Re-engine Buggy with a (modified) Predator 670

[darwinpayne2000]

My single-seater buggy has been kicking around in one form or another for the past 17 years. For most of those years, I've been running a B&S Vanguard engine that I modified with high compression pistons, camshaft, Mikuni carb, etc. It was pretty good in it's day, but the engine is using a fair amount of oil lately and it just doesn't seem to have the same "oomph" that it had a few years ago.

I could refresh the engine and bring it back to it's old self, but I'm loathe to spend more money on it. The biggest problem, for me, is that my engine is the smaller 14-16 hp (400cc) engine block. I've installed all the performance parts and bumped up the horsepower, but that old adage that "there's no replacement for displacement" is still true.

I've looked at the Harbor Freight Predator 670cc engine in the past, but the engine lacked an installed base of users in the off-road sport and there was no source for performance parts. That changed a few months ago when Performance 670 started making/supplying parts for revving up these engines.

So I was kind-of ready to take the plunge after I looked at the Performance 670 website but I was still hesitant. You can certainly get some nice pistons, camshafts, springs etc for the engine, but you can also spend a small fortune chasing a few extra horsepower. There's cheaper ways to do it. On the other hand, my buggy is a true "minibuggy" and fitting a non-industrial engine into the back would be a challenge. Yes, a motorcycle engine would fit, but I'm a CVT kind-of-guy. Working a clutch seems so-o-o 20th century these days.

I was still sitting on the fence until I opened my monthly (daily!!) Harbor Freight email and . . . there it was. A coupon to get $80 off the regular price of the Predator 670 engine. It was a sign. I ran down and picked up the engine before I started having second thoughts.

So, the engine is sitting in my garage right now. I'll post up some pictures shortly and describe what I have in mind. My goal is to install the engine in a (mostly) stock configuration and make some changes over the next few months to see what kind of performance bump I get on each modification. I'm posting this project because there might be some other guys interested in what can be done with a Predator 670 and what it will cost.

[darwinpayne2000]

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So, the old engine is out of the buggy and I have it sitting next to the new Predator 670. At first, it looks like the 670 is much larger, but a closer look shows that the Predator appears bigger due to the air filter on top of the engine. I measured the length and width of the Predator and compared it to the old Vanguard. The engine block is only slightly wider and taller, but the oil cooler and the engine controls on the front and back give it a bigger appearance. Also, if you look at the PTO shaft, it's the same height as the Vanguard. That makes sense if the Predator is designed to be a direct replacement for a Vanguard or Honda engine.

One "big" difference, however is the weight of the engine. I can grab hold of the Vanguard engine and heft it around, but the Predator is just a few pounds too heavy. I managed to leverage it into the back of my pickup and slide it back out, but I can't pick up the engine and carry it around. It's just too heavy to safely move around without a second person to help.

I also took a look at the mounting holes on the bottom of the engine. The engine will fit on the mounting bolts of my old Vanguard, but it's more of a "compatibility mode". It's kind of loose and sloppy because the mounting holes on the Vanguard are 5/16" and the Predator will be much happier with 7/16" bolts (to eliminate the "slop"). To anchor the engine properly, I need to make a new mounting plate for the engine.

[LIDUNO]

The links don't seem to work.

[darwinpayne2000]

The images should now be fixed.

[LIDUNO]

Yup! working good now.

I remember back in the day there were aluminum BS 5 horse motors that all the gokart racers wanted, and then there were iron ones. Is the case on the vanguard aluminum and the case on the Predator iron? I only ask cause you mentioned it was so much heavier.

[neo71665]

They both are aluminum cases but you also have to think it's adding 200 (ish) CCs to it. The case just has to be that much bigger.

[LIDUNO]

Ah ok! I missed that part, makes sense then.

[darwinpayne2000]

So, the first step was to build a new mounting plate for the Predator 670.

Estimated Time for Project: 3 hours

Actual Time: 3 Days

I trotted down to MetalMart, a local steel supplier and picked up a 1/4" remnant steel plate for cheap. It took a few minutes to puzzle out the Predator bolt pattern onto the new plate, but I was making good time, until . . . I laid out the nearly completed mounting plate in the buggy and discovered that the engine needed to sit one inch further forward to keep the oil cooler from hitting the frame. Dang!!

I couldn't just redrill the mounting holes without making a mess of the plate, so I started over. At that point, I kind of lost the momentum and it seemed to take fore-e-e-v-ver to finish that ##$% mounting plate.

Now it's finally done. The mounting plate keeps the engine, primary jackshaft and the driven clutch in alignment. If I need to tighten the chain, I just slide the whole assembly back. Easy peasy. I mounted up all these pieces and parts and dropped it into the frame. The overall fit looks pretty good. The only clearance issue I have is the gas tank. It normally sits fairly close to the right-side of the Vanguard engine, but the Predator is a little too wide to leave it as-is. I need to re-situate it . . . somehow. It will work if I move it up and back, but that would shift more weight to the back, which I would like to avoid.

Now for the sad part. Earlier, I took the muffler off so I could manhandle the engine. After dropping the engine into the frame and putting the muffler back on, I discovered that the exhaust points forward!!! (No, I didn't put the muffler on backwards. It only fits one way.) It threw me for a loop. I had to look at the picture on the box to confirm that Harbor Freight actually designed it that way. So, before I take it out on the trail, I need to either redirect the exhaust or, more likely, replace the exhaust system with a custom setup.

(Maybe Harbor Freight anticipated this issue? The engine ships with two extra sets of exhaust gaskets.)

The next step is to fire up the engine and see how it runs. I still have a few more tasks ahead before it's ready to take out on the trails. I'll provide more details in another post.

[neo71665]

Either swap the end caps on the muffler or just weld up the outlet and drill a new on on the other side. Quick and dirty but if your gonna build something better later it works.

[K-fab]

Can you cut the header tube off at the muffler and spin the muffler around so it points back?