Jump to content

American Sportworks 650 2wd engine swap, to Predator 670

Recommended Posts

A few pictures (so far) of the engine work - eventually I will share wiring info and other details (if anyone is interested?)  should anyone else ever need to swap an engine in one of these. The replacement engine is a Harbor freight $750 special 670cc,  (lawn mower/industrial type lump) with a few minor upgrades. Should have it back together soon, bolted in. The cold weather slows me down! 





Link to comment
Share on other sites

Getting it back together.  Engine final mockup and assembly done.  Needed to bump the engine to the passenger side about 1/2" to line the CVT up inline with the original location on the old engine.  The 670 has a longer crank snout where the pulley seats. Just waiting on some parts for the carb (this setup uses a 1.5mm needle and seat for use with a pulse pump), and the moto carb to stock throttle arm cable,- should be here tomorrow - and we are ready to fire. Starter cranks, all wired up. I only ended up with a kill wire for now,  (blue wire from UTV, black/red wire on the motor) , and the starter (white wire ), along with the fused hot wires.  Will hook up the oil sending unit from the old engine so I have the oil light. 




  • Like 1
Link to comment
Share on other sites

  • 2 weeks later...

Update on the swap.  Since getting the new engine spun up, and dialing in the Mikuni, we have been putting this buggy to use!  After a good snow storm, it proved to be handy to have to go clear broken branches and fallen trees in the area. and on our property.  I could tell right away though something wasn't quite right with the CVT, it would 'shift out' and the motor would just wind out (as in 5K+ RPM)  too high in other words at an anemic 20 MPH tops. Once all the work was done I learned all about this CVT setup.  Here is what I learned, and this should apply to all CVTech PWB50/80 type CVT setups for reference.

I did the pen mark on the driver(primary) sheave to see what was up with the primary clutch pully, and it was only climbing out with an inch or more of the pen mark left. So I ordered a new Kevlar belt, turns out the original belt was worn about .032" or more, and the new belt being wider will climb higher up the sheave making it more efficient at least.  While I was at it I decided to pull the driver pully off, and clean it up, document the spring, blocks, weight, and make sure everything worked - I suspected it was jamming up on the stationary sheave binding the sheave stroke.  But I came to discover these clutches have a "Stroke limiter" ring, that stops the sheave stroke about .250" short of the full stroke.  Since CVTech specs these CVT's with a shift ratio of 6.97:1 - (3:1 - .43:1 ratio range), with the limiter ring in there it limits the clutch to a 4:1 shift ratio = 3:1 - .75:1  or so depending on belt, spring, etc.   So after reading the service information and some trial and error, mock fitting the belt to the sheaves and checking the belt position to full shift out, I removed the limiter to allow the full shift ratio of 7:1.  To make a long story short - not only does it haul wood really well, now it hauls ass!  lol The grippy belt with full sheave stroke is a night and day difference.  The shift out is slow and mild, but the motor pulls down much better - no more crazy RPM to gain a cruising speed.  


So for anyone with a CVTech Powerbloc 50/80 (aka series 0400/0600), CVT and you need to gain about ~10MPH net speed increase,  worn belt or not  just remove that limiter ring. (The REAL benefit of this: will help give the belt more usable life with full sheave stroke, and mellow out the engine RPM) while cleaning the primary pulley assembly --  if you have one of the ASW/Landmaster, BullDog, Land Pride Trekker, etc. utility rigs (not sure what all this clutch setup comes on).  I imagine it was up to the manufacture to install some type of limiter or not as the manual says (1 or 0) so it's not needed for proper clutch operation. I don't know why they cripple a fairly decent clutch like that, I imagine for some 'saaaafety' regulation,  but it really makes the drive setup very inefficient.  Once the weather gets a bit more decent we plan to shoot some video of it running. for the amusement of the five other people that own one of these :)   Has come a long way since dragging it home!    Anyway I hope someone finds this tip helpful, especially if you are going through a lot of belts.   I attached a diagram showing the limiter and a couple pics of the process.  


