View Full Version : GY-6 engines

herman pahls
02-09-2015, 05:18 PM
Hello Forum
My 5 year grandson needs more power for his mini dune buggy when in the sand dunes.
It tops out at 20mph and climbs small dunes quit well.
It is currently powered by a 50cc 2 stroke Honda scooter engine.
The electric start and CVT drive system are a big PLUS.
I am considering the 150cc GY-6 engine that many import buggies are powered by.
These engines are readily available on e bay but most are not complete with the exhaust,intake,carb, ignition...
Also the drive system to a sprocket would be needed.

1...Are these engines reliable?
2...Where are you GY-6 owners sourcing your engine parts?
3...How much HP at what RPM do these engines put out?
4...Are they water or air cooled?
5...Do some have upright cylinders to reduce the over all length?


02-09-2015, 06:02 PM
Hi Herman;
the gy6s are reliable, air cooled, though a few also have oil coolers and most problem issues come down to wiring connections, electrical components and dirty or fouled carbs because of ethanol mix fuel.

They make 10-12 hp stock, rev up to 8-9k and are pretty rugged. The weights in the variator (drive pulley) can be changed as can the clutch (driven pulley) main and secondary springs to bias the power curve to bottom or top end performance. There are also plug-n-play rev-limited CDIs for young drivers.

Parts are plentiful, most hit e-bay or use the preferred vendors who advertise on the couple main forums websites that deal primarily with the 150 mini buggies.

When buying an engine, there are a couple of types that are oddball.
157qmj "short" case is the most common buggy engine, can be had with internal or external reverse gearbox.

There is a 1P57qmj that's a bit different internally --it has a unique crank setup that prevents using a stroker kit.

If buying used, there are some older ones with 2-bolt valve covers that you can't get big bore kits or performance cams for. Common type is a 4-bolt valve cover.

110 cc versions can be found with upright jugs, most 125s - 150s are in-line, 250s are upright and mostly watercooled. Linhai might have an upright 150, but i don't think so.

For mounting, you'd need a bigger swingam than what you've got . BMI Karts bought the "remains" of Yerf Dog aka Flxible Flyer corp when it went under including all parts etc. Along with that they got complete karts and kart parts from the Yerf "Spiderbox" 3206-4206, 4209 models that had been recalled because of front ball joint failures. They still have for sale complete rear swingarms with engines installed from the recalled karts. Its a common style 4-bolt valve cover Howhit engine, electric start, but no reverse. There are reverse kits that can be added to them though. They sell the backhalfs both tested and untested, as they're all used, though i've not heard of anyone having problems with one. howhit is a very good brand.


herman pahls
02-09-2015, 08:14 PM
Thanks for referring me to BMI karts.
I just got off the phone with them and they are the source I would need if I go with the GY-6.
The big plus with BMI is that you actually get to talk to someone which is not the case with most e bay sales.
Before I read your reply I found short case GY-6's on Ebay by T-motorsports.com for $236. plus $60 shipping for new engines.
These engines are complete minus the muffler and the drive sprocket that is splined to fit the out put shaft.
BMI has those parts including the CVT belts which was another concern.
The only issue with the BMI Yerf Dog used engine and cradle is the shipping cost.
The sales person estimated $300 in shipping.
If I get the T-motorsports engine I will need to buy the muffler and the drive sprocket and air filter which would come with the BMI engine and help offset part of the shipping.
The T motorsports GY-6 also comes with a kick starter which could come in handy with a dead battery if the ignition will run on the magneto.

Thanks for answering my previous questions.
I have some more if you have the time.

1... What is the total length of a short case GY-6 engine if you have one near by to measure?
2... Are the GY-6 shortcase engines standardized to the point that if I bought a new one from T motorsports would the exhaust, splined drive sprocket, ignition parts, etc... interchange with BMI parts?
3... About how much do these engines weigh?
4... This engine will be used mostly in the high drag environment of the sand dunes.
The mini buggy will weigh approx. 250 pounds and the driver approx. 60 pounds.
How well should I expect the drive belt to hold up assuming it is geared properly?
5... Is the engine air cooling adequate.
6... The Yerf Dogs were geared 13-31 for 20 inch tall rear tires.
Any idea what speed that translates into for hard surfaces?
I am trying to get an idea how to gear this project.
7... Any idea what the gear reduction is on the out put?
8... How tolerable noise wise is the stock Yerf Dog exhaust?

Thanks again and my Grand kids will appreciate you helping me out.

02-09-2015, 09:21 PM
Not sure if this is what your talking about or not, but I have one waiting to go in a buggy.

Theres a vid In there too, to get an idea of the power.


herman pahls
02-09-2015, 09:59 PM
Hi Bullnerd
All the GY-6's I have seen have horizontal cylinder placement so the engine unfortunately gets quite long.
Your engine is ideal with vertical cylinder.
I goggled Carter Interceptor GTR 250 hoping to find a source of engines but just saw the complete buggies.
Looks like a great engine package but may be too much for my 5 year old for now

02-09-2015, 10:53 PM
GY6s weigh about 65-70 pounds. Just shipped a "P" type out today. 74 pounds boxed--plywood reinforced box and a couple extra parts.

A rev-limited CDI would keep the speed down until he's ready for it. about $20 and a 2 minute swap.

