

Not to threadjack here but Map do you have any info on this weird jug of mine?
I've tried it one three different cases and it always ends up too short. Piston sticks out and hits head without 4 base gaskets...
Is this the haflbreed jug?

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Hmmmm....

well, the half breed engines use the same jug height as the pk80 40mm stroke engine or at least the one I have did.

if its a GT5 jug and you're placing it on either a half breed lower or a pk80 lower the piston will stick up out on it like that.

have you been running the lower that you have that jug on in the pic?

The reason I ask is because if you put a low pin pk80 type piston on the rod of a GT5 engine it will make the piston come up out of the ylinder like that also.

Do you know for sure what kind of lower you have there?

Only two things I can think of that will cause this is a plow pin piston on a long GT5 rod or a GT5 jug on a low pin piston in a 40mm stroke lower.

Where did you get that cylinder jug?

maniac57 said:

It's got the standard ZAE80 rod is all I know about bottom end.
I have a GenV 40mm stroke so I know better than to mix pistons...
Always ends up about 1/8th too short to work without a spacer under the jug. Exhaust port shows same 1/8th mismatch if you slide it down.
Are there THREE piston pin locations or is this from a short rod engine?

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ZAE80 Rod?

I have the two dax GT5 lowers that have the ZAF80 rod and the Half Breed has a ZAE50 rod, but I'm not familiar with a ZAE80.

Are the engines with the ZAE80 rod 40mm stroke engines?

I'm thinking it has to be a jug for a GT5 geometry engine or a jug that someone else shaved way down form some reason.

Where did you get that cylinder?

There has to be a simple explanation for what it is unless it has been shaved by someone.

frank66 said:

the flying horse is the third piston. i think its the tallest one. um what is your cylinder height? also measure piston from crown edge to pin top edge and crossreference with jnm's descriptions.

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The older Flying Horse engine I have has the same pin height as the 40mm stroke Pk80, but it has a larger diameter wrist pin than the Pk80 or the GT5.

I know nothing much about these new engines that are being called Flying Horse, I do know that they aren't the original geometry Flying Horse engines from what I have read and that the name was purchased and just attached to these newer engines since it was a name people recognized.

Bike Berry list a different piston for there "Flying Horse" engines than what is listed for the GT5, looks like the pin height is the same as the GT5 but the Flying Horse engine has a larger Diameter wrist pin.

pic is directly off of Bike Berry's web site.

frank66 said:

jnm has pictures with measurements. i wont quote them because one of the numbers seemed wrong concerning a piston pin but maybe im not familiar.

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I looked on JNM and didnt see where they had info on the pistons, where is it located on their site?

I went to look there after you mentioned it but I guess I'm missing it somehow.

my GT5 jug is shorter than the pk80 jugs, you have to take quite a bit more off the deck of a pk80 jug to run it on a GT5 lower.

the rod is longer in the GT5 but the lower rod journal is positioned lower than it is on a 40mm stroke crank and the wrist pin is higher in the piston, time all is said and done this set up requires a shorter jug than the 40mm stroke engine.

cannonball2 said:

Point well made I forgot to take into account the hi/lo piston pins. So M57 has to have the wrong piston?
The 114 rod will use the high pin. If one used a low pin then it would be above the deck.
Trying to come to a conclusion on the several combos and the proper assembly of them.

How is the GT5 running?

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kinda what Im thinking also.

The GT5 is running excellent, Im lacking a little on the very bottom end grunt which is mainly do I think to the fact I put a stock exhaust pipe on it, but for some reason it really comes alive in the mid to upper rpm range even with that stock type exhaust, I did do as good a job as possible to port match the pipe to the head to help flow some, so I know that helping the revs.

This particular GT5 has minimal vibes, very smooth overall and the higher it revs the smoother it gets, that is one thing Im really liking about it so far, gonna have to try a different exhaust on it though just to see if the pipe on it now is whats hurting the low down power a little.

Im liking how this engine is running so far and hoping both of the GT5 dax engines I have will also purr like this one does when I get them running.