I'm building a 79cc Predator engine build

Donavan321 · Jan 13, 2014

I have recently purchased a 79cc predator engine. I'm planning on using the mounting plate from the 4 stroke grubee kit to mount it to a cruiser frame. I will probably use the EZ gearbox, if anyone has any pointers to make this build as CHEAP as possible, I'm listening. Otherwise I can suffer spending lots of money. Lynn of custommotoredbicycles has successfully built these for those of you who know her. I'm building mine up slowly piece by piece I obtain. I've got the engine on hold for me. I should have that within a few weeks or less. If anyone has any useful parts,gearboxes, etc that will aid me in my build. I've got paypal. I'm really excited! I ran the engine and it's smooth as buttter and hardly vibrates, it will be awesome! Pictures will be posted as I progress! To those of you who have built these... get a hold of me with pictures and pointers thanks!

GearNut · Jan 13, 2014

While there are many threads concerning the 79cc Preddy, These ones came to mind:
http://motorbicycling.com/showthread.php?t=49398
http://motorbicycling.com/showthread.php?t=50892
http://motorbicycling.com/showthread.php?t=47494
This one is a 99cc, but the engines are nearly identical:
http://motorbicycling.com/showthread.php?t=44847
This thread may be of interest to you:
http://motorbicycling.com/showthread.php?t=52555

There are more, just use the search function at the top of the page.

Donavan321 · Jan 13, 2014

GearNut said:
While there are many threads concerning the 79cc Preddy, These ones came to mind:
http://motorbicycling.com/showthread.php?t=49398
http://motorbicycling.com/showthread.php?t=50892
http://motorbicycling.com/showthread.php?t=47494
This one is a 99cc, but the engines are nearly identical:
http://motorbicycling.com/showthread.php?t=44847
This thread may be of interest to you:
http://motorbicycling.com/showthread.php?t=52555

There are more, just use the search function at the top of the page.

Thanks! I have read some of those, Thanks, again.

birdmannn101 · Jan 14, 2014

I have about $695 invested in my build but I splurged.

$ 80 New Huffy Nel Lusso
$ 80 New 79cc engine
$ 80 Sturmey Archer front brake/dynamo hub
$ 90 To have someone lace the hub with #11 spokes
$ 30 Engine mount
$ 45 Sproket adapter
$ 37 For 44 tooth sproket that fits the adapter
$135 Jackshaft
$ 12 Throttle linkage
$ 12 Short shaft crank
$ 64 Exhaust
$ 30 Centrifugal clutch

and I am a very happy camper

BarryT · Jan 14, 2014

Donavan,
If you're looking for cheap, I built this engine mount out of 1/4" steel plate and welded 4 female ends of muffler clamps (top & bottom) to the plate around the cutouts.
http://motorbicycling.com/album.php?albumid=1491&pictureid=8872

Donavan321 · Jan 14, 2014

BarryT said:
Donavan,
If you're looking for cheap, I built this engine mount out of 1/4" steel plate and welded 4 female ends of muffler clamps (top & bottom) to the plate around the cutouts.
http://motorbicycling.com/album.php?albumid=1491&pictureid=8872

Thanks! Although the mounting plate isn't an issue at the moment for me.. I'm more concerned with the clutch. I was going to get an EZ Q-Matic, but they're terribly expensive. I'd like something cheap. I know some guys have found decent clutches that were under $100. That's a great bike you've got there! I was going to do one on a cruiser myself.

GearNut · Jan 14, 2014

Yes, the EZ Q-Matic is pricy, but it is worth every penny.
I love mine! Strong and dependable and other than lubricating the clutch bushing after each outing (very easy to do BTW) is has been maintenance free.

runnermike · Jan 14, 2014

BarryT said:
Donavan,
If you're looking for cheap, I built this engine mount out of 1/4" steel plate and welded 4 female ends of muffler clamps (top & bottom) to the plate around the cutouts.
http://motorbicycling.com/album.php?albumid=1491&pictureid=8872

Do you have a closer image of the mounting plate and the female ends of the muffler clamps??

