1st thatsdax 38mm stroke "GT5" engine built

mapbike · Apr 17, 2015

Here are some specs that basically tell what the set up in this engine is, lots of put together and tare down and repeat, but I finally wound up with what you see below.

1. head gasket thickness - .040"

2. Rectangular Transfer port Pk80 standard height jug

3. Jug Deck Height reduced .080

4. two different thickness base gaskets one is .020" and the other is .040", total base gasket thickness is 1.6mm

5. Piston has small amount of ramping on exhaust side and the skirt is notched on intake side to reveal an almost completely open port at TDC.

6. Squish clearance between piston and squish ring of Diamond head is 0.70mm

I 'm not sure when I'll have this engine on the bike and running since I'm trying to get the "Taffy Bike" farther along, I justr kept looking at those two dax GT5 type lowers sitting in the box and I want to know how they're gonna perform compared to the 40mm stroke version that I have and really like.

But anyway, below are a couple pix of the dax 38mm stroke I built up last week so when I have a chance I'll be doing an engine swap on one of my bikes to see how this engine is gonna feel as far as vibes go and what the overall power is gonna be.

Sidewinder Jerry · Apr 17, 2015

Nice looking engine.

mapbike · Apr 17, 2015

LR Jerry said:
Nice looking engine.

Thank you sir, just hope its good balanced and a good runner when I get it going.

So far Im partial to the 40mm stroke engines since they have been the smoothest and most powerful I've had so far, but Duane at thatsdax told me this 38mm stroke version will be just as low vibration.

Im curious about it and hope this one runs comfortably at higher rpms, I have two of these lowers I bought from him, this one has a crank that turns very true so it should be low vibration, the other lower I got in the order needs the crank trued up, the wobble in the counterweights is severe.
I'll pull this one apart when I have time or Im thinking about possibly trying to straighten out the wobble without having to take engine completely down, I may have to make a tool for it, but I may try that to see if I can get the wobble out without a comete tare down.

Personally, Im hoping dax will start carrying the good 40mm stroke "GenIV" engines again, in my opinion they have the best crankshafts of all the china girl engines out there.

frank66 · Apr 17, 2015

just making conversation. »how does the inlet look at bdc? does the top ring stay closed ok?

»the gt5a has the bigger mounts wich i like alot. it drops in both my cranbrook and my dirt jumper perfectly.

mapbike · Apr 17, 2015

frank66 said:
just making conversation. »how does the inlet look at bdc? does the top ring stay closed ok?

»the gt5a has the bigger mounts wich i like alot. it drops in both my cranbrook and my dirt jumper perfectly.

No sir, I wouldnt think of having an engine set up where the piston opened the intake at BDC, thats a bad idea for sure....

These engines are the "GT5" geometry engines but not "Skyhawk" engines which use the FM80 marked rods and these from dax have the ZAF80 marked rod, these engines have the standard mounting saddle size front and rear, I have three engines with the wider saddle up front, none are GT5A engines but are actually older engines I bought from BGF back in 2009 and 2010, I like the wide front saddleand wish they were more available in a good well balanced engine.

raising the jug an extra .020" or so wont create any issues with piston opening the intake port @ BDC.

Hope this answers your concern.

frank66 · Apr 17, 2015

so know you think your setup is perfect right? how have you tuned it? you have no idea what the case compression/transfer area is so your just hope to get lucky. its worth a try but you are not an engine specialist or tuner sorry. i look forward to discussion however. good luck bro

mapbike · Apr 17, 2015

frank66 said:
so know you think your setup is perfect right? how have you tuned it? you have no idea what the case compression/transfer area is so your just hope to get lucky. its worth a try but you are not an engine specialist or tuner sorry. i look forward to discussion however. good luck bro

I have never claimed to be a high end tuner or specialist, but I have proven what I do to my engines with the results I get when I run them, how many 50+mph china girl builds have you built?

You tell me how you measure crankcase compression?

measuring transfer area? I know the jugs I use have the largest transfers of any on the market Ive seen.

Show us some pix of your engine builds, port work, case work, piston work, head work, intake work and any of the bikes youve built that pull hills really well and still cruise at 45-50mph on the flat with a 220lb rider.

before you get critical of others you need to prove your superiority with pix and anything else you have that will make anything you say credible.

(I edited this post a little, just got mad and went a little over the top.....lol)

Степан · Apr 19, 2015

Подскажите есть ли у кого чертеж (схема) головки цилиндра?
Есть фрезерный станок, есть желание самому изготовить...
А размеры не знаю...
Извиняюсь, что пишу на Русском

Prompt Does anyone have a drawing (diagram) of the cylinder head?
There milling machine, there is a desire to make ...
But the dimensions do not know ...
I apologize that I write in Russian

mapbike · Apr 19, 2015

Степан said:
Подскажите есть ли у кого чертеж (схема) головки цилиндра?
Есть фрезерный станок, есть желание самому изготовить...
А размеры не знаю...
Извиняюсь, что пишу на Русском

Sorry but we cant read any of this.... if there is some way you can get this into english we could understand what you said here.

