2 stroke rebuild


Old 05-09-04, 10:06 PM
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Question 2 stroke rebuild

This may not be the right spot to pose this question, but this web site did wonders for me back in October. Here goes: I've got an old McCullough Mac 2818 gas string trimmer and the darn thig won't start or run. I've replace all of the fule lines and even the in tank fuel filter, but it won't fire. I checked the forum yesterday and a couple of folks said that there could be exhaust blockage. When I pulled the carb, to soak in parts cleaner, and the one cylinder off of the engine, there was tons of carbon build up. Granted this trimmer is some 10-12 years old and has never had the engine rebuilt. I've soaked the cylinder and piston in parts cleaner and got them both looking pretty darn clean . When I tried to remove the piston ring from the piston, it broke in half. Now I know I'll have to get a new ring, my main question is: Is there any "easy" way to re-install the new ring on the piston and then push the piston back into the cylinder bore. I talked with a manager at a local parts store that I used to work at and he suggested using a well lubed hose clamp to compress the piston ring due to the fact that a normal automotive ring compressor would be too big to work around the cylinder bore. I intend to goop the hell out of the clamp with weel bearing grease then re-install the piston. If this is a suitable way to aproach my dilema, I'd love to hear some feedback on the issue. If not, can someone direct me down the correct road. By the way, once this thing is put back together, I'll hop online and give the results.
Thanks to all.
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Old 05-09-04, 10:34 PM
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Hello Heidelbrg!

The clamp will work well. I guess wheel bearing grease won't hurt, but It s bit more than necessary. Some white lube or heavy-bodied oil would work fine. No need to get it all goopy, just coat it.
Old 05-09-04, 10:43 PM
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Thanks Cheese. I'll try just using some white lithium grease.
Old 05-10-04, 05:31 AM
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Hello Heidelbrg.

An oil additive works well to lube the cyclinder walls, piston, rings and bearings during reassembly. I use to use STP during assembly and it worked well. Not too much. Just enough to coat the parts, than wipe off excess.

Next tip is to ensure moving parts infact do move once assembled and prior to installing the cyclinder head and lower end, etc.

Use a light oil on the corners of metal surfaces where gaskets are placed. Doing so aids to insure they stay in place during assembly. Also helps to insure no vacuum leaks will develope during reassembly.

2 cycle engines cannot have a vacuum leak in the crankcase. If one does exist, the engine will run very lean and overheat. Reassembly must be done correctly to insure no vacuum leaks exist.

Reassembly of the piston into the cyclinder bore can be done with a hose clamp but in some cases not always an easy task. A local small engine repair shop should be willing to reinstall such for a tiny fee and or free. Free is good public relations, especially if the parts where purchased there also...

Carbon removal from piston and head can be done quickly and easily using a wire wheel on a grinder. Be sure to remove the carbon build up in the top of the cyclinder also. Light sand paper can be used, if done carefully, since a ridge rimmer is not lighly available. Failure to remove the carbon can cause problems.

You mentioned carbon build up in the exhaust muffler. No mention of cleaning it or how that aspect was done. Carbon there too has to be removed.

Small engine generic repair manuals are very helpful to the novice. Available at all local small engine repair shops and or lawn mower repair shops in your area. Shops and dealers are listed in the phone book directory.

Regards & Good Luck. Sharp Advice.
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Old 05-10-04, 03:00 PM
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Mac trimmer

By design, the bottom end of the cylinder has a taper to the bore on this as well as most 2-stroke engines. A clamp, of any type, should not be necessary. Just some 2-cycle engine oil coating on the piston, rings and bore (lightly coated) will do the trick along with a small flat screwdriver to work the ring into the landing when assembling. One item to be aware of on McCulloch's: Inspect the armature air gap prior to reassembly...these machines are notorious for excessive gaps. Set gap to .012" and use blue Loctite on the coil mounting screw threads to ensure they don't back out. Loctite is a good idea on the cylinder-to-crankcase mounting screws as well.
Also be sure all the carbon has been removed, by way of chipping away with a small screwdriver, from the ports before assembly.
Old 05-10-04, 04:56 PM
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Good advice to follow,But might I add just one thing to remember.On all 2-cycle pistons there is a line-up pin for each ring.Position ring on piston to where the gap in the ring lines up with this pin.If the gap isn't lined up with the pin,the ring will brake when ever you try to push it into the cylinder.
If needed they do make a 2-cycle ring squezer,just had to order one a week ago.All plastic,made in Italy.
Old 05-11-04, 03:20 AM
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One other item of note

Be sure to clean out the ring landing in your piston. Since you said the ring broke upon removal, this is because there was excessive carbon build up in the landing which made it difficult to remove. Do you have a source for parts for McCulloch? If not, I can supply you with a gentlemens name and number.
Old 05-11-04, 07:43 AM
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Lightbulb Potential Parts and or Manual Sources

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I do not have any affiliations nor vested interests in any of these retail parts suppliers above. Provided solely to assist with locating parts.
Old 05-14-04, 12:42 PM
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Engine rebuild

I had a quick question for the moderators. I am rebuilding a Stihl FS-36 grass trimmer. I've run into a problem with the starter. The pull starter will lock down on the engine casing after a couple of pulls. I'm not sure how to adjust the pull starter to fix this. Any suggestions?
Old 05-14-04, 04:22 PM
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re: ring compressor

Hello Heidelbrg:

Ring compression tools of a size suitable for your rebuild run from $6 to $8 USD and make the job a lot neater and easier.

If you can't find one locally there are many sources on the net.

Repost if you get stuck and can't find one.

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