Stihl 045 AV Rebuild.

[Vintage Engine Repairs]

All good Stihl still sell them via that PN above so I ordered one!
Took the fuel tank apart and gave it a new line filter and gasket and impulse line. I also put new washers on both tank caps, checked the tank vent for function and for a clear fuel passage. That went well. New gasket was old OEM and thus used a little permatex number 3 on it.
That’s the good...

The bad...

I finally got the pull rope on the saw and tested spark today on the spark tester to get an idea of strength. It could hardly bridge the gap! Grrr

I confirmed the gap between magnet and flywheel which was fine, checked the points and capacitor, again both fine and wiring was solid.

Re did the primary and secondary test and secondary gave me some stupid high number. The coil was iffy, I’m done with it now, I’m looking for another.

I have found some aftermarket ones from a shop here in Australia. I hate to use AM parts, but coils can play silly buggers and I fear that I may get a used one and it be problematic. They don’t tend to either work perfectly or die, they can do all sorts and be all strengths depending on condition.

Any thoughts chaps?

 

[Vintage Engine Repairs]

Well I have decided in light of the fact that I can’t get a reasonably priced NOS OEM coil to try the one I have and see. At the very worst, it won’t spark and I’ll invest as necessary. It’s not as if, by it failing, the engine could be damaged like a bearing for example.

cases are together, top end on, ignition all squared away, fuel tank on with new gaskets, lines, filters and o-ring and the recoil cover on.

150 psi compression - feels good.

https://youtube.com/shorts/YJTWw6zYits?feature=share

 

[Mad Professor]

Thanks for the kind words mate damn I’m still so confused by the different types of gauges and measuring devices and nomenclature. I’ll have to re-read your post a few times

That’s a cool little device!! I must admit that I don’t have an issue with the springs (those damn piston c-clips though, I quickly invested in OEM tools for 2 different sizes of clips!!), I just position the outermost end in place and then work my way around and around until I get to the other end and voila.

Hey, do you happen to know if the nozzel check valve in the HS 118A carb is the same in the HS118B carb?

Edit To Update.

i re read your post again, how interesting!
Why doesn’t the mityvac just read in PSI both ways? Crazy.
So when you Vac test saws normally what do you go to? And when you pressure what do you go to?

So technically I should always be doing about 14 inhg on the mityvac for Vac and just the normal 7 psi for pressure?

If you want to add confusion scientists use Atmospheres and Pascals for pressure. Remember ideal gas law? PV = nRT, had to use correct SI units to go with gas constant R, or the teacher got the red pen out.......

1 atm = 101.3 kP = 760mm Hg = 29.9 in Hg = 14.9 psi

This might help with conversions.

Convert millimeter of mercury [0 °C] to pound/square inch.

 

[Mad Professor]

Thanks for the kind words mate damn I’m still so confused by the different types of gauges and measuring devices and nomenclature. I’ll have to re-read your post a few times

That’s a cool little device!! I must admit that I don’t have an issue with the springs (those damn piston c-clips though, I quickly invested in OEM tools for 2 different sizes of clips!!), I just position the outermost end in place and then work my way around and around until I get to the other end and voila.

Hey, do you happen to know if the nozzel check valve in the HS 118A carb is the same in the HS118B carb?

Edit To Update.

i re read your post again, how interesting!
Why doesn’t the mityvac just read in PSI both ways? Crazy.
So when you Vac test saws normally what do you go to? And when you pressure what do you go to?

So technically I should always be doing about 14 inhg on the mityvac for Vac and just the normal 7 psi for pressure?

If you want to add confusion scientists use Atmospheres and Pascals for pressure. Remember ideal gas law? PV = nRT, had to use correct SI units to go with gas constant R, or the teacher got the red pen out.......

1 atm = 101.3 kP = 760mm Hg = 29.9 in Hg = 14.9 psi

This might help with conversions.

Convert millimeter of mercury [0 °C] to pound/square inch.

 

[Mad Professor]

Tom, a thought on the check ball for the valve. What is the diameter? Might be same size as a common steel ball bearing that might fit?

 

[Vintage Engine Repairs]

Tom, a thought on the check ball for the valve. What is the diameter? Might be same size as a common steel ball bearing that might fit?

Thanks mate, I fear it will be too heavy for the small amount of negative pressure to lift the steel ball, I like your thought process though. I was able to source a new OEM valve from the dealer. I was surprised honestly.

 

[Vintage Engine Repairs]

If you want to add confusion scientists use Atmospheres and Pascals for pressure. Remember ideal gas law? PV = nRT, had to use correct SI units to go with gas constant R, or the teacher got the red pen out.......

