Loctite 572 and question re crankshaft "attachment..

[TownsendsFJR1300]

Took apart a customers "locked up" Echo CS355T chain saw today.

Looking at the below pic's, what happened is a "plastic piece" (apparently 2 attached to each side of the crank), one let loose- NO damage to the rest of the engine, metal (with loops) stayed below.

Masking tape on the first pic shows the undamaged part. Carnage from the broke one is pictured below (same pic)

I have never seen this arrangement on any two strokes and the parts diagram for a replacement crank does NOT show them.. I suspect it's to cut the lower end air volume down, thoughts?

Remove the other and ??? Their not weighted, just don't want to spend 3 hours re-assembling for crappy performance


Also, re-reading 99Yams rebuild thread, Loctite 572 is good for the lower crankcase half's? Max RPM's are about 13,000.

Thanks ahead of time...

[99yam40]

I have never seen anything like that before attached to the crank weights.
I have not had to tear apart an echo chainsaw before, even tho I have a CS3400
do you think it got too hot and melted?

what is that metal loop and where did it come from?

might need to head over to a saw forum for this one

[panasonic]

I don't know about the crank...never seen that before either. Really don't have much choice now but remove the other and see how it works, if you can't get the part.

Loctite 572 is thread sealant. You would be looking for Loctite 518 for crank cases. I would buy Permatex 51813...it's the same thing at half the price.

I use hylomar "aerograde" PL32

[panasonic]

Funny one melted and the other didn't...weird.

[panasonic]

13000 rpm is ticking over pretty quick...but not fast for a two stroke.

I always think of the Yamaha R6 motorcycle...16000 rpm Four Stroke!!! And crazy dependable. It just loves to sing.

[pstephens46]

Seems many of these modifications these days are to reduce emissions. If air is restricted there does it mean carb is tuned with that in mind? Echo is normally good stuff.

[TownsendsFJR1300]

I have never seen anything like that before attached to the crank weights.
I have not had to tear apart an echo chainsaw before, even tho I have a CS3400
do you think it got too hot and melted?

what is that metal loop and where did it come from?

might need to head over to a saw forum for this one

The plastic piece still attached to the crank, there's TWO on each side. That steel loop wire holds them to the crank, NOTHING ELSE...

As you can see, the dislodged hoop isn't bent up much. It is an old machine and I believe the plastic, over time, just failed causing it to fall apart, then got destroyed/melted. Part of that broke plastic embedded itself into the bottom of the piston-stuck between the dome and wrist pin!!

Another piece got THRU the ports and was melted to the head (cylinder and head are one piece). There is NO damage/marks to the top of the piston. Looked like bad casting but poked at it and the melted plastic came off and the cylinder and head are fine.

As noted, in the NEW parts diagram, the plastic pieces don't not show at all on a new crank..


Good idea checking a "saw forum". I'll be cleaning and putting it back together once I get sealer. Tks.

Thanks as well Panasonic for the sealer part #..



*Just one other thing I found (and caused a problem on another, same machine). There's a small brass tube (the size of fuel line-SMALL) that goes in the cylinder (below the piston). This exits out of the block, a small hose attaches to that and then eventually goes up to the intake flange of the carb. ???



Another machine (same model) was brought in, and the workers apparently knocked it off causing the machine to lean out and go to WOT immediately. Took awhile to find that, but once attached (and carb tuned) runs good. Waiting on some parts today to finish that machine (was getting stripped down by workers )

[TownsendsFJR1300]

Wrote another post, waiting to see if the moderator posts it, but


Found this:

Higher crankcase compression is very beneficial in a high speed 2-stroke because the fuel-air charge in the crankcase must be "transfered" up into the cylinder from the crankcase in an incredibly short time. More pressure in the crankcase will deliver more charge in the short time the transfer ports are open.


It's called a "crankshaft stuffer", helps performance especially in high RPM engines. Pushes more air thru the engine. Funny thing is, I can't find it anywhere, Echo doesn't show it, nor anywhere else...

[99yam40]

that port from block heading to the carb is normally just a drilled and mated surface on carb flange on most of the motors I have seen.
If it is ported to below piston then it is just connected to the crankcase, probably using that pulse to move the diaphragm to pump fuel.

I have found pulse ports from crankcase to auto oilers that were run with hoses and when they failed it sucked air and was impossible to start unless you dumped some fuel into the carb and then it would run only at high RPM(died is dropped too low)

[zenoahphobic]

I've not seen this plastic either but I guess, I think as suggested, it has to do with crankcase pressure. That is they reduce the volume of the crankcase, therefore increasing the pressure.

I imagine they did this with very light plastic so as to not alter the crankshaft counterweight balance.

