Hot Husky! Overheating I think...

[Vincent Vega]

After rebuilding a Husqvarna 345 with a new 45mm big bore piston and cylinder, it seems to be running a little warmer than usual. I cut a 14" limb and the saw died once the cut was finished. So I reached over to press the decompression valve and got a nasty shock. Seems the saw was running so hot that the plastic body of the decompression valve melted, exposing the metal center which I tried to push.

Prior to this, I tuned the saw with a Fast Tach. I also replaced the plastic carb clamp with a nice metal one. While it was a real PITA to get on, I am very happy with how tight it is vs. the stock one.

So, what's going on here? Too much muffler? Maybe too much cowbell...

 

[Nitroman]

Forget the tach, was the saw four-stroking at WOT out of the cut? Are you sure your mix is good? Did you forget the air conductor?

 

[Boleclimber]

The heat required to melt the decomp button suggest the saw is running lean. Running lean could be from carb settings or an air leak.

 

[Vincent Vega]

Nitroman,

I checked the air conductor, it is firmly in place. The mix is a little old, probably a month or so. I mixed it 50:1 with gas that does have ethanol (yuck). The saw was not four-stroking at WOT out of the cut. Reading through the manual it suggested setting the H screw to 700 RPM lower then the max so the piston and cylinder can wear into each other. To be honest, I've never heard this saw four stroke, which is kinda why I bought the tachometer, to make sure it wasn't running lean!

Boleclimber,

My initial carb settings were one turn out from seated on both the H and L screws. I never found the initial T setting, so I just adjusted it so the chain wasn't moving while the saw was idling. If there's a leak, how might I track it down? Spray carb cleaner near the intake and listen for a change?

 

[Nitroman]

Pull the plug and look at the top of the piston to make sure nothing is burned. The top of the piston should still be nice and shiney from the rebuild.

To check if you have a leak, let the saw idle, use something like Lectromotive or WD-40 that has a plastic straw so you can direct the flow to where you want it. First spray around each junction of fittings from carb to the cylinder. Then point it towards each bearing area. Finally around the base of the cylinder. I don't think you have a leak though.

Before you start it though, you're probably quite lean. Make sure the H screw is out enough that when you try to rev it up it is sloppy and four strokes badly, slowly turn the screw in making sure it continues to four-stroke through the rpm range. It should only clean up once you are in the cut.

 

[Terry Syd]

Does a 345 have the 'air injection' type of centrifugal cleaning for the air intake?

I mention this as it became a serious problem on a saw I was modding. The more I modded, the more air I sucked into the engine - and the less air there was to flow across the cooling fins. I thought I was going to have to cut a clearance band in the top of the piston, but after blocking off the air injection intake and drilling a couple of holes at the back of the air box, the temps dropped right down. - All of the air from the flywheel was now going across the cooling fins.

The mod has another advantage - cleaner air. Over here in Oz the wood is very hard and there are a lot of fines produced. The flywheel intake draws air from the front of the saw. You can see that if you ever cut up a burnt log, the charcoal dust will leave a coating on the front of the flywheel cover and into the openings.

The air injection system works great for larger pieces of sawdust, but the fines don't have enough mass and get sucked into the air box.

If you cut up clean, green softwood, fines aren't a problem and the air injection system works fine. However, here in Oz the air injection system actually increases the amount of fines into the air box.

You can try blocking the air injection system (if the saw has one) and see if it helps with the temps.

 

[KiwiOilBoiler]

The mod has another advantage - cleaner air. Over here in Oz the wood is very hard and there are a lot of fines produced. The flywheel intake draws air from the front of the saw. You can see that if you ever cut up a burnt log, the charcoal dust will leave a coating on the front of the flywheel cover and into the openings.



.

Terry, my saw mentor suggested I perform the same mod to my 288, saying that it would keep the filter much cleaner.288's have a 'window' where air-injection ducting looks like it could go, but is not installed. I'm just too sissy to drill holes in my hi-top, but I see his and your point.

Adam

 

[Terry Syd]

It wasn't so much as a 'leap of faith' for me as it was survival. I had increased the displacement 9% and the cutting speed by 33%. So now I had the engine producing a lot more heat. Of course, what I missed was that to create that extra heat I was pulling air from the flywheel (via the air injection) - air that should have been going to keep the engine cool.

I was producing more heat at the same time I was reducing cooling - DUH!

After blocking off the air injection system with some liquid rubber, I noticed that the air cleaner wasn't getting as dirty as it had. That's curious I thought, the air injection system is blocked off?? I figured it would get dirtier faster.

The light came on when I cut up a blackened stump. The carbon tracings on the saw showed where the air flow came from. I was sucking fines right off the bar.

EDIT: Here's something else to consider - a two-stroke makes less power when it is hot.

An air-cooled two-stroke can make up to 20% difference in power between a 'flash' cold reading on a dyno and a hot continuous run on the dyno. Thankfully for chainsaw users the difference is less with a fan-cooled engine (and water-cooled is a step above that).

However, if you are removing the fan air from the jug, you are removing some of that advantage.

Here's a story I like to tell about using that HEAT concept to win a race. I used to be a desert racer in California back in the '70s. One of the guys in the club bought one of the new Huskys (400 as I remember) that had more power than the old Husky 360s. He was bragging about his new purchase, so I conspired with one of the blokes that had a 360.

We arranged a drag race down at the dry lake bed at Lucerne to sort out the difference. As the three of us headed down to the lake bed for the race, the bloke with the 360 had his choke on and the engine kept missing (and keeping the engine cooler).