FFV8 · Apr 20, 2015

Well, at least he makes sense if you translate it.

He is looking for a drawing or blueprint to make a cylinder head. he has a milling machine.

My reply:

Мы покупаем часть на местном уровне. Там нет чертежи для обработки. Создание головки блока цилиндров не сложно, если у вас есть фрезерный станок .

In english:

We buy the part at the local level . There are no drawings for processing. Creation of the cylinder head is not hard if you have a milling machine .

In Texan:

We just buy the dang things. But I reckon if you have the tools, y'all could just make whatever y'all want.

.

Greg58 · Apr 20, 2015

Frank66 I know Shan pretty well through this forum and have watched his work for over four years, you on the other hand might be trying to show us what you know which sounds like a lot but in the way you are going about it you won't make many friends.

Greg58 · Apr 20, 2015

It's strange that some of the engines that vendors have still have the bushing, all of my he engines I've bought since 2010 have had needle bearings.

mapbike · Apr 20, 2015

FFV8 said:
Well, at least he makes sense if you translate it.

He is looking for a drawing or blueprint to make a cylinder head. he has a milling machine.

My reply:

Мы покупаем часть на местном уровне. Там нет чертежи для обработки. Создание головки блока цилиндров не сложно, если у вас есть фрезерный станок .

In english:

We buy the part at the local level . There are no drawings for processing. Creation of the cylinder head is not hard if you have a milling machine .

In Texan:

We just buy the dang things. But I reckon if you have the tools, y'all could just make whatever y'all want.

.

Hey that's some purdy good Texan ya speaking there, carry on cowboy and evafang....!

mapbike · Apr 20, 2015

Greg58 said:
It's strange that some of the engines that vendors have still have the bushing, all of my he engines I've bought since 2010 have had needle bearings.

Same here Greg, bought my first from BGF in 2009 and several more since then and Ive yet to see one with a bushing other than in pix I've seen on here a few times.

honestly I even think most of the newer chinese wrist pin bearings are plenty good quality, I have a few that I picked up lately that are made identical to the bearings Ive bought from bearingsdirect and I really think they will hold up good for most all applications.

Davezilla · Apr 22, 2015

Greg58 said:
Frank66 I know Shan pretty well through this forum and have watched his work for over four years, you on the other hand might be trying to show us what you know which sounds like a lot but in the way you are going about it you won't make many friends.

I don't think this guy even owns a 66cc bike, but maybe read a few books somewhere along the way and comes in here running his mouth at anyone who actually built anything that can exceed 30mph... There's a huge difference between being able to remember some of Graham Bell or Gordon Jenning's wrritings and actual experience.... None of us have EVER seen a single pic of anything this guy claims to own from any of his previous login names he's used in here...

With that said, I trust Shan's builds 100% and know he's built several really fast bikes so he obviously knows what he's doing...

BTW... that's a really nice looking build and I cant wait to hear about how it runs... I've been curious about these 38mm Dax engines myself...

mapbike · Apr 22, 2015

Davezilla said:
I don't think this guy even owns a 66cc bike, but maybe read a few books somewhere along the way and comes in here running his mouth at anyone who actually built anything that can exceed 30mph... There's a huge difference between being able to remember some of Graham Bell or Gordon Jenning's wrritings and actual experience.... None of us have EVER seen a single pic of anything this guy claims to own from any of his previous login names he's used in here...

With that said, I trust Shan's builds 100% and know he's built several really fast bikes so he obviously knows what he's doing...

BTW... that's a really nice looking build and I cant wait to hear about how it runs... I've been curious about these 38mm Dax engines myself...

Thanks Dave, honestly as far as proper tuning goes you know more about it than I do, I've had some engines that are reall6 good runners, fast, fairly smooth at rpms and will get a bike goind as fast as I want it to go, but Im no 2 stroke specialist at all.

However I have learned many things about tuning on this forum and have applied some of it to my builds, I do need to get me a degree wheel set up so I can have better tuning as far as port timing is concerned for an6 of the 38mm stroke engine especially since they seem to have the most issues in that area with many of the jugs we see.

The dax lower in this thread has a jug that has ports that seem to be ideal for it, exhaust practically wide open at BDC, transfers probably at least 97-98% wide open @ BDC intake port looks good, but like many needs piston notched at least some for the flow to be as good as it can be.

since the 38mm stroke engines do tend to be good reving engines when done right from wha5 Ive heard from others, I did sorta build this one up with ports a tad higher hoping to tap into that higher rpm potential, but I didnt go overboard I dont think.