1 atm = 101.3 kP = 760mm Hg = 29.9 in Hg = 14.9 psi

This might help with conversions.

Convert millimeter of mercury [0 °C] to pound/square inch.

That all went over my head I’m afraid, but I appreciate you taking the time to write it out. Easier to put a red dot at negative 14 And positive 7 haha

 

[PogoInTheWoods]

If you want to add confusion...

Thought I already provided plenty! Gettin' deep, now. LOL

Well I have decided in light of the fact that I can’t get a reasonably priced NOS OEM coil to try the one I have and see. At the very worst, it won’t spark and I’ll invest as necessary. It’s not as if, by it failing, the engine could be damaged like a bearing for example.

cases are together, top end on, ignition all squared away, fuel tank on with new gaskets, lines, filters and o-ring and the recoil cover on.

150 psi compression - feels good.

Very good! FWIW, those Bosch coils were used on several saws and shouldn't be too hard to source. The aftermarket versions seem to have decent reviews and aren't very expensive. The one I bought shoots lightning bolts and metered within Stihl specs, but I seemed to be having a timing issue with the first rebuild before it died and decided to use a good OEM coil I had handy to eliminate a variable. In retrospect, just the rod bearing failing could have been the cause of that. And generally speaking, the only way an older points coil could affect timing would be by it's physical position relative to the magnets. Strength of spark in conjunction with the rest of the ignition components is another story. My guess is the aftermarket coil is fine.

I generally prefer to test a coil secondary directly from the high tension terminal post. And as coils go, there's usually an acceptable tolerance involved that needs to be pretty well exceeded for one not to produce a decent spark..., especially in a points ignition where poor spark is usually associated with either the points or the condenser. But with that reading at around 33,000 ohms too high, you may indeed be exceeding any reasonable expectations for that coil..., or it's an erroneous reading caused by something else in the setup, or perhaps frayed wiring right at the condenser connection entry point of the coil, or the plug wire.

Also, I generally test for spark using a test plug (with an intentionally wider gap) out of the cylinder and directly grounded to the ignition ground plane (not to an anti-vibe isolated area) and use a cordless drill to spin it over -- ( in reverse on the flywheel side or forward on a clutch side). Saves a bunch of rope pulling and is much more convenient during ignition t-shooting mode when swapping components in and out. I'm also just not generally a fan (or have ever needed) an inline or other style tester.

My project is back together just awaiting some fuel and enough courage for me to see if it'll start and stay running this time. Had to re-fashion the kill wire yesterday as my butt splice came apart at the switch not leaving enough length to re-splice. Could have used a couple of those brass terminals mentioned earlier to fix it correctly. Soldered and shrunk for now. The switch retaining nut is also stripped and needs to be replaced. And I needed to replace the oil tank vent with one of the later conventional style vents which have been said to not fit. While a hair long, a newer style seems to be the same outside diameter as the plastic housing version and required installation with a small hammer and drift..., and a touch of JB-Weld for good measure.

As for non-insulated brass terminals, they'll pretty much be crimp connectors which I usually solder anyway.

https://www.google.com/search?q=Bra...XCG80KHeXJAjQQ1QIwF3oECBsQAQ&biw=1366&bih=635

 

[Mad Professor]

Thanks mate, I fear it will be too heavy for the small amount of negative pressure to lift the steel ball, I like your thought process though. I was able to source a new OEM valve from the dealer. I was surprised honestly.

That would be an interesting experiment. There is no spring, that I see holding the ball, it just flops back and forth with pressure or vacuum.

Could use the mityvac to see what/how the mass of the ball effects things.

First you'd need the right size steel bearing and maybe correct size lead shot from a shotgun.......

Not enough time in the day to do that kind of stuff

 

[PogoInTheWoods]

That would be an interesting experiment. There is no spring, that I see holding the ball, it just flops back and forth with pressure or vacuum.

Did a little research to educate myself a bit more on the HS "check valve" issue since I misspoke about it earlier. From a Tillotson source:

​

The Tillotson Nozzle Check Valve has the primary function of protecting the inside of the carburetor in case of a back-fire.​

​

**The check ball seals off the inside of the carburetor preventing damage. While the nozzle length and shape can influence signal and the carburetor's tune, the check ball itself is not a tuning mechanism.**

**If you are experiencing a flooding condition where the high side is leaking fuel at idle, the check ball is not the cause of this problem. Most often, this is due to a leaking seat and or needle valve not sealing.**




​

#19 is technically referred to as a metering nozzle valve (when present). When not present, the space appears to be serviced by #16, #17 and #18 as illustrated in the last two columns. Many early Walbro carbs had such an arrangement (16,17,18) which also utilized a small diaphragm as a check valve to prohibit air from getting back into the fuel passages at idle. I was kinda mixing apples and oranges on that one.

