4stroke marathon engine problems

caddymankc · 02-02-2008, 06:17 PM

I found out today im getting a 4stroke marathon, but it has engine problems.Does anybody know why it would back fire and shoot flames through the carb?Im trying to see what i all need to check.

CC-John · 02-02-2008, 07:03 PM

If it's a 295 Robin, maybe the timing belt has jumped a tooth???

caddymankc · 02-02-2008, 07:41 PM

It would be a 295 how hard is it to set the timing back? I was thinking something with the valvetrain to but how would it jump like that?

CC-John · 02-02-2008, 09:09 PM

Quote:

Originally Posted by caddymankc

It would be a 295 how hard is it to set the timing back? I was thinking something with the valvetrain to but how would it jump like that?

The timing belt tensioner has probably never been adjusted.. The 295/350 Robins have a spring loaded tensioner pulley.. The pulley bolt has to be loosened, then rotate the engine one rotation by hand to allow the tensioner to tighten the timing belt, then retorque the retaining bolt.. There is a rubber plug in the timing belt cover that allows access to the tensioner bolt.. The tensioner should be readjusted every 500 hours..

Here's a link to the service manual, it has the diagram you'll need to retime the engine..

Robin 295/350cc Service/Parts Manual

Hope this helps...

scottyb · 02-02-2008, 09:14 PM

Sounds like you made out like a bandit, caddyman. Let us know what it looks like when you get it!

ruredy · 02-02-2008, 09:40 PM

I really, really, really don't think it's jumped time, it's either bad valves or they need adjusted. They never do that without destroying the belt, so unless it was put back together wrong thats not the problem. Of course I may be wrong and your engine could be the only one that has.

caddymankc · 02-03-2008, 06:53 PM

I found a diagram and it showed the cam running on gears off the crank and a belt off the crank, or am i looking at the diagram wrong?

caddymankc · 02-03-2008, 06:53 PM

caddymankc · 02-03-2008, 07:15 PM

How much would it cost to rebuild the head?Im pretty sure the pistons and rings are gonna be fine, but i figured it was gonna be something in the topend.I dont got the cash to bigblock it so thats out of the question.lol

CC-John · 02-03-2008, 07:36 PM

The camshaft is located in the cylinder head, it is driven by the belt from the balancer shaft located in the block.. The balancer shaft is driven by the crank thru a set of gears..

I concur with ruredy, check the valve lash.. If the valves haven't been adjusted in years, the lash may be so tight on the intake valves they're not closing all the way.. Either way, I would do a good tune-up (plugs, air filter), adjust the timing belt tensioner, and check the valve lash as a good first start..

02-02-2008, 06:17 PM	#1
caddymankc WILD Join Date: May 2007 Location: lebanon county,pa Posts: 1,266	4stroke marathon engine problems I found out today im getting a 4stroke marathon, but it has engine problems.Does anybody know why it would back fire and shoot flames through the carb?Im trying to see what i all need to check.

02-02-2008, 07:03 PM	#2
CC-John prop. A$$hole's Garage Join Date: Dec 2007 Location: Deep inside the Central Scrutinizer (77096) Posts: 1,587	Re: 4stroke marathon engine problems If it's a 295 Robin, maybe the timing belt has jumped a tooth???

02-02-2008, 07:41 PM	#3
caddymankc WILD Join Date: May 2007 Location: lebanon county,pa Posts: 1,266	Re: 4stroke marathon engine problems It would be a 295 how hard is it to set the timing back? I was thinking something with the valvetrain to but how would it jump like that?

02-02-2008, 09:14 PM	#5
scottyb Happy Carting Join Date: Dec 2007 Location: Southern California Posts: 73,408	Re: 4stroke marathon engine problems Sounds like you made out like a bandit, caddyman. Let us know what it looks like when you get it!

02-02-2008, 09:40 PM	#6
ruredy Born Wild Join Date: Mar 2007 Location: Clover SC. Posts: 5,552	Re: 4stroke marathon engine problems I really, really, really don't think it's jumped time, it's either bad valves or they need adjusted. They never do that without destroying the belt, so unless it was put back together wrong thats not the problem. Of course I may be wrong and your engine could be the only one that has.

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02-03-2008, 06:53 PM	#7
caddymankc WILD Join Date: May 2007 Location: lebanon county,pa Posts: 1,266	Re: 4stroke marathon engine problems I found a diagram and it showed the cam running on gears off the crank and a belt off the crank, or am i looking at the diagram wrong?

02-03-2008, 07:15 PM	#9
caddymankc WILD Join Date: May 2007 Location: lebanon county,pa Posts: 1,266	Re: 4stroke marathon engine problems How much would it cost to rebuild the head?Im pretty sure the pistons and rings are gonna be fine, but i figured it was gonna be something in the topend.I dont got the cash to bigblock it so thats out of the question.lol

02-03-2008, 07:36 PM	#10
CC-John prop. A$$hole's Garage Join Date: Dec 2007 Location: Deep inside the Central Scrutinizer (77096) Posts: 1,587	Re: 4stroke marathon engine problems The camshaft is located in the cylinder head, it is driven by the belt from the balancer shaft located in the block.. The balancer shaft is driven by the crank thru a set of gears.. I concur with ruredy, check the valve lash.. If the valves haven't been adjusted in years, the lash may be so tight on the intake valves they're not closing all the way.. Either way, I would do a good tune-up (plugs, air filter), adjust the timing belt tensioner, and check the valve lash as a good first start..

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