Donavan321 · Jan 15, 2014

Also thought about mounting this predator behind...making one of those "pusher bike trailer rigs" any good ideas for that method?

KCvale · Jan 15, 2014

Donavan321 said:
Also thought about mounting this predator behind...making one of those "pusher bike trailer rigs" any good ideas for that method?

Unless you want to remove motor power completely a lot and always ride straight just say no to a pusher trailer drive as the last thing you want is the trailer shoving your back tire sideways and jackknifing you into a wreck when you try to power from a dead stop around a 90 degree corner.

I have only built one as most of my customers like my 49cc 3-speed shifters but it turned out nice.

29" single speed Macargi Fatal Love bike.
1.2 gallon Wizzer tank.
79cc Pred.
Q-matic drive.
Mounts, sprocket, throttle,etc from a leftover 49cc 4-stroke bike kit that was jackshafted.
Exhaust made from a cut and re-welded 2-stroke cat pipe.

I didn't have a 49cc 3-speed shifter to run head to head with the 79cc direct drive but both rock, the big difference is all the customizing and extra parts you need like a throttle system, fuel supply, exhaust and mounts to make the Pred go.

Donavan321 · Jan 15, 2014

KCvale said:
Unless you want to remove motor power completely a lot and always ride straight just say no to a pusher trailer drive as the last thing you want is the trailer shoving your back tire sideways and jackknifing you into a wreck when you try to power from a dead stop around a 90 degree corner.

I have only built one as most of my customers like my 49cc 3-speed shifters but it turned out nice.

29" single speed Macargi Fatal Love bike.
1.2 gallon Wizzer tank.
79cc Pred.
Q-matic drive.
Mounts, sprocket, throttle,etc from a leftover 49cc 4-stroke bike kit that was jackshafted.
Exhaust made from a cut and re-welded 2-stroke cat pipe.

I didn't have a 49cc 3-speed shifter to run head to head with the 79cc direct drive but both rock, the big difference is all the customizing and extra parts you need like a throttle system, fuel supply, exhaust and mounts to make the Pred go.

Yeah, I was thinking the same thing too. I can't afford a Q-matic at the moment and probably won't be able to anytime soon. I was thinking of using a jackshaft setup that would power a "direct" drive to the rear wheel. I'm not sure yet, I'm exploring "transmission" options. Several people on the forum here use that AGK jackshaft kit which is powered by a centrifugal clutch. I've been exchanging PM's with another member on here. Found an eBay listing of a centrifugal clutch for $27 free shipping. I've been hoping I could find a torque converter that would fit the shaft..besides the Qmatic, not sure yet. I've built a lot Happytime builds, and I've had bad luck with the friction drive..I think chain drive/frame mount is the way to go.

KCvale · Jan 15, 2014

Donavan321 said:
Yeah, I was thinking the same thing too. I can't afford a Q-matic at the moment and probably won't be able to anytime soon. I was thinking of using a jackshaft setup that would power a "direct" drive to the rear wheel. I'm not sure yet, I'm exploring "transmission" options.

Just some important notes and my opinion from my 1st hand experience with 40+ wheel gear shifter builds with 2 and 4 stroke engines...

Your first consideration is what parts you have on hand and your fabrication skills.

I build higher end custom motorized bicycles for a living and one thing I know is I find it better to get a 'box of parts' as a kit with everything that is known to work well together and go from there kind of like a box of lego's or tinker toys.

In short a 2HP 49cc 4-stroke HS kit from gasbike.net with the nice new Grubee 4G cent clutch transfer case and everything you need to build a direct drive is ~$350, $50 less than just a Q-matic transfer case for any Pred bare engine with no parts to mount it or make it function.

Then there is the Sick Bikes 4-stroke 'box of parts' kit for $200 which leaves you spending $150 more than just the Pred and Q but not only do you have everything you need to use your bikes back wheel gears with the engine you have a bunch of spare 4-stroke engine mounting hardware and drive system parts like the back sprocket and rag joint, mounting plate, and hardware for future use which as a builder I will use eventually like I did for the Pred build.

