Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Homelite 20042A, 25cc

It was a problem getting the ring in because the bottom of the bore flares out.  You can't use a ring compressor.  I put the top of the piston in the bore then tried pushing the ring in with the tip of a pick.  In the process the ring broke.   What's the way to do it?

Where should the ring gap go?  Is it centered on the longest section of uninterrupted wall?

The crank weight has 11 degrees stamped on it.  How is the timing set?  I have not taken off the flywheel and assume it only goes in one way but not sure.  There is no key shown on the exploded view. 

If this is a two cycle engine, the piston ring groove will have a tiny dowel in it.  That's where the gap goes.  The rings can only fit one way with the notched ends of the ring fitting the dowel.  If that was not all properly aligned when you tried to put it in, that's why it didn't go. 

Regarding the timing.   Many newer engines don't use keyways anymore.   The piston/crank degrees from TDC has to be set by putting a dial gauge in the spark plug hole to measure degrees or mm. before TDC.   However, if you carefully mark the crank and flywheel by using a thin cutting blade on a dremmel, you can mark the crank and flywheel by cutting a fine line across the two surfaces.  That will ensure you have things lined up when you re-assemble.  Otherwise, it's necessary to use the dial gauge.   Good luck and let us know how it goes.  

   Looked at the piston groove and there IS a dowel there and the reason for the no-go.

   This is my first two stroke.  It would not run with gas in the plug or throat.  It would only fire for one revolution and nothing more.  It had a torn gasket on the crank area cover.

Have you got it running?

Pistons with ports in the skirt usually only go on one way.  Generally, there is an arrow embossed on the piston crown that indicates installation direction relative to the exhaust port.  Arrow points to exhaust side of the cylinder.    Another way to figure out piston installation is understanding that the ports in the piston skirt are there for the intake cycle.  Accordingly, the piston skirt ports should also be toward the carburetor side. 

Check out donyboy73.  He rebuilds a lot of chainsaws and other 2 cycle stuff.

http://www.youtube.com/user/donyboy73

trouts2 wrote:

hey trouts...  if the base gasket was torn that would most likely be the reason it wont start...2 stroke need compression on the bottom end to run properly...and crankcase pressure also runs the fuel pump in the carb.

Hey Trouts,

The rear end of that engine is the biggest problem... (the gasket and plastic cover)...

The screws back out of the plastic cover and the gasket leaks... Be shure to use  "perma-tex" gasket sealer on the cylinder gasket and the plastic cover gasket.

I lalso put the Loc-tite on the plastic cover screws too keep them from backing out...

Good Luck,

Friiy

Borat: Have you got it running?

   Not yet, it needs at least a ring and gaskets

 

>>Generally, there is an arrow embossed on the piston crown

   No arrow or mark on the piston.  Maybe it’s not fussy on these models. ?  Which way does the dowel usually face?

Friiy & niper99,

     The compression on this was 70psi which I would think ok for a start and run.  I don’t think there is any compression release on these.   What’s a ballpark psi for these?

 

   The sump area cover gasket was torn and the cylinder gasket in bad shape.  I’m not sure if those were ok before and ripped during disassembly.

 

   One of the screw bosses fell off when the cylinder was unscrewed.  There are only three screws holding the cylinder down, one broken so only two.  There are threads left on the boss so might be enough for grip.  Maybe the boss area could be clamped and glued in place. 

Broken boss lower left.

 

Broken boss lower left

The crank is on roller bearings which was a surprise.

Compression on these small two cycle engines vary considerably.   I'd shoot for at least 90 psi and would be happier with 100+.

The dowel on the piston must line up with a portion of the cylinder that has continuous metal for the entire stroke.  You don't want the ends of the rings catching the edge of an intake or exhaust  port.   Do you have the piece of the boss that was broken off?   If so, you could try some JB Weld to put it back on,then re-tap the hole.   JB Weld is miraculous stuff.  It might just hold if you don't torque the screw too much.

trouts..

ya 70 psi not a good number....it might run with that compression but i suspect with a great deal of power loss.....usually l would like to see 100 psi as a mininum...but l have a homelite myself that has 75 psi and it runs and starts not to bad so they sometimes will run with low compression but usually are hard to start and have no power..and if it has low compression then theres usually alot of blow by past the rings wihich counter acts the crankcase negative pressures...so on the compression stroke (piston moving up) there a negative pressure in the crankcase thus closing the diaphragm in the carb (running the fuel pump)..and on power stroke (piston moving down) the crankcase has postive pressure pushing the diaphragm open alowing fuel through. that why if u have a blowin gasket or worn crank seals they just dont run right or at all....and most times like friily said bolts come loose and that make them run lean which in turn causes scoring of the piston walls and serve piston ring wear.

as for the broken off ear....l would braze it and build it back up...lm a licsened welder so i have some experience in this area...Search on u tube DURAFIX and watch some of those videos u gonna need some pratice though it looks easy but not so much u need to get the hang of it.....l have also brazed about 5 of tecumseh blocks that have throwen a rod and cracked the block, not 1 comeback and one of those was on my 10 hp tecumseh which is still going strong. all u need is aluiminum rod that melts at about 730 deg and a propane/mapp gas torch oh ya and a stainless steel brush to clean the surface before u weld. 

