Starting another new chainsaw project

[Karla]

Completely dissassembled the engine today and the entire chainsaw, so I can give all the parts a thorough cleaning and Inspection. Here are the measurements of the new and old piston & piston ring measurements.

Checking Piston ring wear:

1. Check piston diameter at lowest portion of piston skirt (Use micrometer to measure diameter)

2. Check piston ring side clearance (Use feeler gauges and check clearance with ring installed in piston groove)

3. Check piston ring end gap (Use feeler gauges and check cylinder with piston removed but piston ring only installed into cylinder aprox. ½ inch from bottom cylinder edge)


New Piston & Piston ring measurements:

1. Piston diameter = 1.696 “ or 43.0784 mm

2. Piston ring side clearance = .06 mm

3. Piston ring end gap = .05 mm

Old Piston & Piston ring measurements:

1. Piston diameter = 1.692 “ or 42.9768 mm

2. Piston ring side clearance = .03 mm (tighter clearance due to carbon in ring groove)

3. Piston ring end gap = .23 mm (significantly larger end gap due to piston ring wear)

I will have some pictures of the old piston, on my next post. The old piston really doesn't look too bad, however it did have several good score marks on the piston on the intake side, no scoring on the exhaust side (really clean on exhaust side bur one carbon rub mark). The piston score marks align themselves directly with the piston groove locator pin on the intake side. I have heard of those little locator pins coming loose and scoring the cylinder but can't see how it could score the piston. The scoring marks go all the way from the bottom of the skirt, thru the piston ring, and to the top of the piston. I checked the inside of the cylinder but do not see any corresponding scoring marks in the cylinder wall. I will check the cylinder again tomorrow when I start cleaning up the parts. There is some varnishing of fuel oil inside the cylinder transfer channels but I have not removed the transfer channel covers as of yet, maybe tomorrow. Oh all of the chainsaw parts look good so far but everything really needs a thorough cleaning, The brake handle does have about 1/2" crack thru one side of the handle but can be easily repaired. Maybe I will epoxy that tomorrow too, and then it wil be onto reassembly. I also verified that the fuel tank vent is connected to a vent line that goes to the air cleaner. One of Husqvarna's recomendations were to disconnect the vent hose, unplugging it from the tank vent, and then plugging the vent hose, or buy the special replacement vent hose. Again Not sure how this recommendation will fix a Hot start problem ? All of the bearings look good, and probably won't separate the crankcase or remove the crankshaft, it looks like everything is sealed up good with No leaks. I did remove the flywheel, clutch, and oil pump so I could check for leaks and they really needed a cleaning anyhow. Lol.

 

[Karla]

OK, Here are some pictures of the old piston removed from a Model 545 today, see attachments.

 

[Karla]

Just finished cleaning all the parts today, and yes there was a very lite scoring on the intake side of the cylinder which matches the piston, so maybe that piston ring positioning pin did come loose, and caused the problem. I am going to install a new piston, and piston ring anyway so it really won't matter, but I did try to get that locator pin to move but it doesn't however maybe with a little heat the pin came loose. I can't find anything else that could have caused the scoring. Anyhow, I can hardly feel the scoring on the cylinder with my finger nail they are really very lite marks, so I will probably take some scotchbrite, and just polish the inside of the cylinder a little bit. Oh, also fixed the crack in the brake handle with some super glue and sandpaper, and it definitely feels secure and hardly noticeable. Hooray. Anyhow next step is to start re-assembling everything, I did check the crankshaft bearings and they are nice and tight, no movement, also even before I cleaned the bottom of the crankcase, It was really clean, so it should be a good re-build.

 

[Karla]

I honed the cylinder with some scotchbrite, and it really came out beautiful, it looks like brand new, I used a piece of 1 1/4" OD heavy wall plastic conduit with the scotchbrite wrapped around it, and just kept turning and turning the cylinder onto the wrapped piece about a hundred times. Then chemical cleaned the cylinder, followed by washing and rinsing, and finally blown out with compressed air. Also chemical cleaned the exhaust port, and there was actually a thicker layer of carbon in the exhaust port then I originally thought, It may nave been a 1/16" layer all away around, now its back to just clean metal, so that should help the engine alot. Today, I had lots of errands, so no time to work on my engine today. I need to clean the fuel and oil tank that will be next along with checking and cleaning all the hoses with a pressure test to make sure there are No leaks, also have some hardware to cleanup, I usually put them in an ultrasonic cleaner, which really cleans them up geeting all the stuff out of the Metric allen socket heads, which get filled up with stuff. There was a lot of really fine sawdust and oil, all over this chainsaw, Even the ignition coil was packed full. The previous owner must have been making alot of sawdust, it seemed like a soft wood too, maybe pine or something, anyhow No big wood chips just lots of sawdust, I wonder what his chain looked like or If he ever sharpened it. Lol.