So far it is a toss up in my mind for pros and cons as which drive is best as I like both but again it all comes down to is your time, skills, budget and parts on hand.

For example on these two 4-stroke builds I had all the the leftover parts which the SBP kit which replaces most everything but the needed parts like the fuel and control system parts.

In short about $500 total parts for a legal in most states 4-stroke shifter with nothing else to buy or have to fab, especially the mounting, exhaust and throttle stuff for a Pred.

Again in my case with a bunch of extra parts from most everything 'parts in a box' kits and build a lot of bikes I am a in different category as most builders, but if you want a nice reliable 4-stroke that will run with a 79cc Pred but be able to ride at 5 MPH to ~38 MPH it's a hard system to beat in my build book.

Donavan321 · Jan 15, 2014

KCvale said:
Just some important notes and my opinion from my 1st hand experience with 40+ wheel gear shifter builds with 2 and 4 stroke engines...

Your first consideration is what parts you have on hand and your fabrication skills.

I build higher end custom motorized bicycles for a living and one thing I know is I find it better to get a 'box of parts' as a kit with everything that is known to work well together and go from there kind of like a box of lego's or tinker toys.

In short a 2HP 49cc 4-stroke HS kit from gasbike.net with the nice new Grubee 4G cent clutch transfer case and everything you need to build a direct drive is ~$350, $50 less than just a Q-matic transfer case for any Pred bare engine with no parts to mount it or make it function.

Then there is the Sick Bikes 4-stroke 'box of parts' kit for $200 which leaves you spending $150 more than just the Pred and Q but not only do you have everything you need to use your bikes back wheel gears with the engine you have a bunch of spare 4-stroke engine mounting hardware and drive system parts like the back sprocket and rag joint, mounting plate, and hardware for future use which as a builder I will use eventually like I did for the Pred build.

So far it is a toss up in my mind for pros and cons as which drive is best as I like both but again it all comes down to is your time, skills, budget and parts on hand.

For example on these two 4-stroke builds I had all the the leftover parts which the SBP kit which replaces most everything but the needed parts like the fuel and control system parts.

In short about $500 total parts for a legal in most states 4-stroke shifter with nothing else to buy or have to fab, especially the mounting, exhaust and throttle stuff for a Pred.

Again in my case with a bunch of extra parts from most everything 'parts in a box' kits and build a lot of bikes I am a in different category as most builders, but if you want a nice reliable 4-stroke that will run with a 79cc Pred but be able to ride at 5 MPH to ~38 MPH it's a hard system to beat in my build book.

Yeah, I was thinking about that as well. Just buying a 4 stroke kit and getting the whole works all in one box, compared to buying individual parts. I don't have access to a welder, or many other fabrication tools. Also, another member had mentioned the 79cc needs a clutch with 5/8th bore size. Not sure if the 79 and 99cc have the same shaft. Can you send me a link to the 4 stroke "box of parts for $200"? can't find that. I have a lot of two stroke parts laying around, I'll for sure need a throttle handle/grip assembly and cable(15 bucks..big whoop) and a gas tank(also easy to get) thanks!

Donavan321 · Jan 15, 2014

Donavan321 said:
Yeah, I was thinking about that as well. Just buying a 4 stroke kit and getting the whole works all in one box, compared to buying individual parts. I don't have access to a welder, or many other fabrication tools. Also, another member had mentioned the 79cc needs a clutch with 5/8th bore size. Not sure if the 79 and 99cc have the same shaft. Can you send me a link to the 4 stroke "box of parts for $200"? can't find that. I have a lot of two stroke parts laying around, I'll for sure need a throttle handle/grip assembly and cable(15 bucks..big whoop) and a gas tank(also easy to get) thanks!

I also already have the predator engine....