Borat and niper99,

>>>Do you have the piece of the boss that was broken off?  

 

   I do. there’s only a tiny amount of surface to weld to and very difficult or impossible to get at the back sides for welding.   I might try JB weld.  The surfaces are clean, rough (good surface for gluing) and fits back in it’s spot very well.  The surfaces are small though. 

   Possibly JB welding it in place then using a bolt through the crank piece and bolt with a washer on the broken section head side might work.  The washers could grab the remaining ½ not broken section on the head side.  Even if the weld broke the washer would hold the broken head section in place and hold down the head to the block section. 

 

   Thanks for the Durafix reference.  I watched many videos on aluminum welding.  I never knew that repairs could be done with a small torch.  Very interesting stuff.  Poking around YouTube I found stitch pins and a few other methods of repairing cracks in cast blocks I never heard of before i.e., locking pins, tapered, screw-in, and stitch.  I'll probalby give the aluminum welding a try on some scraps.

I'm not familiar with Durafix but it sounds like it might be similar to Alumiweld. That's available at Harbor Freight and also has Youtube videos about it. The cool thing about Alumiweld (it's really brazing not welding, BTW) is if you assemble the thing and then use it, you can disassemble in the future as it won't stick to the steel bolt.

Bill_H,

    They are the same type of rods. 

    I think what you said was if you aluminum welded (low temp braze) around a bolt then the bolt can be backed out as the weld filler will not stick to the bolt.  Just getting familiar with the terms but I think that is due to the wetting action which is the bonding (wetting) of the filler to the welded stock.  The temp of the steel bolt would be higher so no wetting (sticking).  The bolt could be welded around and backed out. 

   There were a few videos of making a threaded stud.  A puddle of filler was melted onto an aluminim piece and a nut placed on top.  The inside of the nut was then filled with filler and when cooled the nut backed off the filler making a threaded stud on the piece. 

    Possibly an experienced person could build up the broken ear with or without a bolt inplace.  If without then the hole could be drilled and tapped or run a nut and bolt through.

     One interesting video had a block put in a oven to get it to 200 degrees then reparing a crack.

   

Bill_H,

   I picked up some alumaweld rods at HF but have not tried to use them yet.

Borat,

    The broken ear on the head was glued with JB Weld.  I let it dry for a several days then tried pushing hard up and down on the ear it's holding.  That's impressive as the two glue surfaces on the ear are very small.   I think it will hold the screw torque and probably be ok when vibrating under load. 

Good to hear you fixed it with the JB Weld.  That stuff is indispensable.  I was at camp for a few days and had to use it several times for an assortment of fixes.  Amazingly tough stuff.

Have you got that little engine running yet?

   No, the ring has not shown up yet.  I'd like to check the end gap when the ring comes in but don't have any specs.  I suppose it does not matter.  If it works fine and if not I keep it for parts.

   I'm just about to order rings for the Toro Powerlite 3hp.  Waiting until I do a bit more work on it to make sure I don't have to order anything else.  That one will be interesting as I've never worked on one with needle bearings and don't look forward to the re-install. 

   Many years ago when I was a kid my farther rebuilt the 7hp Merc engine for our hydroplane.  I remember the needle valves and him having some difficulty with them but he got'em in and the engine ran fine for many years after the rebuild.  It was interesting as he was a drugest and I never saw him work on any engines or OPE before or since.  His interest was woodworking but he would tackle anything and usually pull it off. 

   The ring came in and installed.  On screwing on the head the glued ear broke off.  The ear section contained half of a screw position.  I think the mate of the ear to the rest of the head ok but when screwing in the screw the ear broke.  It went in with resistance.  There was probably glue in the thread area and caused too much pressure on the ear.  The other head screws were put in and the section by the ear covered with glue along with a large section of head to crank.  Glue now runs from the head through what’s left of the screw hole over to the crank section.  The glue section then is massive and covers the head and crankcase area.

 

   It starts and runs so if the glue and the other screws hold the head in place it should be a viable engine.  I’ve got a trimmer with the same engine so will probably swap them and keep the original as a spare.  The engine had very low compression and now gets 120psi.   The purpose of messing with the engine was just to get experience with two strokes.