 

[Karla]

My Husqvarna 545 project is back together, I finished it today, except I need torque the cylinder bolts and muffler bolts, and I ended up rounding over my Long 4 mm ball allen socket, I think it just got too worn ( Note: I use that size alot, also was not a good quality.)Anyhow I have a new one on order and much better quality, I like the ball head allens for get bolts out at an angle. My old 4 mm long allen, I will probably just cut the ball end off and make it a straight long socket allen. Also need to run some tests on the chainsaw, like compression etc. before I run the chainsaw. In-addition, I may remove the carburetor one more time because I was not real happy on how it seemed to fit together between the air filter holder, and induction manifold, Its way too difficult to see in the carb compartment once you get all the parts and pieces together in the carb compartment, Lol. Anyhow, another day it should be running, and I wish I had a way to clear and reset the autotune carburator. I have the diagnostics and that woks fine but can't do resets or check for carb updates, which I would have to get from Husqvarna or a Dealer. I did put a new power mate sprocket on the drum, the old one was fairly worn, and since I am putting a new bar and chain on the chainsaw, i decided on a new sprocket, they are fairly reasonable anyhow. If anyone has any thoughts about doing autotune resets or carb updates, please let me Know ?? Thanks for any comments in advance. I will try to get a picture posted in the next day or two of the finished Model 545, definitely pretty, I hope it will cut some wood. Lol.

 

[Karla]

Oh, I have also asked a local Dealer If he would reset my carburetor, and check for any updates. He said he would probably need the whole chainsaw, which he is Not going to get. Because I know the game there, he will hold onto my chainsaw forever, and then tell me the chainsaw needed a tuneup, and charge me some awful labor charge, and I just rebuilt everything myself. Also I know for a fact that all he needs is the carburetor, which plugs into the diagnostic box, so he said he is not sure he could do that, Lol. I am not sure how a dealer cannot know, that all he needs is the autotune carburetor, arrrgh.

 

[Karla]

Finished - Completed my Model 545 project, and No hot start problems either. Lol (See)

 

[Karla]

Oh, final results are in-conclusive as to what caused the original hot start problem, but here are the things I fixed and its a 2013 Model 545 chainsaw:
1. Rebuilt engine, cylinder was Ok but replaced scored piston & piston ring, improved compression. changed from 110 to 130 PSIG
2. Cleaned exhaust port, some build up of carbon but not excessive, now its bare metal clean.
3. Disconnected fuel tank vent line from fuel vent as recommended by Husqvarna ( Recommended to improve Hot Start problem) & plugged vent line which goes back to carb compartment,
4. Replaced Power Mate drive sprocket, which had nothing to do with Hot Start, it was just worn and Installed new bar and chain.
5. Found after both 2nd & 3rd start, decompression valve was not closing after chainsaw started, first start it was fine after re-build. Ordered a new one and will replace, also thought about just plugging it.
6. Replaced Spark plug, cleaned air filter, and replaced fuel filter which I would have done anyhow on just a tune-up, so not sure If this made an improvement for Hot start problem.
7. Ran diagnostics again after rebuild, and after cutting up several logs and testing loading on chainsaw, RPMs' =13,528, got the saw good and hot, and checked re-start with No problem. one pull started.

Anyhow my forensic diagnostics are incomplete and Inconclusive, the outside ambient temperature is fairly cool today (60's F. degrees), so not sure when it gets up into 80-90 degrees summer days, If a Hot Start problem will occur. I will have to wait for next summer. In the meantime I have a nice running chainsaw. Lol. Does anyone have any thoughts of what caused Original "Hot Start" problem as described by original owner ??

 

[barton174]

Did you say you vacuum tested it? I'd be a little leery about the cranks seals being the reason it smeared the piston last time.