KCvale · Jan 15, 2014

Donavan321 said:
Yeah, I was thinking about that as well. Just buying a 4 stroke kit and getting the whole works all in one box, compared to buying individual parts. I don't have access to a welder, or many other fabrication tools. Also, another member had mentioned the 79cc needs a clutch with 5/8th bore size. Not sure if the 79 and 99cc have the same shaft. Can you send me a link to the 4 stroke "box of parts for $200"? can't find that. I have a lot of two stroke parts laying around, I'll for sure need a throttle handle/grip assembly and cable(15 bucks..big whoop) and a gas tank(also easy to get) thanks!

The big difference you are missing in this whole actual engine output shaft rotation the difference in output RPM ratio between the actual engine RPM rotation and the output shaft RPM.

On a typical 2-stroke on the right side under the clutch cover you will see a big difference in the reducing gear to lower the gear ratio before it gets to your output drive sprocket and it's own manual clutch system build in.

4-stroke engines have no internal reduction gearing or clutch, the output is the actual crank shaft of the engines RPM itself, hence why they need some kind of external gear reduction and clutch system

In short you need some kind of big gear ratio reduction between actual raw engine RPM and it's back wheel drive drive srocket RPM and of course you can do that with just a cent clutch small front sprocket and a giant back wheel sprocket or pulley like the Wizzer's used but hey, tech has improved since the '60s.

My major point is you can't just put a a cent clutch on a 79cc pred and then use a regular 2-stroke kit back sprocket on the back and expect it to work.
Sure a 4-stroke with 4+ gear reduction will work great on a go kart with 5" wheels and a sprocket the same but that is a far cry from trying to spin a 26" wheel with direct engine shaft RPM unless the rear sprocket is about the same 26" diameter.

Keep those factors in mind as you proceed.

Donavan321 · Jan 15, 2014

KCvale said:
The big difference you are missing in this whole actual engine output shaft rotation the difference in output RPM ratio between the actual engine RPM rotation and the output shaft RPM.

On a typical 2-stroke on the right side under the clutch cover you will see a big difference in the reducing gear to lower the gear ratio before it gets to your output drive sprocket and it's own manual clutch system build in.

4-stroke engines have no internal reduction gearing or clutch, the output is the actual crank shaft of the engines RPM itself, hence why they need some kind of external gear reduction and clutch system

In short you need some kind of big gear ratio reduction between actual raw engine RPM and it's back wheel drive drive srocket RPM and of course you can do that with just a cent clutch small front sprocket and a giant back wheel sprocket or pulley like the Wizzer's used but hey, tech has improved since the '60s.

My major point is you can't just put a a cent clutch on a 79cc pred and then use a regular 2-stroke kit back sprocket on the back and expect it to work.
Sure a 4-stroke with 4+ gear reduction will work great on a go kart with 5" wheels and a sprocket the same but that is a far cry from trying to spin a 26" wheel with direct engine shaft RPM unless the rear sprocket is about the same 26" diameter.

Keep those factors in mind as you proceed.

Yeah, I've always known that. This build is a little more complicated because the happytime engines are SPECIFICALLY designed for bicycles. This predator engine is meant for multiple applications. I'll need a cent clutch FOR SURE...and I'll have to have a chain running from the clutch to a jackshaft and the jack shaft will drive the chain that drives the rear wheel. I've driven go karts, never built one. I've repaired 4 stroke engines but have never installed or removed cent clutches. I've been spending the last few months looking into this project and I think I'm pretty well prepared, I'm just double checking that the parts I buy will fit. I don't want to be wasting money and returning things dealing with unnecessary hassle. I was looking for a torque converter...it would do the same thing the jack shaft would...which is powering the rear wheel. Also, belt drive is quieter than a chain. I've seen several online but none of them say they fit 5/8 shafts. I've seen people use torque converters on the predator 212cc engines that were one ebay for $100. I don't know if the shafts on all of the predator engines are the same. I'm prepared to go the jack shaft route if I must.

KCvale · Jan 16, 2014

Donavan321 said:
I was looking for a torque converter...it would do the same thing the jack shaft would...which is powering the rear wheel. Also, belt drive is quieter than a chain. I've seen several online but none of them say they fit 5/8 shafts. I've seen people use torque converters on the predator 212cc engines that were one ebay for $100. I don't know if the shafts on all of the predator engines are the same. I'm prepared to go the jack shaft route if I must.

