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Unread 01-25-2019, 10:51 AM   #1
Not Yet Wild
 
Join Date: Oct 2016
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Default 81 Marathon 2PG engine rebuild

Recently finished my 2PG engine rebuild out of my 81 EZGO Marathon.
I bought the cart about 2 years ago to cruise around my neighborhood and it's always been loud... I thought the belt clutch might be rattling or maybe the muffler had a loose baffle. It kept getting louder until one day it got much louder and on the way home the engine seized.

I parked it for a bit and lamented my bad luck and finally decided to tackle the problem over x-mas break.

Pulled the engine and I have to say rebuilding the engine was a very fun project (except cleaning 37 years worth of grime off the engine!)

When I pulled the cylinder I found lots of glitter in the engine, one of the crank bearings roller cage had broken and was machining the side of the engine case. Luckily it did no meaningful damage to any important surfaces.


The crank bearings were all gravely and had no evidence of oil, the wrist pin and conrod bearing where covered in thick oil... I wonder if the seals were wore and letting the main bearings get outside air instead of oil mix??? I ran 128:1 oil mix as printed on the gas tank.

I bought a complete crank, rod, piston and cylinder off ebay:

https://www.ebay.com/itm/EZGO-2-Cycl...53.m1438.l2649

the parts went together well and I'm pretty pleased with the quality. The head gasket did get mangled in shipping but I sent the seller an email and they sent a new head gasket out immediately and I received it in 3 days.

I read the flywheel can be a bear to get off but mine pulled right off with my cheap gear puller. Assembly was pretty straightforward, I didn't have a ring compressor but just pushed the rings in with my fingernails and the cylinder slipped right on.

Cart runs great now and is so quiet!

I have to admit that the cart is down a bit on power after the rebuild... It runs great, just not as quick to accelerate... I'd say it runs like I remember them running on golf courses back when I used to golf, before the rebuild it seemed to accelerate faster than the old golf course carts...
I am running 40:1 break in oil and I wonder if that explains the decrease in performance. I checked and rechecked putting the piston port in the proper direction. Also, the timing may have been advanced, I set it per the manual after rebuild.

The governor was removed sometime in its past and the cart would quickly accelerate to 20mph+ before the rebuild which plenty scary in a almost 40 year cart steering/suspension, after the rebuild it tops out at 16mph on a slight climb (very slight) and down the same "hill" it will run 20 or so...
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Unread 01-25-2019, 10:52 AM   #2
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Join Date: Oct 2016
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Default Re: 81 Marathon 2PG engine rebuild

few more pics:
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Unread 01-25-2019, 04:18 PM   #3
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Default Re: 81 Marathon 2PG engine rebuild

I am going to take a guess that the timing is retarded a little. Do you have a timing light ? Should be around 18 degrees BTDC.
Have you checked the compression since rebuild ? It should respond well when you give it the gas. Good job on the rebuild.
Cartaround that is a member here knows much more than I do on the 2 strokes Maybe he can shed some light on your issue.
You were lucky on removing the flywheel. I have almost wanted to hit them with a large hammer :) good job
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Unread 01-26-2019, 08:55 AM   #4
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Default Re: 81 Marathon 2PG engine rebuild

Does it feel faster in reverse? That would be a good indication that your timing is off. It will always be a trade off since the motor runs the opposite direction for reverse, but obviously youíre going to want better performance going forward
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Unread 01-26-2019, 12:57 PM   #5
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Default Re: 81 Marathon 2PG engine rebuild

Nice job.....
I also did this same rebuild on my 85 a couple years ago due to bad crank bearings, And yes the first thing I noticed was it is much quieter. I believe it's from tight crank bearings vs loose.....

Mine still ran fine before the rebuild and had 120lbs compression, But decided to spend the little bit of extra money and do a complete rebuild anyway rather than just the bottom end.

I was a bit disappointed with the compression of the all new top end at only 115lbs, I really expected more then the 32 year old top end had. Still not sure why as I miked-miced-mic'd (used a micrometer lol) on everything and it all was within factory tolerances, But I will say there is no loss in power. In fact I think it runs a bit better.

I agree with above posts, perhaps the timing is a bit retarded. Seems like I put mine just a hair advanced from center, And I mean just a hair...

Also do a compression test, I'm curious to see what you got.

Here's the link to my rebuild, And of course with me I had more complications with the case then you did. But it's all good now.

85 Marathon 244cc Engine Rebuild
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Unread 01-27-2019, 04:05 PM   #6
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Default Re: 81 Marathon 2PG engine rebuild

I too must commend you on your rebuild job. Looks great. As for timing, I would have to agree with trig123. While you mentioned you set it as per the manual, it doesn't take much to make a world of difference in timing. A few degrees of advance could make the difference in how well the cart takes off.

I know it's a PITA to get back behind the flywheel, but if you feel you want more power, you may want to try to advance the timing plate a little to see if that help

To advance the timing, rotate the timing plate clockwise.


Dabble Inn also has a good point. A compression test wouldn't hurt, but if you didn't do one before the rebuild, you don't really have a baseline to compare your readings. Since you have a manual, you can see what you have compared to what the manual says.


Good Luck!!!!!!!
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Unread 02-03-2019, 01:22 PM   #7
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Default Re: 81 Marathon 2PG engine rebuild

Thanks for the kind words. The cart is slowly getting more power as I drive it more and more, hard to get time on the engine in a Colorado winter.

I checked compression today, engine hot, wot 100 psi

Haven’t checked timing, but I have to say it runs just fine and without the governor hooked up I’m okay with the slightly low power output, especially when I loan it to my friends.
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Unread 02-04-2019, 05:13 PM   #8
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Default Re: 81 Marathon 2PG engine rebuild

Quote:
Originally Posted by flashboiler View Post

Havenít checked timing, but I have to say it runs just fine and without the governor hooked up Iím okay with the slightly low power output, especially when I loan it to my friends.
I assume you meant to say WITH governor hooked up not without.... I guess it's ok to have it hooked up for your friends but it'll run a lot better without it for you, I bought mine about 20 years ago and owned it for all of 15 minutes before removing it. And all the parts went directly into the trash lol...

100 lbs compression is a little disappointing just like mine was but it is enough
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