When we got to the lake bed, the 360 bloke pretended he had a bad sparkplug (because of all the coughing a sputtering of the engine). So the smug bastard and I had a couple of drag races out on the lake bed while the 360 bloke changed the spark plug (and I heated up smug bastard's engine).

With the Husky's lined up, the race was on and the 360 bloke won by more than two bike lengths. Smug Bastard was completely freaked out, he had just laid down some coin for a dog.

Later that night sitting around the campfire we told him what we did and had a good laugh.

 

[Nitroman]

If I lived in the Lower 48 where it gets truly hot, I would have the jugs of my saws anodized black to remove heat. As it is...this is something I don't have to worry about.

Good story.

 

[Vincent Vega]

Nitroman,

I pulled the spark plug and much to my surprise, the top of the piston was not shiny. It had a medium gray film coating it. The H screw had also been set to a 1/2 turn out.

I ended up setting the L screw to 2 turns out and the H to 1.5. I think these settings made it "four stroke" at idle. No matter how I played with the H screw, I couldn't seem to get it to four stroke through the RPM range. If I backed it out too much, it would burble and die and if I turned it in too much the four stroking sound disappeared.

Then taking a can of WD40 I sprayed around the carb, the carb clamp to the jug, the base gasket, and down where the bearings are. When I sprayed WD40 on the top part of the carb clamp the saw would die. I ended up taking a video of it to help show what's going on. You can also hear the saw four stroking??? at idle. Just for kicks, I checked with the Fast Tach and it was idling around 3,000 RPM and was around 9,500 RPM at WOT.

[video=youtube_share;lMv1MlpJN-0]http://youtu.be/lMv1MlpJN-0[/video]

Terry Syd,

I'm not sure if the 345 has Air Injection centrifugal cleaning. After looking at a PDF online that describes the set up, it looks pretty similar to what I have.

View attachment 312190

View attachment 312191

My saw doesn't have any directional fins above the flywheel ones like the diagram indicates.

And that was a pretty clever trick you pulled. I got a good laugh from reading about it!

 

[nmurph]

I hate to be Mr. Obvious, but you have an air leak around the clamp.

 

[w8ye]

The air injector is a bolt on plastic device

 

[Boleclimber]

Adjusting the carb is nearly impossible until the air leak is fixed. Is that a bolt style clamp like the ones found on a 372 or automotive crush type clamp?

 

[o8f150]

Nitroman,

I pulled the spark plug and much to my surprise, the top of the piston was not shiny. It had a medium gray film coating it. The H screw had also been set to a 1/2 turn out.

I ended up setting the L screw to 2 turns out and the H to 1.5. I think these settings made it "four stroke" at idle. No matter how I played with the H screw, I couldn't seem to get it to four stroke through the RPM range. If I backed it out too much, it would burble and die and if I turned it in too much the four stroking sound disappeared.

Then taking a can of WD40 I sprayed around the carb, the carb clamp to the jug, the base gasket, and down where the bearings are. When I sprayed WD40 on the top part of the carb clamp the saw would die. I ended up taking a video of it to help show what's going on. You can also hear the saw four stroking??? at idle. Just for kicks, I checked with the Fast Tach and it was idling around 3,000 RPM and was around 9,500 RPM at WOT.

[video=youtube_share;lMv1MlpJN-0]http://youtu.be/lMv1MlpJN-0[/video]

Terry Syd,

I'm not sure if the 345 has Air Injection centrifugal cleaning. After looking at a PDF online that describes the set up, it looks pretty similar to what I have.

View attachment 312190

View attachment 312191

My saw doesn't have any directional fins above the flywheel ones like the diagram indicates.

And that was a pretty clever trick you pulled. I got a good laugh from reading about it!

sounds leaner then hell to me

 

[Vincent Vega]

Adjusting the carb is nearly impossible until the air leak is fixed. Is that a bolt style clamp like the ones found on a 372 or automotive crush type clamp?

It is the crush style clamp.

View attachment 312196

Bad picture, but here it is on the saw:

View attachment 312197

In the stock image, there is a washer holding the clamp together. But when I clamped it on the saw, I did not use the washer but slid the tongue into the groove of the clamp. It was really, REALLY, tough to get the clamp to do that, so maybe I wasn't supposed to.

Perhaps the partition wall intake is not sealing like it should because of an overtightened clamp... And the result is the air leak nmurph has pointed out.

 

[Boleclimber]

Read through the thread below. You likely want to adapt a 372 clamp to fit.


http://www.arboristsite.com/chainsaw/242891.htm

 

[Nitroman]

First: the gray of the piston tells me it got hot. But you should be okay.

Second: You are four-stroking all the way.

Lastly: like NMurph stated, you have a bad leak. Get the leak fixed first. Sometimes when a clamp is too tight, it'll smush the rubber a little too much right under it forming a passage.

 

[mountainlake]

What's going on here, you had the saw set at 1/2 turn out and almost burnt it up, now you have it set 1-1/2 turns out and it's pig rich. Try setting it at 7/8 to 1 turn out where it should be and do another vid. You might have a air leak but spraying WD40 on top of the clamp might get right into the carb intake. Steve

 

[mountainlake]

Also when setting a carb it's only 1/8 of a turn one way or another.. What RPM was it turning when you had it set a 1/2 turn ? Don't be thinking really high rpm will cut faster than a properly adjusted carb, it will just bog easy. Steve

 

[SawTroll]

Does a 345 have the 'air injection' type of centrifugal cleaning for the air intake?

It does have it.