Yep, I bought this TC for a 212 Pred I was going to build but went with a 79 Pred and not only would it not bolt on it was HUGE and unlike a JS robs you of about .5 HP.
http://gokartsusa.com/Comet-TAV2-GTC-Torque-Converter-Predator.aspx

Sure it 'kind of' shifts by the front and rear pulley's changing size a little by RPM and drag but nothing like rear back wheel gears. All this is great for a really big engine but suck for a little 79cc

That was almost $300 with all the stuff you need delivered and sold it for like 1/2 what I paid and got a Q-matic for the 79 Pred.

The Q-matic is self contained, has everything you need including the Cent clutch, works great (and belt drive with it's on internal belt tensioner) and much thinner than any TC.

You need to decide which one of the things you mention you want, trying to design something cheap without wasting time and money on what you try, or just buy something that will bolt right on a work perfect but no gearing.

Or again as I mentioned forget the 79 Pred and go a 49 HS and SBP shift kit.

Donavan321 · Jan 16, 2014

KCvale said:
Yep, I bought this TC for a 212 Pred I was going to build but went with a 79 Pred and not only would it not bolt on it was HUGE and unlike a JS robs you of about .5 HP.
http://gokartsusa.com/Comet-TAV2-GTC-Torque-Converter-Predator.aspx

Sure it 'kind of' shifts by the front and rear pulley's changing size a little by RPM and drag but nothing like rear back wheel gears. All this is great for a really big engine but suck for a little 79cc

That was almost $300 with all the stuff you need delivered and sold it for like 1/2 what I paid and got a Q-matic for the 79 Pred.

The Q-matic is self contained, has everything you need including the Cent clutch, works great (and belt drive with it's on internal belt tensioner) and much thinner than any TC.

You need to decide which one of the things you mention you want, trying to design something cheap without wasting time and money on what you try, or just buy something that will bolt right on a work perfect but no gearing.

Or again as I mentioned forget the 79 Pred and go a 49 HS and SBP shift kit.

Well, I'm going to stick with the 79cc pred build for now. I'm thinking I'll buy a cent clutch(watching one on eBay that will fit and work) and rig up a jackshaft and then once I have the funds, do away with all of that and invest into a Qmatic( I know, I know, they're worth every penny!) I'm building up my kit first and THEN bike shopping/experimenting. I found some good deals online for some bikes. What size bolts fit in the mounts on the pred? ....to mount the engine to a plate? Fine thread or coarse? Also, bolt size that goes into the crankshaft to keep the clutch on. Thanks!

ocho ninja · Jan 18, 2014

Here is my preddy build. Started off with a 79cc and later swapped it for a 99cc with a thinner head gasket for bumped compression.
http://motorbicycling.com/showthread.php?t=45405

I got alot of technical info and some parts from AGK
http://www.affordablegokarts.com/99cc-predator.php

Good luck with your build, these are great little engines for motor bicycles

Donavan321 · Jan 18, 2014

ocho ninja said:
Here is my preddy build. Started off with a 79cc and later swapped it for a 99cc with a thinner head gasket for bumped compression.
http://motorbicycling.com/showthread.php?t=45405

I got alot of technical info and some parts from AGK
http://www.affordablegokarts.com/99cc-predator.php

Good luck with your build, these are great little engines for motor bicycles

Awesome! Thanks, my clutch came in the mail today, I've got it bolted on and it seems to work good, I can hold it with my hand and the engine will idle without trying to take my hand off(it spins when I let go, probably because there's no chain to stop it from spinning. I'd like to hook the engine up to a HT gas tank. However, I've noticed it has really skinny fuel line, would I have to use a different carburetor? If so which one? Lynn of custommotoredbicycles uses the stock carb and what looks like 1/4" fuel line hooking onto the nipple. Maybe the 5/16(the bike kit line) will fit if I used a hose clamp? Let me know thanks!

I'm building a 79cc Predator engine build

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