WP_20190302_11_14_26_Pro (2).jpg


WP_20190302_12_04_04_Pro (3).jpg



  • Like 1
  • Thanks 1
Link to comment
Share on other sites

-----First my required disclaimer:  Don't try this at home!!  -----


Now with that out of the way: Here is a 'drivability profile diagram'  (Reference: Olav Aaen''s vey informative Clutch Tuning Handbook for the scoop on the math behind all this - or this link: https://web.wpi.edu/Pubs/E-project/Available/E-project-022014-185837/unrestricted/MQP_Timothy_DeGreenia_Edited_Jan19.pdf  )

Just to give an idea of the empirical 'shift out' with the CVTech in 7:1 mode,  just subtract 10MPH from the numbers shown in this graph.  (this graph shows the gear ratio 10.15:1 we are using which adds 10MPH to all ratio points in the graph over stock gears)  as stock may be 13.25:1 final drive in these buggies.  Stock top speed for most these UTV's is 25MPH at 3800RPM - = .75:1 final CVT ratio with 13.25 final.  Full stroke allows it to pull to .45 (give or take a couple points due to belt slippage, heat, etc.) at the shift out RPM.  Now this could potentially stall/bog stock engines, (we have not seen this at all) but with a 650cc or larger, should be fine. Not like the clutch is being re-calibrated - just allowed more 'shift out' which holds the engagement or governed RPM more consistent with more pull on top.  Of course I don't suggest driving one of these buggies at 50+MPH,  (or try!) the idea is full use of the CVT ratios.  Much like going from a 4 speed manual, to a six speed manual with some more gears for lugging the engine along.  



  • Like 1
Link to comment
Share on other sites

  • 1 month later...

Thanks Vaughn.  No surprise, but I had never even heard of them until I stumbled upon this one on a facebook marketplace ad, if it weren't so cheap I probably would have passed on it.  Glad I did, we have a blast with it, (the wife and family have a ball in it) it is a lot of fun out on the trails, climbs anything we point it at, hauls a half ton with no issue and cruises on the road 45MPH @ 4000rpm  - and as simple as a lawn mower to work on.  For all around utility, this one is a hit for us.  We have tried to blow it up a few times, but nothing has fazed it yet!

Link to comment
Share on other sites

  • 2 months later...

It's doing great, far better than I expected even. I haven't really done anything to it for the past three months, except drive it. I was worried we would break the Predator engine, but it takes everything we can throw at it. The engine I replaced was a Robin/Subaru EH63. I am running the same CVTech powerbloc clutch, just with a slightly lighter spring , I believe it is the 400/700 spring. Had to go with a lighter spring as the extra torque of the 670 engine over revved (was annoying) a bit at wide open throttle, the lighter spring holds it around 4000-4500, vs 5000-5500 with the original spring. I put new plugs in it around 40 hours ago, and just change the oil. It runs really well now that the jetting is dialed in.  I had to install a wide band O2 sensor to fine tune the Mikuni, but it's about as perfect as I can get it, running around 14.5:1 at cruise, and around 13.2:1 at full power.  I have not put any other money into it, aside from a set of LED lights. The Kevlar drive belt has held up extremely well, even after attempting to smoke it by climbing some very steep terrain fully loaded on a 100+ degree day. If it has a weak link, I haven't found it yet lol

Link to comment
Share on other sites

Just to note, we noticed an oil leak on the 670 on the flywheel side, the frame would get wet with oil.  Upon inspection it was just the oil vapor breather tube came loose and was weeping oil.  I thought maybe it blew a seal out since we run it around 4000-4500 rpm most of the time.  That's the only issue I have had with the new engine.

Link to comment
Share on other sites

Here is a pic of the custom header I made myself, by modifying the golf cart header, just shorted it up, welded it all back up and using the same cheapy muffler, still loud as heck though. Debating a bigger quiet muffler.  Quite a challenge basically doubling the power output in these buggies and the tuning needed to make it work, about the same as any other rig. If I had more time for it, I would put larger disc brakes and a power steering rack in it, with better shocks.  But it does what we need it to, a little too fast at times, if the trails are a bit bumpy.  Not as smooth as the Gator we goof around race with, but it has no problem passing an 800D on the straight and leaving them in our dust :)  Always a riot in our pasture on burn nights lol  





  • Like 1
Link to comment
Share on other sites

  • 5 months later...
  • 3 months later...
  • 4 months later...

I found this thread searching for predator 670 carb tuning tips. Can't believe it didn't come up a long time ago when I was searching for CVTech CVT adjustment info.

