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Mac, your name came up on a 300 page on FB.

So I now have 3 4wd 300's in the yard. I don't buy beaters unless I plan on going through the motor and making sure they're cleaned out and good to go, so all three I will split cases and clean out the bottom end.

I understand that one can put a 350 Foreman top end on these with some extensive work, but if I'm splitting cases anyway....

I have a 350D in the yard where I can get the top end bits.

I know I will need the 350D crank machined (found a source for that, about $275)

I know I need a "reverse grind cam" and not sure where to get that or cost.

I have a jug, head, rocker box etc. What else do I need, and more importantly, is it worth it?

To get into the gearhead discussion again, why is this better than the 317 bolt on cylinder and piston? I'm guessing the 350D crank adds some oomph, but what do I know.....
 

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Phew, thought I was in trouble again LOL

So if you've got the parts on hand to do it, it's really not that involved....

Crank machining isn't that bad, I had mine done locally I don't think it was anywhere near $275 USD, I did have a bunch of other stuff being worked on at the same time and paid cash for it all though. You do want it done RIGHT, I mean if that taper is off the the flywheel doesn't run dead nuts true your going to chew up crank bearings. So if you can take it to somebody you trust will do it right it's worth paying extra.

Reverse grind cam comes from Megacycle, Web may do them but not sure. I got mine from FST but I'd steer clear of that outfit. The rerverse grind cam basically has the lobes flipped 180° from a standard cam IIRC. You obviously have this figured out but for anybody else, the 350D engine runs in the opposite direction compared to the 300 motor.

You need the crank, jug, head, rocker box...basically the entire top end. You can run a stock piston, or whatever you like. Beyond +2mm or so you'd need a new big bore sleeve and I don't know if the 300 crankcase would have the clearance for that. So if you do decide you want to do something like the XR500 BBK in it (89-93mm? bore) you'd want to have the cases bored out to match the sleeve before you put it back together. You'll also need to move the timing chain tensioner to the opposite side of the jug, not a big deal as the mount for it is already there on the 300 cases. Outside the motor you'll need a full custom exhaust, the 350D exhaust can be made to work but heads out the opposite side of the machine as the factory 300 exhaust did. You can use a 350X or 400EX head pipe to have it go out the same side as stock but no matter what expect some cutting and welding. You'll also need to fabricate a new top motor mount. Despite what many say you do not need to have a frame lift in the machine for the motor to fit.

I don't know if it's better than a 317, I mean it's all in the way you look at it. The 317 is a great bang for your buck kit, uses all OEM parts, makes decent power etc. But you're still limited by that 2 valve head. Going to 350cc 4 valve head is just next level, but it is more work. The 300 should make about the same power as a stock 350D with this 350D top end on it, the only things that will change it are your exhaust, and whatever carb your running. Without knowing exactly how much torque the 300 makes I can't say exactly how much difference the 350cc upgrade makes, but power wise you're looking at about a 8hp boost (16 to 24), which is pretty significant.
 

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Discussion Starter #4
Phew, thought I was in trouble again LOL

So if you've got the parts on hand to do it, it's really not that involved....

Crank machining isn't that bad, I had mine done locally I don't think it was anywhere near $275 USD, I did have a bunch of other stuff being worked on at the same time and paid cash for it all though. You do want it done RIGHT, I mean if that taper is off the the flywheel doesn't run dead nuts true your going to chew up crank bearings. So if you can take it to somebody you trust will do it right it's worth paying extra.

Reverse grind cam comes from Megacycle, Web may do them but not sure. I got mine from FST but I'd steer clear of that outfit. The rerverse grind cam basically has the lobes flipped 180° from a standard cam IIRC. You obviously have this figured out but for anybody else, the 350D engine runs in the opposite direction compared to the 300 motor.

You need the crank, jug, head, rocker box...basically the entire top end. You can run a stock piston, or whatever you like. Beyond +2mm or so you'd need a new big bore sleeve and I don't know if the 300 crankcase would have the clearance for that. So if you do decide you want to do something like the XR500 BBK in it (89-93mm? bore) you'd want to have the cases bored out to match the sleeve before you put it back together. You'll also need to move the timing chain tensioner to the opposite side of the jug, not a big deal as the mount for it is already there on the 300 cases. Outside the motor you'll need a full custom exhaust, the 350D exhaust can be made to work but heads out the opposite side of the machine as the factory 300 exhaust did. You can use a 350X or 400EX head pipe to have it go out the same side as stock but no matter what expect some cutting and welding. You'll also need to fabricate a new top motor mount. Despite what many say you do not need to have a frame lift in the machine for the motor to fit.

I don't know if it's better than a 317, I mean it's all in the way you look at it. The 317 is a great bang for your buck kit, uses all OEM parts, makes decent power etc. But you're still limited by that 2 valve head. Going to 350cc 4 valve head is just next level, but it is more work. The 300 should make about the same power as a stock 350D with this 350D top end on it, the only things that will change it are your exhaust, and whatever carb your running. Without knowing exactly how much torque the 300 makes I can't say exactly how much difference the 350cc upgrade makes, but power wise you're looking at about a 8hp boost (16 to 24), which is pretty significant.
Chris Clark is the one doing the crank machining. It's $250 including shipping.

I dunno. Figure that in with the cam, then custom exhaust, then I'm guessing I'd need a new carb too, and suddenly I'm at $$$$.

What did the cam run you, ballpark? Neither place you listed has much of a website, but then again for custom work that's to be expected.
 

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wouldnt a 350 carb be upto the job? A few jets maybe?
 

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Yeah for the custom stuff you'd have to contact them anyway. I feel like it was like $250-300 but it was 5 years ago or more. lol

350D Carb should work fine as long as it fits in the boot on the airbox side. 300EX carb would also work.

It's expensive for sure. Doing this much work you'd be just as well off to go the big bore route. Mine with the 90mm piston came out to 432cc, probably makes 35-40hp or more. 317 would never touch it.
 

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Another option is the 380 kit. Mr crankshaft will put a big red rod on your crank for 199. Then get your jug bored to fit a foreman 400 sleeve/piston. Factory Honda parts with 4 factory over bores. That is what I will be doing.
 

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Your still limited with the stock 2 valve head though. At 380cc your +100cc over stock trying to get all that extra air through the same head and intake. Bigger valves and a port and polish would make a huge difference on a motor like that.
 

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Your still limited with the stock 2 valve head though. At 380cc your +100cc over stock trying to get all that extra air through the same head and intake. Bigger valves and a port and polish would make a huge difference on a motor like that.


It's been done with no noticeable difference. I will be using the stock head with 459 cam on my build
 

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mac 350D Carb should work fine as long as it fits in the boot on the airbox side. .[/quote said:
I don't know if the 350D fits , the later model 350's do
An excuse for a nice custom alloy airbox then ;-) lol
 
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