As these are cheap small engines, they probably save costs by not redesigning the crankshaft, and probably the crankcase as it would need to be wider to accomodate a more modern round crankshaft found in new engines these days.

A development thing trying to increase performance of an existing design before needing to completely redesign a new engine.

Makes you wonder how long they expected them to stay in place, as it by reasonable engineering standards, I think can only be regarded as "temporary".

[99yam40]

I've not seen this plastic either but I guess, I think as suggested, it has to do with crankcase pressure. That is they reduce the volume of the crankcase, therefore increasing the pressure.

I imagine they did this with very light plastic so as to not alter the crankshaft counterweight balance.

As these are cheap small engines, they probably save costs by not redesigning the crankshaft, and probably the crankcase as it would need to be wider to accomodate a more modern round crankshaft found in new engines these days.

A development thing trying to increase performance of an existing design before needing to completely redesign a new engine.

Makes you wonder how long they expected them to stay in place, as it by reasonable engineering standards, I think can only be regarded as "temporary".

only needs to out last the warranty period

[TownsendsFJR1300]

I've not seen this plastic either but I guess, I think as suggested, it has to do with crankcase pressure. That is they reduce the volume of the crankcase, therefore increasing the pressure.

I imagine they did this with very light plastic so as to not alter the crankshaft counterweight balance.

As these are cheap small engines, they probably save costs by not redesigning the crankshaft, and probably the crankcase as it would need to be wider to accomodate a more modern round crankshaft found in new engines these days.

A development thing trying to increase performance of an existing design before needing to completely redesign a new engine.

Makes you wonder how long they expected them to stay in place, as it by reasonable engineering standards, I think can only be regarded as "temporary".

This Echo machine is a commercial machine is certainly NOT a cheaply made machine. Stihls and Echo's are what's used commercially by the yard guys
and by far well made. Been working on them (those specifically) for a year and half now (commercial tree cutting account), servicing all his equipment.

This particular engine is old, bought used and run VERY HARD. I resurrected it from the dead about a year ago. That plastic tab, that the wire was crimped around (holding everything together), it doesn't surprise me it failed, 13,000 RPM's, run HARD 5 days a week, for YEARS, plastic goes away/fails with heat, time, etc... My customer has at least 3 of these machines (not to big, not too small) but good for the guys literally hanging in the tree's (35cc's)

I've been working a bunch on Stihl, Shinindawa's (Echos), Echo's and about everything Poulans and cheaper models..

The local Echo shop, as of this am, surprisingly, NEVER saw this plastic part before.

It does just lessen the space in the lower end for better performance (after doing much research.) I'll be leaving the one good one in.


*Yam99, that crank "vent/tube" does go up and thru a very small plastic orifice, eventually end up at the carb mounting surface. With that said, it is THE ONLY machine I've come across that uses a hose for the diaphram carberator. The Stihls (I've come across) don't have it, the Echo trimmers/weed eaters, pole saws, etc don't have it. NONE of the cheaper brands have it. Pretty much rely on fuel expansion from the machines vibration / movement..


It'll run again, just likely slightly lower on power, how much, dunno, but will report back. Waiting on case sealer now(doesn't take much)…

Worse case scenario, it's a "parts machine", which everything but the crank/piston are good. A coil for that machine is easily $40. A carb, well over $100 (Walbro), etc.

Here's a NEW machine (still being produced) for $338 vs a lowes/ HD cheaper model for $100 and change: https://www.rcpw.com/equipment/echo-...MaAu5WEALw_wcB

Anyway, thanks for the input..

[99yam40]

most of the motors I have seen have a drilled passage that runs to the carb flange for the pulse.
but then I mainly work on old non commercial stuff

[TownsendsFJR1300]

most of the motors I have seen have a drilled passage that runs to the carb flange for the pulse.
but then I mainly work on old non commercial stuff

Interesting...

99% of what I work on is usually not more that 10 years old. Abused motors, look worse with a year or two on em...

[zenoahphobic]

By me saying cheap, it refers to all small Two stroke engines, they are cheap to manufacture that is why they are so prolific. I have an Echo chainsaw, 40 years starts second pull, never had a need to pull anything apart on it, so maybe it has plastic spinning within it to. But agree plastic used inside an engine, spinning and rattling would seem to have less of a life than the metal parts.

I would expect you may have running issues if you dont replace that plastic part. Jetting may need to be altered as the airflow or pulsing of air thru the carb will change, there maybe slightly less initial suction available to draw fuel.

Usually the pulse for inbuilt fuel pumps such as Walbro, have a hole through the inlet manifold insulator obviating the need for any nipples or plumbing.