Mike

 

[Karla]

Mike,
Yes - I did a before and after rebuild pressure/vacuum test with mighty vac tester and No seal leaks or cylinder gasket leaks. That definitely looked good, also the bearings were good too. But thanks for the thought, I am curious after a little more wood cutting with the saw, I will take another set of compression readings, I expected a little higher number on compression. However my Other Model 545, which is brand new, and about an hour of use has a compression of 110 psig, So Not sure and they both run great, start great, have high WOT RPM's and loaded RPMs. I did cut a little wood today to heat the saw up and see If I could get a change with the autotune settings but really Not much, about the same. So still Puzzeled with what could have been wrong with this chainsaw ?? Oh, I just did another couple of starts since its almost evening and its colder outside, It started in a couple pulls, but after running for a minute, I shut it off and started again, and almost flooded the engine so it seems like it may be easy to flood, I could pull the carburetor again, and lower the metering lever a little inside the carburetor or maybe replace the fuel metering needle, but I think I will just give it some time, and cut up a few trees with it, and see how it runs. I really don't need the chainsaw, I have tons of them and my forensic diagnostics is just a hobby and want to know more about these engines, Lol.

 

[Karla]

Here are the after re-build diagnostic tests, still wish I could reset the original numbers, especially like start times, and number of hours run, and of course the error codes:

 

[barton174]

On your compression, are all of your 10mm plugged saws showing low compression? I ask because the (not the same brand) adapter for 10mm spark plug threads that I got for my compression tester has some more air space in it, before the check valve in the tester, so it reads like 110psi, as well, on my 550XP.

Mike

 

[Karla]

Mike
Yes, I think your onto something, maybe it is the adapter. I have two 545's and one 550, and yes they all read 110 PSIG, After I replaced the piston and ring the reading went from 110 to 130, but maybe I put the adapter in tighter. Do you have a fix, or Is there a better way to do the compression test ?

 

[Karla]

Mike,
I don't think I would want to put any thread compound or teflon tape on the threads which could end up inside the cylinder but I could use some silicone tape around the outside of the fittings, except for obviously the 10 mm fitting. However thinking about it a little more If there was a compression fitting leak then wouldn't the reading bleed off over time, once I get the compression reading after about 6 pulls, the compression PSIG is maintained until I press the pressure release or disconnect the quick release fitting, so Not sure how it could be a fitting conection.

 

[barton174]

It's not a connection/sealing issue, it's likely the adapter that adds air space between the combustion chamber and the check valve, which is exacerbated by the small displacement of the 50cc saws. The more air space between the cylinder and the check valve, the less compression it will see. The check valve, ideally, needs to be right at the tip of the fitting, but with an adapter, it's not. Mine is worse by the adapter not being one that came with my compression tester, so it has a big air space in it, when the tester is threaded into said adapter.

Mike

 

[Karla]

Mike,
Thanks for the Info, and now I have something else to think about. Lol

 

[Amp4027]

Great thread Karla! Very informative and thorough.
Mike does have a point, my brand new MS193T would only read ~85psi, but seems to run pretty good. A used ms200t I bought came in at ~70psi. For my gauge, it seems 90psi translates to new, and 75psi for used (or maybe both my saws are just crap lol, been thinkin the 193 doesn't have much power as the 192... the ms200t spits wood just fine though.) A 20psi jump on a leaky gauge would probably translate to +40psi on a proper one, and for a shine n new piston/ring that is great!
As for getting a good seal, they make soft-plastic nickel-sized washers for plumbing and whatnot, which is what I was considering adding to the brass adapter in place of the o-ring. Just remember whenever removing the spark plug, to air hose it, then undo it one turn and give it a swift blast of non-chlorinated brake parts cleaner or starting fluid (don't use carb&choke cleaner - it can make the plastic housing very brittle) from 4 angles to get out any dirt or wooddust so all your hard work was not for naught.
Really though, to get a real compression reading it is as Mike said, the schrader valve needs to be right at the tip of the adapter. As for doing that, I am not sure what size tap and drillbit is needed.

I can't find anything else that could have caused the scoring.

My bet would be the piston ring itself from looking at the last pic - the very ends/corner of the ring look chipped off, esp the left side. Piece prolly stuck itself to the cyl wall while the piston traveled a few times until it made it out the exhaust, hence no scoring on the cyl wall but a groove down the piston side.

You wouldn't happen to be from FL, would you?

