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Old 11-12-2019, 01:59 PM
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Default Predator 670 questions

I've got a few questions about the 670s, one of which I'm planning on using in a future build.

Question 1:
Are the bearing-less engine cranks and journals able to handle short periods of sideways thrust, like a car experiences when using the clutch, or will that wreck the crank and block?

Question 2:
How much power can the original carburetor support? I'm looking for around 30 horses.

Question 2 1/2:
If the stock carb can't support 30hp easily, how do I sync two slide carbs? I think I could make something that would work for an adjustment.

Question 3:
Should I go cheap and get the plain billet rods ($149.50 with no rod bearings) or spend the extra $50 and get a set with rod bearings?

Question 4:
If I'm running an external automotive cooling fan off a flywheel pto, do I need the engine cover, or would it get in the way (I'm looking for the cleanest possible look)? This engine will be in the front of the vehicle.
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Old 11-12-2019, 03:55 PM
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Dude, whatcha tryna build eh?

I'm gonna watch and see if anyone chimes in with prior experience in tinkering with a 670...

But...my experience in general...

#1: I don't think these things are built with thrust bearings like a car, so if you wanna run a manual clutch like runs on a car you need to come up with some kind of torque block/thrust plate between the engine and clutch connection to absorb the thrust...bolt in a plate with a pilot bearing in it or something like that... shouldn't be too hard... think outside the box!

#2: Carbs support air and fuel flow, don't think of it as power. Will it flow enough air to support the proper fuel mix to power a 30hp mill? Can you remove the factory airbox and upjet the carb? In most cases you can. I don't think you will have any problem making 30+go with it if you set it up right.

#2.5: 2carbs? Do you enjoy giving yourself headaches?

#3: you know what you're willing to spend and what your budget is. Personally, I like the idea of being able to replace a rod bearing versus the entire rod should the need arise. Will it make it run any different? Who knows.

#4: I wouldn't put an auto fan on it. I wouldn't pull the cylinder shrouds off either...not to mention the power an auto fan will Rob and those things aren't designed specific for use on an air cooled engine either or higher RPM...
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Old 11-12-2019, 04:46 PM
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Yeah, I was pretty sure that I'd need something. I might be able to use one of the thrust bearings from work. Over the years a handful of the dressers have either broken to an un reparable state or have been dropped, and they have 1" id thrust bearings ion the lower shaft, so I may grab one out of the junk pile. And yes, I do like giving myself headaches. If I didn't I wouldn't be rebuilding my little briggs (it's not the engine i'm using). Ok, I won't run a crank driven fan. Though I may look into an electric fan for it.

And I'm not saying what I'm building yet. I will say to keep an eye out in the next year or two for the build. And it should, by the all knowing and powerful app.kartcalc.net (), be capable of cruising at 60mph (58.8 actually) while turning 3600 rpm. And that's what I'm hoping to get.

And PS, I don't mean clothes dressers, I mean the ones that dress the grinding wheel on a tap machine.
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Old 11-12-2019, 05:48 PM
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Well you could make a belt clutch and tensioner similar to the Pow'r Pup from the 1950s if you are using an automotive transmission. Trying to synchronize 2 carburetors is a huge pain. If you are trying to keep the engine cooler, get a larger oil cooler, but keep an eye on the oil temp, too cold and you could run into problems. I'd spend the money on the rods with bearings.
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Old 11-12-2019, 07:32 PM
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I don't know, I'm kind of afraid of loosing the clutch belt and being stuck somewhere. Plus, I think an automotive clutch could handle the power better. Remember this thing will cruise at 60mph, not the 10-20 that a tractor runs at. And I'd like to keep the engine lower in the engine bay, and the transmission higher above the ground to keep some ground clearance. And now that I think about it, two carbs are a bad idea, so you guys are right about that.
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Old 11-12-2019, 07:58 PM
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I'd be willing to bet the OEM carb is more than capable of doing what you want. I would at least try it first...I have an idea for your clutch mechanism...you need a slip joint to link your power take off to your clutch assy...just that simple...
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Old 11-13-2019, 06:54 AM
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I was thinking that I'd use a slip joint, like you said, with a thrust bearing behind it. And machine a block that attaches to the side cover mounts, to space the bearing out from the engine. And I just remembered the one thing that I spaced on the front part of the dravetrain... the bellhousing. I'm not sure if they make one that factors in the extra length of the adapter. So are they necessary, because I think I might be able to build something that would work.
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