Crappy tach seized my mom's saw

[jacrawley]

I just fixed my mom's husky 235. It just needed a little carb adjustment. I bought one of those wired tach with the hour meter for 15 from the local parts store to set the h screw and today I get it back with a seized motor. I checked the gas and it was definitely mixed. Has anyone else had a problem with those cheap tachs? I feel pretty bad about it. Is there something else I can get between the cheapest and the $90 models that are reliable?

 

[LonestarStihl]

I just fixed my mom's husky 235. It just needed a little carb adjustment. I bought one of those wired tach with the hour meter for 15 from the local parts store to set the h screw and today I get it back with a seized motor. I checked the gas and it was definitely mixed. Has anyone else had a problem with those cheap tachs? I feel pretty bad about it. Is there something else I can get between the cheapest and the $90 models that are reliable?

Stihl EDT9 is about $60

 

[alexcagle]

What perameters were you shooting for to set the "High speed" adjustment?
If you were unknowingly enrichening it to compensate for a clogged internal carb screen, a plugged fuel filter, or an inoperable tank vent, it can still end with a lean siezed piston.

 

[jacrawley]

I don't remember the specific rpm. The saw had very few hours on it. Perhaps it had another problem. I'm a little freaked about using the tach on anything else. I looked the rpms up on the interwebs

 

[alexcagle]

I don't remember the specific rpm. The saw had very few hours on it. Perhaps it had another problem. I'm a little freaked about using the tach on anything else. I looked the rpms up on the interwebs

There are a few threads on here on the best way to set the High speed mixture.
key word "four stroking" @blsnelling has several that are easy to understand.

 

[Big_6]

Great saw!
2600 L 12500 H
Did you trim the limiters?

Sent from my SM-G900V using Tapatalk

 

[rmh3481]

At a preset top speed <rpm> the ignition module starts to drop spark. Lets use 14,200 rpm as an example. Once the ignition module reaches 14,200 rpm, it dumps spark to ground in an effort to save the engine from over speeding. So here you are trying to set the high side and the ignition is dropping spark on you giving the illusion that the carb is set rich enough. The result is actually too lean.

Most small two stroke engines are now coming with these digital ignitions which help with warranty claims and air pollution requirements. Thank the EPA.

Only way around the ignition limiter is to either tune under load which takes 3 hands, or set to a specific no load rpm. The no load top rpm is published in the service manual. You will need an inductive tach made for the application to set to the limit.

Oppama makes the Echo and Stihl tachs of you are looking to buy one.

 

[Okie]

I use a tiny tach tachometer made by echo, has a very fast refresh rate and can replace the internal battery by removing some small screws on the rear of the unit, (some tachs do not allow for internal battery replacement) cost about $50 BUT

to get to the bottom line of a chainsaw overheating and seizing, NOTICE that I did not mention carb being adjusted lean because other things can cause overheating and seizing I started using a 3M infrared thermometer and monitoring the jug temperature while the saw is into a heavy full bar cut with a sharp chain.
I first use the tach and set the carb H jet so as the saw is 4 cycling slightly rich and not over reving on the tach, then take the 3M and the saw to a large log for a full bar cut load test and load the saw full bar with a sharp chain and monitor the saws jug temperature. If all is well the temp will not exceed around 375 degrees, if it starts getting to 400 and doing so fast the block/piston is overheating and the saw is going to sieze due to the piston swelling and scrubbing. A helper is handy for aiming the thermometer while saw is in a full bar cut with a downed log but if chain is sharp the saw will load itself and helper not required.
Might not be a carb adjustment, might be fins clogged, seals leaking, carb leaning out due to other things.
You can also adjust the carb H jet to lean and load the saw and see the temp rise fast and the engine is below factory rpm specs when in the cut. (overheating due to running lean, but not exceeding spec'ed max) rpms in the cut.
excess Mixed gas (rich) hitting the piston is what is keeping the piston from overheating.

Anyway: The infrared thermometer lets you know that things are not going well immediately BEFORE the meltdown and a tachometer won't always let you know. Just because the engine is not overrevving (rpm's too high) does not really mean that it's not overheating or going to eventually overheat and the infrared gives you an immediate heads up that temp is headed for the critical zone.
I'm constantly reaching for the 3M doing heat/AC tests and checking cylinder exhaust temp tests on Auto engines to see if the cylinders are balanced and confirming engine block temps.

 

[Sepia]

I've seen people mount tachs on their saws - why not mount a temp monitor?

 

[Khntr85]

I have a hardline (I believe) tach/hour meter.....these are in NO WAY made to be strictly used as a tach, the refresh rate is way to slow!!!


I got mine strictly for the hour meter.....the Stihl tachs have a much faster refresh rate!!!

 

[blsnelling]

There are a few threads on here on the best way to set the High speed mixture.
key word "four stroking" @blsnelling has several that are easy to understand.

http://www.arboristsite.com/community/threads/chainsaw-tuning-101.250802/

 

[82F100SWB]

I highly doubt the tach had anything to do with it. Have you pulled the muffler and looked at the piston yet?
The last seized 235 I had was a bent piston skirt on the intake side from a loose piece of casting flash. No visible damage until I pulled the jug.

 

[Okie]

I have a hardline (I believe) tach/hour meter.....these are in NO WAY made to be strictly used as a tach, the refresh rate is way to slow!!!


I got mine strictly for the hour meter.....the Stihl tachs have a much faster refresh rate!!!

My tach which has a very fast refresh rate is a Echo pet 304 and is about 5 years old.
You will have to do some searching to see if it's available or been replaced with a later model and the best prices.

jacrawley:
If I were you with a seizing saw I would go with the IR thermometer first probably.

