Hawk engine swap to Zongshen PR250/300

[Dusman]

This thread is for those who are interested in installing the counterbalanced, 6 speed Zongshen PR250 or PR300 engine into their carbureted Hawks.

I just installed the Zongshen PR250 6 speed counterbalanced engine in my Hawk this past weekend. It shares the same bottom end/crankcase as the PR300. These engines will fit the Hawk, but certain necessary and significant frame modifications need to be made in order to make it fit inside the Hawk's engine bay and to run the engine with the carbureted Hawk's wiring harness.

A. Some engine mounts have to be cut out and re-welded back in. There's two ways to do this:

1. You either have to cut out the lower front mounts, install the motor into all of the other mounts (except the upper mounts, more on that later...). Then, weld the lower front mounts back onto the frame with the lower front mounts *attached* via the bolts to the PR250 engine while you weld it in place. Then, you'll have to remove the engine again, finish welding the lower front mounts in from the top of where the mounts come into contact with the frame tubes, re-paint that area, then re-install your PR250/300 engine. Also, for the upper front mounts, the ones that require 3 bolts, you'll have to re-make your own mounts with 1/8" thick flat steel (3" width) purchased from the hardware store. See also # 3 below. That's the method I chose.

2. The second way is that you can cut out the rear middle mount tange on the right side that comes off the rear cross member of the frame to get the engine in the bay. Second, you have to elongate the holes on the lower front mounts. Now, your engine will fit in the engine bay, but if you re-weld the rear middle mount's tange back to the frame, I'm not sure you'll be able to easily get the engine out again. With the method I used above (1), you can get the engine in and out as needed, though it takes some work as it's tight in there!

3. This last part isn't necessary, but for me, I did it as I felt like I need the extra wiggle room for the engine. Where the front downtube of the frame comes down and splits into the dual spar frame configuration, where the downtube continues straight and slightly extends beyond the tubes on either side that make up the "spar", I cut that out with angle grinder to allow more room for the counterbalancer at the front of the engine. Two other fellows in the Hawk 250 FB group that installed this engine didn't do that, but apparently it wasn't necessary for them. For me, it significantly helped provide more room for the engine's counterbalancer without sacrificing frame integrity.

B. Now, to get the PR250/300 to run on the carbureted Hawk's wiring harness, you'll have to remove the stator, stator wires, and flywheel from your Hawk's stock CG 250 motor and install them into your PR250/300 engine. While you could theoretically avoid having to do this by completely changing your electrical system over to a GPX FSE 250e or Templar X 250 wiring harness & system, good luck finding one of those since as of the writing of this post, they have been for me, totally unobtanium.

It's a lot of work, but it's worth it for me to have the 6th gear, the counterbalancer, and the ability to ride comfortably at 60-65 mph without having to lose that low tractor-factor with first gear for off-roading.

[Dusman]

To fit in the PR250/300 engine into the engine bay, you have to do the following:

1. You have to round out the end of the down tube that extends beyond the twin spar part of the frame or the front of the engine will not be able to fit due to the counterbalancer. I cut a "V" in there with a cutoff wheel with an angle grinder and then rounded it out with a Dremel tool using a cobalt grinding bit. You can see the area that needs to be removed in the photos below with the circled areas.

[Dusman]

2. Carefully cut out the lower front engine mounts, re-install the engine into the engine bay, then tack weld the lower front engine mounts into place (top photo). This will allow you to finish re-welding them back onto the frame after you remove the engine (bottom photo). You can also see in the top photo how notching out the end of the downtube in step # 1 allows just enough clearance for the counterbalancer.
See photos below.

[Dusman]

3. Fabricate the top front engine mounts. This will be necessary due to the fact that the OEM top front engine mounts are not long enough to reach the recess into the engine where the engine mount bolts mount to these mounts. I re-installed the engine via the rear and top mounts only, used cardboard to get a general idea of the size I needed, cut it to fit and then poked holes into the cardboard exactly where the mounting bolts go through. Then I took a piece of 3/8" stock steel I purchased from the hardware store, cut it to fit with a cutoff wheel on my angle grinder, checked fit, then ground it down the rest of the way with a bench grinder to where it fit perfectly. I then drilled holes through the steel using carbide bits and an electric drill. This step will also give you a chance to check that your lower frame engine mounts still fit after repositioning them and re-welding them back in. Make sure to put the engine mounting bolts through those lower frame mounts to ensure a good fit. See photos below of fabricated front upper engine mounts below.

[Dusman]

4. Reinstall engine for (hopefully!) the last time. Check engine fitment at all mounts via re-installation (front lower, front upper mounts, top mount, top rear, and bottom rear mounts). See photos below.

[warrenpeas]

thank you for making this post. im thinking about the pr300 for a different application. how does the dimensions of the pr250 compare to the cg250?

[Dusman]

Good question. The motor is definitely wider and only slightly taller than the CG250 engine, but will fit in my Hawk’s engine bay with some modifications to the frame mounts as noted below. Here is a great site that provided the PR250/300’s dimensions when you click through the provided drawings to the left of the webpage. I hope this helps!
https://aj1moto.com/collections/engi...n-pr250-engine

[Dusman]

[Shinigami117s]

Is the cg 250 is a dc cdi system?
I have a ZS172FMM-5 engine also but cannot get it to fire with the dc cdi unit that came with it…

[Dusman]

I simply switched out the stator that came with my PR300 engine to my Hawk’s original stator and wiring harness. It fired right up with that set-up!

[Megadan]

Same basic changes that have to be done to install the RE250 6 speed engine. Seems to be a common theme with swapping a newer gen counterbalanced OHC engine into the Hawk frame.

[Dusman]

Several folks have asked me to provide a video about the major modifications that I have made to my Hawk250, including the Zongshen PR300 motor. Here you go!