1989 Marathon 2PG Engine Rebuild- In over my head - Please help

[TexasHunter]

Hello Guys,

I bought a 1989 Gas Marathon that was running great at the time. I purchased a 4 in lift and bigger tires and was successful with the instal. After running it for about 4 months, I started to notice an occasional backfire in the engine that happened infrequently. Next thing I know, the engine wont start.

I researched through the wealth of knowledge and information here in BGW and decided I would tackle an full engine overhaul even though I am a novice mechanic with very little experience. I figure if it is not working then I don't have much to lose so I would learn by doing and tackle the project.

So far I have been able to:

• Pull the engine
• Remove the drive clutch
• Clean it up thoroughly
• Remove the cylinder

I need to ask for coaching on the next steps to remove the flywheel and be able to crack open the crank case.

Attached are a few pictures of the engine in it's current state:

I noticed when I was doing the tear down that the crank shaft has a small vibration in it and that I can feel air come out of the clutch side seal when I manually spin the crank.

Here are my specific questions:

• What is the proper sequence to remove the components and crack open the crank case?
• How do I remove the flywheel?
• Should I bring the new crank shaft to a machine shop to have the bearings set? Any tips here?
• Do I need to make any marks to act as a guide for reassembly to make sure the timing will be correct?
• Any general tips regarding a lower end rebuild process that I have not asked to correct questions?

I found good videos and guides for rebuilding an upper end but not the lower side. Any tips / coaching or advice would be greatly appreciated. I am enjoying the challenge of this project and sharing the experience with my son and would like to be able to complete the project without having to go to a small engine repair shop if I can help it. Thanks in advance for your replies.

Best Regards,
Stephen

[Dave Box]

Congratulations, you have done a great job thus far. To remove the flywheel you will need a cheap two arm steering wheel puller and two long M6 bolts with washers. It looks like you have already removed the two dome headed screws from the flywheel that only exist to protect the threads that you will use to attach the M6 bolts. Getting the center bolt on the puller to sit on the end of the crankshaft is difficult owing to the end being machined for the oil pump, I found it easier to slip a 1/2 inch socket over the crankshaft to act as a steady. Before you do all this I recommend that you soak the crankshaft with PB Blaster or similar and let it sit awhile. Now with the puller attached start to wind the center bolt to pull the flywheel off. This will probably be difficult as the flywheel is rusted on there so try some more PB and also with tension on the puller tap the center bolt with a mallet to shock the flywheel. At some point you will hear a tremendous crack and assume the puller has snapped, however it will in fact be the flywheel coming off. Either stuck in the flywheel or on the crankshaft will be the woodruff key, don't loose it.

Now as you look inside the crankcase you will see the trigger for the ignition which is known as the pulsar. Take a scribe and mark a line on the bracket to show where it was positioned and remove the two bolts, now you can remove the pulsar.

Undo the 5 long bolts that hold the crankcase halves together and gently pry the apart. Do not be tempted to put a screwdriver in between the halves as the seal there is very important and can be damaged. You should now be able to pull the halves apart and wriggle out the crankshaft. The bearings (two on the clutch side and one on the flywheel end) should be on the crankshaft but if it is worn might end up in the crankcase.

When I restored mine I purchase both the top and bottom end and that is a decision I never regretted as basically you end up with a new engine, you can find these kits for ~$350. The complete kit comes with crankshaft seals, the top end only does not however you already know that your seals are shot and must be replaced.

When it comes to rebuilding you should thoroughly clean the crankcases. Do not put them in the dishwasher, it does a terrible job and leaves a nasty oily residue that lasts slightly longer that the time your significant other refuses to speak to you. You should use some oil resistant mastic on the two halves, I uses Mega Grey largely because it matched the color of the cases and made clean up easier. As a slight aside I now regret that I didn't paint the crankcase when it was apart as I think that is a sharp look so you might want to think about that.

If you do buy the complete kit you will have to press the bearings onto the crankshaft. They are an interference fit and need to be pressed. You will hear stories about how you should put the crankshaft into the freezer to contract the metal and place the bearings in the oven and so on. Save yourself some grief and find a small engine shop. They will press the bearings on, be done in 5 minutes and charge you $10 or so.