But, hey..., we have a runner! Horrible video, but couldn't help myself and just had throw it up here. A clank here (sprocket?), a rattle there (recoil spring?) (at least I hope that's all it is), but what the hell. It fired right up. Obviously super rich and burning off some assembly lube. I'll baby it along a little before putting on a bar and chain. Also need to see if the new oil tank vent holds before getting too excited and putting an actual tune on it. It may not be finished with me yet, but will get a new recoil badge if it ever figures out I'm actually its friend.

​

 

[Vintage Engine Repairs]

Very interesting pogo! I knew all that info apart from the backfire, this stuff is always good to know, thank you. If that ball leaks it would cause a lean condition in the carb too. I presume the negative pressure within the metering chamber is what draws the ball against its seat. Well done for the rebuild!!! I don’t think I’m too far off mine now

Read point 5 from Zama:


and here is walbro:

 

[Vintage Engine Repairs]

I did the carb today, noticed the seat for the needle was dirty. Some polishing compound on a cotton bud shined it up but under 10x magnification I could see that it was actually pitting!

I have reamed the seats before very successfully, but figured that if it held pressure to 15psi it was good. Tested it and it held. I gave it a bath in the ultrasonic cleaner for 20 mins. Hit it all over with compressed air Installed new needle, lever, welch plugs, gaskets, diaphragms etc and just waiting on the nozzel check valve to arrive

 

[PogoInTheWoods]

Very thorough as usual. Good job.

And if mine running proves nothing else, we now know that 8.5inHg of case vac will provide an adequate pulse to drive an HS118 fuel pump.

 

[Vintage Engine Repairs]

Thanks as always mate that is good news!!

 

[Vintage Engine Repairs]

More stripping, cleaning and rebuilding followed by a first start:

https://youtube.com/shorts/V7BVp4hYzjI?feature=share

 

[PogoInTheWoods]

Excellent work, mate. Congratulations!

Did you ever sort out the coil measurement, or is it actually running with 39,000 Ohms across the secondary?

 

[Vintage Engine Repairs]

Excellent work, mate. Congratulations!

Did you ever sort out the coil measurement, or is it actually running with 39,000 Ohms across the secondary?

Thanks mate, it’s actually around 55k on the secondary now!

I installed the new nozzel ball valve in the carb, when I tested it, it wouldn’t hold, it bled air like the other one... it’s brand new OEM. It makes me wonder if they are designed to fully seal or not. I know the disk version does. I did question if a plastic ball could truly seal. I guess not. Though I do wonder if it could be causing the issues below.

I need to sink it into some wood to clear the crank, however during the preliminary tune you can hear that it’s still got a lean bog off idle.

The idle drilling’s are spotless (I took the welch plug off) and it’s been tuned to Stihl spec. Diaphragms are new as are the gaskets. This was before cleaning the carb, but you can see it’s all clear there.


I even continued to richen the L screw and adjust the idle to compensate and it never improved all the way to the point where the idle screw had no more travel. Still no improvement. I even tried going leaner and no change.

Just now, I remembered, before the rebuild, when I first started it, it had that bog too. I figured it’s old diaphragms or maybe a leaky seal etc, but clearly it’s not that. Carb specific issue maybe?

If I punch the throttle wide open instantly this bog happens, if I pull the trigger slightly slower, it doesn’t happen, it’s smooth. It’s almost like it would benefit from having a larger primary progressive idle drilling (1st progressive drilling behind the butterfly ). It’s like it’s got good fuel at idle, but that transitional change it can’t quite keep up with the demand through the transitional drilling to compensate the drastic opening of the butterfly. Or to enlarge the drilling that lets fuel into that welch plug area!

 

[Bob Hedgecutter]

So the coil- deemed to need splitting an rewound- when fitted up to the saw and allowed to do its job- actually ran the saw perfectly?

 

[Vintage Engine Repairs]

I’ll add this video too for future reference and continuity of the story of this build:

It’s a video of tuning the saw and how richening the L made no improvement.

I’ll take it out for a few cuts later and report back

 

[Vintage Engine Repairs]

Here is the preliminary tune, next I’ll heat soak it and do a final tune as necessary in the wood. I’m going to keep it on the rich side during break in