85 marathon rebuild

[tabaker]

I bought this cart last Sunday. It was cold out, 15 degrees, so I didn't test drive or look at it too much so I was a lil worried about what I was getting. Wednesday and Thursday it warmed up so I drove it around in the yard and was pretty happy with the way it was running at 30 degrees except for that backfire. Usually a little back fire but one yesterday was really loud. I have been reading this forum all week so I thought I would adjust the throttle cable this morning to get rid of that backfire. So I put the missing spring on and thought I had it adjusted perfectly. I noticed the choke was opening all the way and then past so I adjusted that to. While I was at it I put in a new battery. Oh and I plugged the old oil injection line. I pushed down on the pedal with a big smile on my face and listened to it crank and crank and crank. Crap. I thought the gas tank was empty so added gas. Crank crank nothing. Pulled gas line off at carb and pretty crappy flow so I replaced filter. Crank crank crank. Still not much gas flow. Then I notice a puddle of gas under cart. Looked around and found it had a blown cylinder base gasket. double crap. Could that last backfire have got me? Removed engine then cylinder head and also found top ring broke. Crap Crap Crap. So am planning on new piston/rings and gaskets. Also replacing crank seals while I have it out. Do you think I should replace anything else while I have the engine out? Thanks...

[Vavoomskill]

If it's out and apart I'ed do anything that wears out! don't go crazy... if it doesn't need a crank or main roller bearings then obviously save the cash. this is a good time to port the jug though and mill the head a bit for a bit more power. make sure the throttle shaft isn't real loose n sloppy, that can cause the back firing too

Best of luck and fun to ya!

[racin161]

Welcome TA Sure if the base bolts were loose a backfire would do it and believe me these bolts are over looked and should be checked every so often they will loosen with heat cycles. once or twice a season along with exhaust bolts. Now your on the right track with replacing the crank seals at this point. BOTH need to be changed. Before you start grab the drive clutch and see if there is any movement in the crank if not proceed with the top end rebuild and your good to go. Be sure to BLUE LOCTITE your seals when installing and lube the rubber seal lip. Hope this helps.


LOU

[tabaker]

When u check for play in the crank do u just go by feel? Same for connecting rod bearing? Both felt good. I have rebuilt a couple 80hp outboards and a few jet ski's that was all I did for those. Maybe flying by the seat of my pants.
Also if there is a lot of play in the throttle shaft is that fixable or is it just wore out?

Thanks...

[Vavoomskill]

Originally Posted by tabaker

When u check for play in the crank do u just go by feel? Same for connecting rod bearing? Both felt good. I have rebuilt a couple 80hp outboards and a few jet ski's that was all I did for those. Maybe flying by the seat of my pants.
Also if there is a lot of play in the throttle shaft is that fixable or is it just wore out?

Thanks...

It's just wore out... unless you fab up a new one !! and drill - ream the hole to .250 which is a standers size of brass stock you can buy Here's the one I made for mine...
[IMG][/IMG]

[Vavoomskill]

I made this with a hand file a #4 tap and a 1/4 20 die. it took me about an hour. When I was done fitting it I ground the back side of it so it would flow better because it's a tad bigger in Diameter than stock which I think is metric.....
Hopes this helps and inspires you to give it a try and save a buck! and not have a China carb

[tabaker]

Wow great workmanship! I will have to give that a try or maybe you should start mass producing.

I spend most of my money on women and booze. The rest I waste...

[sassycat]

same here,,85 marathon reconstruction..have fun,,just ordered a jakes long travel to convert on my ole blue cart..in my build thread,,have fun playin with the new toy,,these motors last forever and are easy to get runnin,,good luck