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12-04-2022, 05:37 PM | #1 |
Not Yet Wild
Join Date: Aug 2022
Posts: 51
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JN3 rebuild or ???
So just pulled cart #2 into the garage for the winter project. it is a G14 (I think) with a JN3 - 301 engine. It smokes, but has decent compression. I was planning to just stock rebuild it, as this is the one I am going to eventually sell to pay for the work on my primary limo cart.
While I haven't popped anything open (yet) to see if it's been bored before, looking for experiences with this rebuild - how far is enough to get a decent build ? (yes I know it matters what measurements come out as, if its been bored and so forth) Sort of looking for the most basic rebuild list that I can start to price out. Thanks in advance. Oh, and the ???? part is - I have a 13hp predator, but am hesitant to get into fabrication. I can do it, I just, really don't want to, although if that might be a better way.............. And yes, it's a splash lube, has already been used/beat on a bit former mud motor predator. |
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12-04-2022, 05:45 PM | #2 |
Nincompoop village idiot
Join Date: Apr 2018
Location: Michigan
Posts: 9,625
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Re: JN3 rebuild or ???
If you already have the predator engine, vegas carts has everything you need for an easy bolt in solution to mount it in the cart. Probably run you ~$500-600 for cradle, clutch, belt, and misc parts.
As for the rebuild, nobody can tell you what it needs to be rebuilt. The only thing you can do is grab the service manual, tear it down, and replace anything that’s worn. Plus gaskets and seals and stuff. |
12-04-2022, 05:58 PM | #3 |
Gone Wild
Join Date: Apr 2008
Posts: 2,223
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Re: JN3 rebuild or ???
I have a g2 that has the same engine from g2 to g11 I believe... I have a few rebuild kits in my watch list. here is one for the g14.. they have a version with valves for $120.
https://www.ebay.com/itm/40397610037...id=14052347698 it comes in different bores as well. Theres actually a full rebuild video on ebay. I cant remember if its a g11 or g14 motor though. If its got good compression but smoking its likely just the valve seals which are cheap and easy and prone to smoke on these engines. |
12-04-2022, 06:27 PM | #4 |
Nincompoop village idiot
Join Date: Apr 2018
Location: Michigan
Posts: 9,625
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Re: JN3 rebuild or ???
Actually there’s only a valve seal on the intake valve. And they seldom are an issue.
These engines generally smoke for one of two reasons… either coked up oil control rings stuck in the piston, or the cylinder is shaped like a bell and gets bigger at the bottom. Neither results in a compression loss but can make it smoke like a train. 99% of the time it’s stuck oil rings And for what it’s worth, stick with oem parts. These Yamaha engines do not like aftermarket rings, rod bearings, etc. oem is still available. If you use the aftermarket stuff youre lucky if it makes it a year before it starts smoking again. Cylinder bore is important too. Too rough with the hone grit and it will eat the chrome off the new rings even faster. |
12-04-2022, 07:19 PM | #5 |
VC 460 CLONE GONE WILD
Join Date: Oct 2014
Location: Ray BY The Bay NJ
Posts: 10,593
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Re: JN3 rebuild or ???
I ran my stock G 14 from 2008 to 2014. I bought a smoker for low $'s. The key is don't buy anything until you measure,measure,measure. You don't know where you are until the engine is torn down and you see where the bore is and what it looks like. The only fatal situation is when it is at the max piston size and the cylinder is scored deeply or badly out of round. I agree with use genuine yamaha parts. I was able to get by with being slightly out of stock bore size with new rings and a set of rod bearings. Ran 350 hours and then parted the engine out for $950 and switched to VC 460 power.
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12-05-2022, 12:32 AM | #6 | |
Searching for The Way
Join Date: Oct 2009
Location: Medina, Ohio (NEOHIO)
Posts: 11,421
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Re: JN3 rebuild or ???
Quote:
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12-05-2022, 07:21 AM | #7 |
Gone Wild
Join Date: Apr 2008
Posts: 2,223
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Re: JN3 rebuild or ???
heres a video on a JN6rebuild https://www.youtube.com/watch?v=ZeF-pC4jQJk Id spring for an actual cleaner work bench myself if I were attempting this. This is the first ive heard aftermarket amazon/ ebay kits being bad actually but ill admit I only did a quick google search and read reviews on amazon. I have no actual experience with this kit as some here do.
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12-06-2022, 06:58 PM | #8 |
Not Yet Wild
Join Date: Aug 2022
Posts: 51
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Re: JN3 rebuild or ???
Thanks ! affirmed a lot, it's going to be teardown and get measurements. Bad part for me is finding out if my machinist is still;
a. alive b. working c. wants to hit this small engine While I have the t-handle bore/caliper measuring tools, obviously using the 'right' tool, as well as ability to get good measurements off crank/cam/bearings is better than what I can do. Will update later in the winter on the project/ |
12-06-2022, 07:39 PM | #9 |
VC 460 CLONE GONE WILD
Join Date: Oct 2014
Location: Ray BY The Bay NJ
Posts: 10,593
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Re: JN3 rebuild or ???
With some luck you may not need a machinist. Just the right parts
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12-14-2022, 04:59 PM | #10 |
Not Yet Wild
Join Date: Aug 2020
Location: Maryland
Posts: 8
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Re: JN3 rebuild or ???
Did my G14 a year and a half ago and knew nothing.....was my first cart. (turned out great) i grew up with dirt bikes though so i did have an idea what could come at me. All the Yamaha parts are super available for these and cheap. as said in other posts, make sure u know ur bore size. couple beers and some YouTube time and you're golden!
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