Proof will be in the pudding when I get this one shoehorned onto a bike and get it running, im considering having this one on the Western Flyer bike now and using that halfbreed engine on my stump jumper project, jus5 have to cross that bridge when I get to it I guess...lol

Thanks for the kind words Dave, Im gonna be leaning on you a bit when I ge5 read6 to set me up a degree wheel since you have that knowledge.

Shan

Davezilla · Apr 22, 2015

Let's just say making a degree wheel and setting it up on an engine is a lot easier than it sounds... I'll take a few pics when I'm at the shop of the GT5 SR I'm working since it's still in that stage of the build, with the wheel, pointer, and dial indicator all still installed and waiting for the day I can spend about an hour or 3 to set the jug hight from the base, set the port events at the degrees I want them to happen at, then finally, set the squish clearance with the head I choose to install at the time...
I got 4 ported jugs sitting on my work counter right now as well as 2 really nice heads... so basically what fits the best on it is what's gonna go on it, then I'll do any final touch ups to the ports before I bolt it on for good...

mapbike · Apr 23, 2015

Davezilla said:
Let's just say making a degree wheel and setting it up on an engine is a lot easier than it sounds... I'll take a few pics when I'm at the shop of the GT5 SR I'm working since it's still in that stage of the build, with the wheel, pointer, and dial indicator all still installed and waiting for the day I can spend about an hour or 3 to set the jug hight from the base, set the port events at the degrees I want them to happen at, then finally, set the squish clearance with the head I choose to install at the time...
I got 4 ported jugs sitting on my work counter right now as well as 2 really nice heads... so basically what fits the best on it is what's gonna go on it, then I'll do any final touch ups to the ports before I bolt it on for good...

i made good mental notes of port timing from a few of your posts and a couple other m3mbers, but its been so long and so much water under the bridge those mental notes turned into paper airplanes and flew away.... well not all of it but a good percentage....lol

I remember Theon or someone suggested using a protractor and I know you said you pri ted something off for your if I actually remember that right, it seems it was said that one of the timing numbers was like 123 or 124 degrees but I dont have it all sorted out in my head now, so some pix and info on the process would be great Dave, good chance it would help others here as well.

I always shoot for getting all the ports as open as possible at BDC and set my jug up to give plenty of open port on the intake when piston is at TDC, I know doing this makes my engines run good but I know that actually getting ports where they need to be will allow one to put the power where they want it and will add rpm potential or can add low down power depending on which way someone wants to go, Im just shooting for that happy medium where I can get a 40mph bike but not loose all my down low.

looking forward to the pic and info Dave and feel free to put it right here in this thread since we have the discussion going on here.

Shan

Davezilla · Apr 23, 2015

Here's a pic of my engine with a degree wheel installed and ready to take measurements... There's no base gasket installed yet so the numbers are pretty far off from what they should be, but by using different thickness base gaskets it allows me to put the top of the exhaust port and transfer ports right where I want them. Raising the jug this way gives a certain degree of control over the transfer and exhaust duration as well as their opening events, but to increaase blowdown would actually require doing some cutting on the exhaust port roof, which may bring us back to too much duration so we need to lower the jug a few thousandths... The transfer duration can be set mainly by raising or lowering the jug with spacers or different gasket thicknesses, then the exhaust can be raised by cutting which will give us the blowdown we're looking for without putting the transfers too far up, but then there's a limit to how high you really want the exhaust roof as it will effect total power if it's up too high, what'll happen is it'll make really strong top end and high rpm power but will begin to take away too much from the bottom end forcing one to need to lower their gearing, which isn't always a bad thing, but if one is looking for a decent cruising speed or top speed and wants to keep the rppm down around 8000 or less then we don't want to raise the exhaust roof more than about 1mm. My last engine had the exhaust roof raised 1mm and I ramped the piston another 1mm for an effective 2mm raised, this was why that engien could rev and make power up in the 10,000 rpm range, but at the same time the bike liked a 40 or 44 tooth rear sprocket for easyt take offs from a dead stop or low speed... More on that later... Here's the pics of my last engine with the 40mm Dax bottom end while I had the degree wheel, pointer, and dial indicator installed... The wheel was printed off the internet then cut out and glued to a plastic sheet then I drilled an 8mm hole in the center, I connect it to the engine with an 8mm bolt that's about 2" long, the wheel is sandwiched between 2 washers and nuts, and a third nut is used as a jam nut to keep the wheel from turning on the crank it's self. The pointer is a similar setup but installed on one of the clutch cover bolt holes with 2 washers, nuts and a jam nut.
The dial indicator at the top is just for establishing TDC accurately since the crank can turn about 3 degrees before the piston moves, so I want to make sure zero on the wheel is actually right in the middle of that movement...

This is the new super rat with the dial indicator installed to find true TDC, I got the wheel on it now but no pics uploaded... I'll post more later...

YesImLDS · Apr 23, 2015

Nonchalant decent size turbo in the back of davezilla's picture....

1st thatsdax 38mm stroke "GT5" engine built

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