I also think You need to remove the muffler first and take a peek at the piston ASAP before continuing with adjusting and testing.

 

[Okie]

I've seen people mount tachs on their saws - why not mount a temp monitor?

That seems like a no brainer, but a permanent temp or tach mount onto my chainsaws would not be user friendly or survive for very long the way I work my saws.
Also seems most users think that temp is directly related to the rpms, which is not the case if the saw is loaded in a cut and running lean.

 

[Sepia]

I was kinda wondering if temperatures under load are a better tuning indicator than rpms or sound? Agree not very practical for permanent mounting, and would be slower tuning than using a tach or trained ear.

 

[alexcagle]

I use a tiny tach tachometer made by echo, has a very fast refresh rate and can replace the internal battery by removing some small screws on the rear of the unit, (some tachs do not allow for internal battery replacement) cost about $50 BUT

to get to the bottom line of a chainsaw overheating and seizing, NOTICE that I did not mention carb being adjusted lean because other things can cause overheating and seizing I started using a 3M infrared thermometer and monitoring the jug temperature while the saw is into a heavy full bar cut with a sharp chain.
I first use the tach and set the carb H jet so as the saw is 4 cycling slightly rich and not over reving on the tach, then take the 3M and the saw to a large log for a full bar cut load test and load the saw full bar with a sharp chain and monitor the saws jug temperature. If all is well the temp will not exceed around 375 degrees, if it starts getting to 400 and doing so fast the block/piston is overheating and the saw is going to sieze due to the piston swelling and scrubbing. A helper is handy for aiming the thermometer while saw is in a full bar cut with a downed log but if chain is sharp the saw will load itself and helper not required.
Might not be a carb adjustment, might be fins clogged, seals leaking, carb leaning out due to other things.
You can also adjust the carb H jet to lean and load the saw and see the temp rise fast and the engine is below factory rpm specs when in the cut. (overheating due to running lean, but not exceeding spec'ed max) rpms in the cut.
excess Mixed gas (rich) hitting the piston is what is keeping the piston from overheating.

Anyway: The infrared thermometer lets you know that things are not going well immediately BEFORE the meltdown and a tachometer won't always let you know. Just because the engine is not overrevving (rpm's too high) does not really mean that it's not overheating or going to eventually overheat and the infrared gives you an immediate heads up that temp is headed for the critical zone.
I'm constantly reaching for the 3M doing heat/AC tests and checking cylinder exhaust temp tests on Auto engines to see if the cylinders are balanced and confirming engine block temps.

*
I've had nearly new cutoff saws sieze from overheating, and realized after seeing them in use on the jobsites, I could see that their safety vests, or coats were getting sucked up against the fan cover, and choking off the cooling air.
They had initially claimed warranty, but after realizing what was causing the failures, they learned to keep the fan covers clear, and the overheat failures stopped.

 

[Big_6]

My tach which has a very fast refresh rate is a Echo pet 304 and is about 5 years old.
You will have to do some searching to see if it's available or been replaced with a later model and the best prices.

jacrawley:
If I were you with a seizing saw I would go with the IR thermometer first probably.

I also think You need to remove the muffler first and take a peek at the piston ASAP before continuing with adjusting and testing.

Gut the epa saw muffler to let it breathe.

Sent from my SM-G900V using Tapatalk

 

[Okie]

I was kinda wondering if temperatures under load are a better tuning indicator than rpms or sound? Agree not very practical for permanent mounting, and would be slower tuning than using a tach or trained ear.

It's been my experience that using the IR temp indicator is not slower. It will start detecting a runway heat condition real fast when the saw is buried in wood and loaded. The temp will head towards 400 F real fast if running lean or the piston is already scrubbing, etc. From experience testing saws a normal temp gets to around 350 slow and max of 375 slow not exceeding 375. On a normal saw you can adjust the H jet lean and bury the saw in wood and the rpm's remain below max spec'ed under load and the saw will start overheating real fast.
This has been my experience and why I always use the IR temp check on my saws before calling them ok to go to the wood lot.
I have a 24 inch downed white pine log handy for doing the IR tests.

I thought of this IR testing sometime back when I had a old 028 stihl seize up in a full bar cut and had been running ok for years. I checked some other saws including Stihls, Homelites, Poulans and some old McCullochs with the IRT (so as to get a average temp of the jug when in a full bar cut) and seen them staying below or around 350F then when I buried the 028 that had seized. (the siezed 028 re-started after a long cool down) I immediately seen it headed for 400F fast and a meltdown using the IRT. I pulled the muffler and all still looked ok and I adjusted the H jet out about 1/2t for a 4 cycling and all ok on the IRT. The tach was at the max unloaded rpms piss reving the saw and it was not 4 cycling. The rpms were less than spec in the cut loaded during overheat, but the engine was running lean. The saw stayed cool when I adjusted H jet for the 4 cycle sound and would immediately start overheating if I went back towards the original carb H jet setting in the full bar cuts.
I went ahead and pulled the carb and installed a kit, checked the fuel lines and filter, did a leak test of the block and she is still doing great today. (something changed to make the saw start running leaner is why I went to the carb kit and inspected other things and the IRT confirmed afterwards and eased my mind that it is not overheating after doing maintenance adjustments)
I use a tach and do the 4 cycle adjustment during preliminary tuning and then confirm the final temp test with the IR thermometer.

 

[Sepia]

Great insights Okie

 

[jacrawley]

I pulled the muffler and it isn't seized but will not rotate past TDC. There were some ferrous nail clippings on top of the piston I can only assume ring fragments. The cylinder wall has a spider Web pattern on it. This saw doesn't seem worth a cylinder replacement to me being a glorified Poulan but what the heck do I know. Thanks for the info everyone you folks are a source of knowledge and inspiration