 

[Karla]

AMP4027
No I'm Not from Florida, I live in NJ. I do buy alot of parts from FL. LOL.
Thank you for the information, I guess its really more of a curious question, as to what is the real compression numbers, but as long as it starts in a pull or two, and runs at the correct RPM's both in Idle, and when cutting, then its probably a mute point. Except for troubleshooting and knowing where the numbers really are for comparison. So just as a curious factor I will probably check the compression again the same way when I get several hours on the chainsaw and see If it increased. But won't know the answer to that for a while. I do have a couple of nice size Oak trees that need to come down and get cut up for firewood. I lose a couple of trees every year, so in the fall its time to start cutting. My Oak trees are about 20 inch diameters at the trunk and 70 ft tall, so they are good size trees. I also only have a couple of acres of fairly heavy wooded property, but I do have lots of friends who always ask If I could cut down some trees for them. Too funny and I do have some very particular requirements for cutting a tree. Near power lines definitely No, Near a home, building or something I could break, then No, If I could get hurt then No, If its out in the middle of woods then definitely Yes. If its barber chaired or in a very precarious position then probably No, but with one good friend to help then probably yes. Anyhow I enjoy cutting wood, and do burn quite a bit in my glacier bay wood stove thru the cold winter. anyhow, just some FYI.

 

[Amp4027]

Those are good safety practices. You don't want to cut a tree that is Bo/Beau'd out. There is someone selling a older 338XPT that I was going to take a crack at, but just don't have the loosechange for it atm. Curious, why Husky? Is the AutoTune just something that you like better than Stihl or Echo equipment?

Just some knowledge I came across here which I wouldn't of thought of: (just take it at facevalue and always verify on your own accord)
If the saw RPM increases when it is turned to one side (left/right), then there is a air leak on the opposite side seal.
An air leak will not always present itself, be sure to rotate the flywheel slowly or set it at different positions when vac&pressure testing. ie: slightly egged/worn or bent driveshaft from chain being overtightened or not loosened after a hard days work and contracting while cooling (dealers are always cranking that chain out to near over-tension when you buy it and never advise you to loosen the sidecover & chain tensioner at least 2 turns after running it)
If it increases or decreases when tilted forward/backward, it is from excess fuel that has pooled in the crankcase bottom and is riding the piston bottom and getting sloshed around, or the piston rings have a slight leak and the fueloil itself is creating the compression seal.
Increasing oilmix from 50:1 to 40:1 actually makes the air/fuel mix -leaner-, not richer&cooler (even though just slightly, something like 4-7% change by volume).
According to a handful of repair techs on here, 50:1 with "modern" 2-stroke oilmix is supposed to be sufficient, but machines ran with 40:1 come into the shop showing less mechanical wear. Personally I think the 50:1 is an EPA shenanigan, just like ethanol gas.
How the fuel filter is positioned in the tank can make a saw run great or near un-tuneable. ie. if it is vertical, then it gradually gets leaner and leaner until the tank is empty, due to air getting sucked in with the gas as the fuel level goes down.

 

[Karla]

I believe that to be true, and I have a friend that owns a repair shop for Jonsered Chainsaws for about 40 years, and use to be a Homelite dealer, On occassion when I'm all done with my rebuilds and I want a second opinion on whether I have cured all the Ills of the chainsaw, I will bring one to him. He always cranks it up right away when i walk in the shop, and goes thru the left/ right/ up and down gyrations, and really listens to the saw. Then he gives me his honest opinion that I did good, and I have a really nice saw. My own experience, and never ever charges me for listening to it (A really sweet deal). I always pull the clutch & oil pump, and also the flywheel and take a physical look at the seals, and if I see any kind of wetting or stain like fuel was there, then I know I probably a seal leak, then everything gets uber cleaned and sometimes I will put some WD-40 oil in the crank case just a couple of ounces, and lay the saw on that side, and see if there is any weepage thru the seals. I use the oil because I also rotate the crankshaft, and clean the bearings with the WD-40. Then clean the crankcase all out looking for any debris. I also pressure/ vacuum test almost all my chainsaws that I work on, it really only takes a few minutes to test. Fuel, Air and mixture ratio's - I always believe in testing the chainsaw to the manufacturers' Specs, so if they recommend 50:1 and built the chainsaw both design & tested, then I want the same engineering results, or at least close to it. I believe in always when you first pick up your chainsaw, if it has been previously fueled to give the chainsaw a little shake to insure the mixture is still mixed, same with my fuel fill can, I give it a little slosh before re-filling my chainsaw. I have never had a problem from a scored cylinder of my own, or personally owned chainsaws, including my oldest chainsaw a 1982 Homelite Model 330, which runs like it is brand new. Also I do believe in keeping a chainsaw very clean, clean it up before and after use, and sometimes when stopping to sharpen a chain, give it a quick cleaning then too. I think one of the culprits is too much heat and any dirt that restricts the airflow around an engine just can't be good. Lol. Anyhow, thats my two cents, or maybe a nickles worth. Lol.