Marathon engine issue

Tdfrancis · 04-09-2019, 09:13 PM

Ok I just had my robin 295 sent out for a rebuild. I figured this would be faster for me and less hassle. However now that I got it back I can’t get it to start. New rings valve guides and seals. All new gaskets. So I checked my compression and I’m seeing 50psi on each cylinder 😡 is there any reason why I should be seeing such low psi. The motor had 150 psi before I sent it off and ran fine but was smoking. Any ideas on what may be going on here.

Rooster59 · 04-10-2019, 10:15 AM

A silly long shot but double check that the valve gap is .004".

CP241 · 04-10-2019, 10:27 AM

Make sure when checking compression you are holding the throttle at the carb all the way open with your fingers. Don't rely on the governor to do it. Throttle closed will make a huge difference when doing a compression test. IF the engine isn't sucking enough air in, it obviously won't be able to compress it!

If compression truly is at 50psi, and you're sure your gauge is accurate, then I would get in contact with whoever built your motor. They obviously did something wrong...

Tdfrancis · 04-10-2019, 03:36 PM

Ok so I just realized it is blowing air out the carburetor into the air filter what can cause this.

Tdfrancis · 04-10-2019, 04:16 PM

If the timing was out 180 would that effect the compression and would it blow gas out the carb?

cart around · 04-10-2019, 04:48 PM

Sounds like the intake valve is open. Adjust the valve gap to .004"

Tdfrancis · 04-10-2019, 07:37 PM

Well I got this solved. When I took off the valve cover to inspect and adjust all clearances were perfect. So I started thinking what about the timing. I pulled the plugs and discovered top dead center and started rolling it over by hand. I noticed the exhaust valve was open at top dead center. I pulled the timing belt cover off as best as I could since it’s still in the cart and looked to see what I could see.... not much lol. I put at top dead center and then slipped off the timing belt (sounds so easy) and adjusted the cam so the intake valve was just about to open. Put it all back together and it fired right up! I checked the pressure and I’m reading about 100psi after about 15 seconds of run. So perhaps the rings need to seat or the timing is not quite right yet. I’ll know more once I run it for a bit.

trig123 · 04-10-2019, 07:51 PM

You moved the timing belt and guessed which way it went ????

Tdfrancis · 04-10-2019, 08:11 PM

Quote:

Originally Posted by trig123

You moved the timing belt and guessed which way it went ????

Yes I moved the timing belt. I would not say it was a guess as much knowing how an engine is soposto work. It was obvious to me where the cam should be when the pistons are at top dead center. It would have been nice to see the setup marks but that was not an option.

CP241 · 04-10-2019, 08:14 PM

You need to align the Mark's correctly. They're pretty clear where they need to be. Guessing ain't gonna cut it.

04-09-2019, 09:13 PM	#1
Tdfrancis Not Yet Wild Join Date: Sep 2017 Location: Nova Scotia Canada Posts: 45	Marathon engine issue Ok I just had my robin 295 sent out for a rebuild. I figured this would be faster for me and less hassle. However now that I got it back I can’t get it to start. New rings valve guides and seals. All new gaskets. So I checked my compression and I’m seeing 50psi on each cylinder 😡 is there any reason why I should be seeing such low psi. The motor had 150 psi before I sent it off and ran fine but was smoking. Any ideas on what may be going on here.

04-10-2019, 10:15 AM	#2
Rooster59 Gone Wild Join Date: Jul 2017 Location: East Central Missouri Posts: 1,955	Re: Marathon engine issue A silly long shot but double check that the valve gap is .004".

04-10-2019, 10:27 AM	#3
CP241 Nincompoop village idiot Join Date: Apr 2018 Location: Michigan Posts: 9,683	Re: Marathon engine issue Make sure when checking compression you are holding the throttle at the carb all the way open with your fingers. Don't rely on the governor to do it. Throttle closed will make a huge difference when doing a compression test. IF the engine isn't sucking enough air in, it obviously won't be able to compress it! If compression truly is at 50psi, and you're sure your gauge is accurate, then I would get in contact with whoever built your motor. They obviously did something wrong...

04-10-2019, 03:36 PM	#4
Tdfrancis Not Yet Wild Join Date: Sep 2017 Location: Nova Scotia Canada Posts: 45	Re: Marathon engine issue Ok so I just realized it is blowing air out the carburetor into the air filter what can cause this.

04-10-2019, 04:16 PM	#5
Tdfrancis Not Yet Wild Join Date: Sep 2017 Location: Nova Scotia Canada Posts: 45	Re: Marathon engine issue If the timing was out 180 would that effect the compression and would it blow gas out the carb?

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04-10-2019, 04:48 PM	#6
cart around Test before replacing Join Date: Aug 2013 Location: Ohio side of the Pennsylvania border. Posts: 3,496	Re: Marathon engine issue Sounds like the intake valve is open. Adjust the valve gap to .004"

04-10-2019, 07:37 PM	#7
Tdfrancis Not Yet Wild Join Date: Sep 2017 Location: Nova Scotia Canada Posts: 45	Re: Marathon engine issue Well I got this solved. When I took off the valve cover to inspect and adjust all clearances were perfect. So I started thinking what about the timing. I pulled the plugs and discovered top dead center and started rolling it over by hand. I noticed the exhaust valve was open at top dead center. I pulled the timing belt cover off as best as I could since it’s still in the cart and looked to see what I could see.... not much lol. I put at top dead center and then slipped off the timing belt (sounds so easy) and adjusted the cam so the intake valve was just about to open. Put it all back together and it fired right up! I checked the pressure and I’m reading about 100psi after about 15 seconds of run. So perhaps the rings need to seat or the timing is not quite right yet. I’ll know more once I run it for a bit.

04-10-2019, 07:51 PM	#8
trig123 Vintage tech Join Date: Sep 2009 Location: South Posts: 3,216	Re: Marathon engine issue You moved the timing belt and guessed which way it went ????

04-10-2019, 08:14 PM	#10
CP241 Nincompoop village idiot Join Date: Apr 2018 Location: Michigan Posts: 9,683	Re: Marathon engine issue You need to align the Mark's correctly. They're pretty clear where they need to be. Guessing ain't gonna cut it.

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