At the weights you mention, you'll be fine as will the belt--as long as you pay attention to the cvt air intake and make sure it's not blocked.
Noise level isn't too bad ... shot thru my jvc video cam, ignore the metal thrashing noise, that's a bronze bushed steel chain tensioner chewing itself to death ... Not a howhit, but they all sound pretty similar.


Again you can tune the CVT for the riding style/terrain and add a 39T rear sprocket.
Internal gear ratios/final output vary, IIRC, the howhits in the yerfs are 13/41--before you buy, find out the trans/output ratio.

You'd want to set it up for staying down low longer at a cost of top speed, you'd end up with a 28-30 mph kart. 22" tires are about as tall as the gy6 can handle. there are several yerfs that run the sand and do pretty well in it. Yerfs out fo the box were some of the fastest top speed minis becasue they were light and geared well. about 32 mph stock on the flats and they're in the 300 opund loaded range. It takes a ton of work to get a 150cc mini past the 35 mph mark, 40 is about it and that's rare.

length is 26 inches

Other, and possibly better suited option might be to go with a 5 to 6 hp industrial engine and comet convertor. you can get some with electric start option. My daughter's ride started out as a 50 cc mini that i modded larger overall and went that route ...

The engine bull has is a CN or CF Moto 250 (two similar types of the cvt type 250) Search under that and you'll find most of the info you need.

herman pahls
02-10-2015, 03:09 AM
More great info.
Are you a dealer for these engines since you shipped one recently?
What is a P type. I only know of short and long case.
The video makes me wonder if you still have grass in your yard.
What do IIRC and howhits refer to.
It seems like a stretch from my experience dealing with the GY-6 sellers for them to know that there is internal gearing let alone the ratio.
Do you feel the 6.5 HP clone engines with a Comet CVT can compete with the 150cc GY-6 in power?
The Predator 212 has 6.5 HP but only revs to 3600rpm in stock form.
I googled the engine bull cf moto 250 CVT.
I like that it has a vertical cylinder but they are not a available as GY-6's from what I found.

02-10-2015, 03:27 AM
not a dealer by any stretch, messed with them for a few years and just sold off the last one i had with the exception of the one in the latest project. the "P" type i mentioned earlier, is a short case with a slightly different crankshaft design, internal reverse.

Still trying to regrow the front yard, have pretty much created a full on 1/8th mile dirt oval in the backyard :D

IIRC mean "if I recall correctly" ... Howhit is one of the better manufacturers, used in the yerfs, bajas, Tomberlin and other brands.

predators to gy6 are apples and oranges. low rev/ bottom end grunt vs higher rpm and more mid-upper range power band. In one way, I think the gy6 is a better choice for you given sand riding, but at the same time, it may be too much for the chassis. ...

Now i've been going on the assumption that the chassis is something like the hammerhead mini shark, mudhead or torpedo kiddie size buggy ... ???

02-10-2015, 10:07 AM
I haven't read the whole thread so forgive me if this has been said already. The price of used china buggies are pretty cheap, why not just get a buggy with a 150? It would probably cost less once you've sold the smaller buggy.

herman pahls
02-10-2015, 05:17 PM
You make a very good point which I had not considered.
Buying Ala Carte always costs way more than the full meal deal.
I enjoy building from the ground up so I can incorporate items like a differential so they turn sharper and fully independent suspension and mini steering racks.
I will shop for a used GY-6 powered buggy and either modify the chassis or use the components in a new build.
Thanks for the ideas.

02-10-2015, 05:23 PM
I don't see them for sale often but there are 250cc china buggies with independent suspension.

02-11-2015, 09:52 AM
Gear Boxes (http://www.motopartsmax.com/index.php/main_page/index/cPath/21_28)

herman pahls
04-08-2015, 05:23 AM
I decided that there were too many unknowns regarding my knowledge of the GY-6 engines so I decided to re power my 4 year old grandsons fully suspended mini sand car with a Harbor Freight Predator 212 6.5 HP engine.
I wanted to replace the Honda Scooter 50cc 2 stroke engine with a 4 stroke with more power.
I spent $100 on the engine, $190 for the GTC torque convertor and another $100 for a mechanical disk brake caliper, sprockets, chain and other tidbits.
Today was the day for my grandson to do the test drive on the dunes here in Southern Oregon and I was very pleased with the results.
The roll cage only fits 4-7 year old kids with a helmet on so adults can not drive it without sitting on the roll cage.
I was afraid that using a lawnmower engine would be a 50 year step backward.
To my surprise the top speed went from 20 to 30 mph with the new stock engine and it climbed dunes that he could not before with ease.
He misses the electric start but I do not miss the 2 stroke issues.
With this engine and with 10 to 70 tooth sprocket gearing from the torque convertor and 20" tall tires this thing accelerates and climbs way better than I expected.
I am ready for suggestions from those of you that have "hot rodded" these Predator 212 engines what you did to get more power and where did you buy the parts from.

04-08-2015, 11:11 AM
What no video? lol

herman pahls
04-09-2015, 05:07 AM
Tell me how to post a photo or video to this forum and I will make it happen.
All I know how to do is text or Email photos/videos from my I phone.
Thanks Herman

04-09-2015, 09:39 AM
For youtube videos I just copy the address bar and post it here.

04-23-2015, 07:00 PM
Just bought a used 150cc Chinese ATV with a GY6 style of engine. Pretty neat package. Mine has reverse too.