When I rebuilt mine I wrote a blog about it mainly so my offspring who are all over the country could mock me mercilessly (which they willingly did). There are some pictures there that might help so have a look if you want, the address is below.

If there is anything else you need just shout I will keep an eye on this thread.

Good luck

Dave

[TexasHunter]

Dave- Thanks for the quick reply and coaching. I will be working on this today and will take pictures and provide an update on my progress.

[TexasHunter]

I got the fly wheel removed using a cheap puller kit that I bought from Harbor Freight for about $13. I got the crank case separated and dropped off the new crank at a small engine repair shop to have the bearings pressed. I will pick it up on Monday. Here are a few pictures of the fly wheel pulling process. Thanks for the help so far. I am sure I will have more questions as I progress.

[TexasHunter]

I noticed that the fan has a cracked fin. I have looked around and not been able to find a replacement one to buy. Any idea where I can find one to buy that does not have a broken fin? Is this mission critical and something that will cause a big problem if I am not able to find a replacement?

[Dave Box]

If you can get another one fine, but it is not going to hurt you. The fan will still push enough air across the head. Far more damage will be caused by letting the fins get clogged up with mud and debris.

Dave

PS Great job with the flywheel. I look forward to your updates

[TexasHunter]

I received the crank shaft and case back from the machine shop where they pressed on the bearings and re-sealed the case . I had to re-arrange some of the bolts connecting the case so that I could instal the black bracket that connects to the assembly holding the starter generator.

Lesson learned:

• The bolts connecting the crank case are not the same length
• I snapped one of the bolts when tightening it too much
• Be careful not to put to much pressure on the bolts when connecting the crank case

I consulted with a neighbor who is handy with engines and he helped me crack open the crank case, remove the broken bolt and re-seal the crank case using his press.

I completed the rebuild with the upper unit and reinstalled the engine with high hopes that I would have it running the next day.

No Luck- When I press the gas pedal, I heard a clicking sound so I put a booster on the battery to use while trying to get the engine to start. With the battery charger assisting, I am able to spin the engine and it fires intermittently for about 15 pops and then backfires. Also, the stater generator got stuck cycling when I let off the gas pedal. An additional problem was I had gas pumping out of the exhaust pipe where it connects with the muffler.

I read in the other threads and cleaned the connection points on the electrical connections including the micro switch and made sure the ground was clean and it is no longer getting stuck. Also, I changed the fuel pump and no longer see gas coming out of the exhaust pipe.

Now I need to trouble shoot why it is running intermittently and backfiring. Should I go ahead and change the micro switch and solenoid?

I felt excited after completing the engine rebuild but all these other problems are giving me real challenge to solve. Any thoughts or guidance would be appreciated.

[Dave Box]

The first thing that always comes to mind is did you put the piston in the right way around? The port in the piston skirt must face the inlet side. If that is good then we can continue.

Dave

[TexasHunter]

Hi David,

Thanks for the response. I pulled the exhaust pipe and looked at the piston as I manually spun the crank. There was no port showing on the piston from the exhaust side so I think it is installed correctly.

So far I have:

• installed a new fuel pump
• took off the carb and cleaned all of the ports - thanks to whoever posted the diagram on another thread - it was pretty straight forward
• Installed a new fuel filter

[/LIST]
The jets did not appear to be clogged. When I tried to start it again after cleaning the carb it had the same symptoms.

The starter generator is spinning fine but I do still hear some clicking. It will fire a few times intermittently and then just backfire. Could it be a problem with the reed valve? When I put it back together I believe there was only one way that it would fit. Is it possible that I could have installed it in the wrong direction or that the reed valve may be the culprit?

I wish there was a way to post a short video to demonstrate as that may assist with helping me troubleshoot. The amount of beer consumed during this project is quickly rising. As always, thanks for your help!

[racin161]

Is the pulsar plate installed correct ?? Did you mark it when you took it apart and reinstalled It on the marks?? Also make sure the wires from the pulsar didn't get pinched when installing the engine in the cradle I say this because I did it Just my $.02 It does sound like a timing issue.