I have an American Sportworks Bulldog 300. It's the "300cc" (277cc) version of the same buggy you have, and I also swapped a predator 670 into it. My primary CVT pulley did not have the stoke limiter inside like yours. On mine, the stroke limit was a "feature" of the shaft. I'm curious what year model your buggy is, and why our clutches are different. For my year model I believe the clutches were the same on all the models up to the 650.

In order to free up the primary to spool all the way, I had to put the primary pulley in my lathe and "delete" the stroke limiting "feature." That made a YUGE difference. So I applied the same type of modification to the secondary pulley, allowing it to open up further. Another quite appreciable difference. 

Here are a couple of links with pictures of my modifications to the primary pulley...



...and I'll attach some pictures of my modifications to the secondary pulley.

If you have a friend with a lathe you could probably still apply these concepts to your CVT and get even more shift range and speed out of it. I'm getting 41mph on virtually the same buggy as you, same drivetrain, and with my 670 bone stock. On top of that, something is wrong with my carb and I don't get the 4000 rpm as advertised, never have; I get 3800rpm in neutral, wide open Throttle (measured by handheld tach). I'm guessing no more than 3600RPM at max speed. Once I put a better carb on it and get up to 5000 rpm, I should (by the numbers) be able to hit close to 60mph. But i don't have the cojones for that; this thing feels life threatening already any faster than 35mph. I will make some modifications to the suspension and add some disk brakes front and rear, then maybe we can see about 60mph.

How is that mikuni carb treating you? I'm about ready to send this stock china carb off to that fellow in iceland with all the hydraulic presses.



Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Similar Topics

    • By mcraigchr
      I realize that many of you do not have diesel machines.  For those that do, this is for you:
      Just wanted to post my experience this past week.  Here in Texas, we had pretty good dip in temps.  For 4 days it did not get above 25.  At night, it was single digits or close to it.  I always put Sta-Bil fuel stabilizer in the storage tank (30 gallon).  And up until this tank I was using Power Service (white bottle) for anti-gel.  Never had an issue.
      This tank, however, I switched to Stabil All season (anti gel).  It is supposed to good down to -40.  Zap.  That is a big fat lie.  I put in twice the amount called for in the instructions.  Result was less than optimal.  I drove the SxS 100 feet (to go get the mail) and it died.  I looked at the fuel bowl and it was a cloudy, wax substance.  So, the Stabil did not work.  That said, I'm not sure that I ever tested the Power Service in the same manner.  So I am not saying that one is better than the other.
      What are your experiences?  Are these products inferior?  What do you folks in the northern states / Canada use?  Am I missing something?
    • By Scott Jackson
      What is the Bennche a off brand of?
    • By Cameron
      I did a compression test and was only getting 30 psi. I found that my piston head has insufficient lubrication and/or overheating. I posted pictures to get any thoughts on replacing bore or just have it hone. I know my piston head definitely needs replaced.

    • By tangojay
      Wife and I took a guided tour while visiting Zion Natural Park and well,,,,, the bug hit us HARD. 
      We live in the White Mountains of Arizona, the is many street ATV’s and many trails within driving distance , thus a trailer is not needed for most.
      ‘Here is what we have in our “want” list, 4 seater, doors, street legal , front and rear windshield,,,,, we have not settled on brand or model, so here is we I hope you folks can help us.
      1) Should we buy new or used?
      2) What APR should we expect ( we both have over 800 scores) if we finance?
      3) If we buy used, what should we look for and how many miles is a no go? 
      4) I know it is subjective but, which brand is consider “premium” and which would be considered “entry” 
      Thanks for info you may provide ,
    • By Chris M
      I can shift into reverse and 'high' gear beautifully, but I can't get the UTV to go into low. I hired a mechanic to change the belt, and clean the clutches. When it came back 'low' gear no longer worked.
      I tried to change I've tried replacing fan gears  https://www.amazon.com/gp/product/B08V97JZL5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 that were worn down, and it shifts better but, didn't fix the low gear problem. I can't shift into low with the engine off either. It indicates that it's in low gear, but I hear what sounds like something spinning in the middle of the UTV. 

      It seems like the mechanic didn't know what he was doing. Never even mentioned it to me that 'Low' didn't work, until I went to use the 
  • Create New...