What's on your bench today?

[Khriss]

30 minutes ago, bmp01 said:

 

 

As an aside, ever heard of ring groove porting? Several small drillings to get combustion gas to the back of ring. Drillings in top edge of ring groove only.

 

... No.... And thats Witchcraft an yr probly gonna get burnt at the  stake if you do that  😯  K

[bmp01]

18 minutes ago, Khriss said:

... No.... And thats Witchcraft an yr probly gonna get burnt at the  stake if you do that  😯  K

Damn, thats a bit of a bugger then.....

[Khriss]

15 minutes ago, bmp01 said:

Damn, thats a bit of a bugger then.....

....... I'll get me cloak 😉  k

[spudulike]

It is an easy one, there is something that is stopping the saw reaching peak revs - Circa 14700+ on this saw. All you have to do is find it! 

Electrical - you may be getting something stopping the coil doing what it should, is it a blue limited coil....probably not and none of the limited blue coils limit to 12Krpm. Perhaps there is arcing on the plug or cap or the kill wire/HT lead is touching earth or the coil is shot. In my experience, these arcing/shorting issues don't cause rev limiting issues,they stop the engine. A limited coil can blow the high speed section so an engine won't rev out, seen that on a 361 and a blower so it does happen but isn't common. You could try many of the coils off the 3 series saws just observing some may be limited so will send a tach all over the place once it hits the limiter. Check the HT lead with a multimeter and check connections at both ends, check the kill wire or just disconnect it. Check the coil gap.

Fuel - how is the saw running? Wet, oily, smokey black plug or is it lacking power, bogging, lacking power. If the carb is throwing in too much fuel, you will be getting a heavy fuel residue. It is possible you are getting far too much fuel or far too little. I would pressure check the fuel line, check the tank breather and also the HOLE that goes in to the carb elbow as I have seen two with the through hole not present! Check the gauze strainer - take it out and use a magnifying glass, get carb cleaner down the H and low screw, check the pump diaphragm, especially the pump flaps and pressure check the carb.

Mechanics - Check out the piston for the things BMP has mentioned, chack the compression, 150 is getting low on these saws, 170 is decent. Check the first hard pull. With the base gasket deleted, you should be 80-100psi - if this is much lower and you don't get up to almost max reading in 3-4 pulls, the engine isn't in good shape.

Check the bore and plating for wear and discoloration. Check the inlet manifold, especially the impulse nipple (Yes, I did say NIPPLE)....it often splits along the top or can get distorted if not fitted properly. Is the short impulse line fitted between the inlet clamp and the carb connector fitted correctly - just had this problem!! make sure the inlet manifold perforated inlet support sleeve is fitted.

Make sure the muffler isn't blocked - had one plugged with mud once!!!

I can't think of much more - I have just spent 4 hours on a 200 I had rebuilt that just wouldn't start. I had replaced the HT cable and was getting a big fat blue spark jumping 7mm so it was never going to be an HT problem was it......cock yes it was, after stripping it doing a full leak test, swapping carbs, coils, flywheels etc etc, I swapped the HT lead and bingo....the HT lead being screwed on had forced the copper strands deep in to the sheath making a bad connection - great spark in air, none under the 200psi compression the saw had!!

If you check all possible issues, the issue left, however improbable, is the culprit!

 

 

[openspaceman]

2 hours ago, spudulike said:

Make sure the muffler isn't blocked - had one plugged with mud once!!!

I test for spark then compression then this. Not something I've come across with saws but the Stihl BT45 drills were forever clogging their mufflers and it was the spark arrestor that clogged.

[billpierce]

4 hours ago, spudulike said:

It is an easy one, there is something that is stopping the saw reaching peak revs - Circa 14700+ on this saw. All you have to do is find it! 

Electrical - you may be getting something stopping the coil doing what it should, is it a blue limited coil....probably not and none of the limited blue coils limit to 12Krpm. Perhaps there is arcing on the plug or cap or the kill wire/HT lead is touching earth or the coil is shot. In my experience, these arcing/shorting issues don't cause rev limiting issues,they stop the engine. A limited coil can blow the high speed section so an engine won't rev out, seen that on a 361 and a blower so it does happen but isn't common. You could try many of the coils off the 3 series saws just observing some may be limited so will send a tach all over the place once it hits the limiter. Check the HT lead with a multimeter and check connections at both ends, check the kill wire or just disconnect it. Check the coil gap.

Fuel - how is the saw running? Wet, oily, smokey black plug or is it lacking power, bogging, lacking power. If the carb is throwing in too much fuel, you will be getting a heavy fuel residue. It is possible you are getting far too much fuel or far too little. I would pressure check the fuel line, check the tank breather and also the HOLE that goes in to the carb elbow as I have seen two with the through hole not present! Check the gauze strainer - take it out and use a magnifying glass, get carb cleaner down the H and low screw, check the pump diaphragm, especially the pump flaps and pressure check the carb.

Mechanics - Check out the piston for the things BMP has mentioned, chack the compression, 150 is getting low on these saws, 170 is decent. Check the first hard pull. With the base gasket deleted, you should be 80-100psi - if this is much lower and you don't get up to almost max reading in 3-4 pulls, the engine isn't in good shape.

Check the bore and plating for wear and discoloration. Check the inlet manifold, especially the impulse nipple (Yes, I did say NIPPLE)....it often splits along the top or can get distorted if not fitted properly. Is the short impulse line fitted between the inlet clamp and the carb connector fitted correctly - just had this problem!! make sure the inlet manifold perforated inlet support sleeve is fitted.

Make sure the muffler isn't blocked - had one plugged with mud once!!!

I can't think of much more - I have just spent 4 hours on a 200 I had rebuilt that just wouldn't start. I had replaced the HT cable and was getting a big fat blue spark jumping 7mm so it was never going to be an HT problem was it......cock yes it was, after stripping it doing a full leak test, swapping carbs, coils, flywheels etc etc, I swapped the HT lead and bingo....the HT lead being screwed on had forced the copper strands deep in to the sheath making a bad connection - great spark in air, none under the 200psi compression the saw had!!

If you check all possible issues, the issue left, however improbable, is the culprit!

 

 

Thankyou for the thorough reply. Have done an awful lot of those things, but still more to do. Will let you know how I get on

[billpierce]

On 05/12/2020 at 19:48, spudulike said:

The Gunson gauge is one of the more reliable ones, I did keep blowing the schrader valves on modified saws so fitted a Presta one and it has lasted well. 

A decent 346 should have 170psi.

What was the end gap like? 7 thou is good, below 20 is OK, anything over and it is looking a bit iffy. 

Sometimes you have to tear it all down again and then build it up again to get to where you need to be.

Are there signs of it being over-fueled  such as a wet oily residue, black plug etc. 

The only time I have come across this sort of issue is with saws with excessive top end wear, the last one was an 020T that was doing exactly the same thing, couldn't get the revs above 12k even with the H screw turned in!

It is possible the HT cap is leaking down making the high revs miss or the carb having a leaking check valve or the coil being like your 361 one but that was a limited one.....weird one but my diagnosis head still comes back to engine wear.

Stick a new piston in it😉

Sorry seem to be missing posts dont know why. 

 

Have tried a 357 coil and swapped the carbs and still the same so piston swop next!

[billpierce]

On 06/12/2020 at 08:49, bmp01 said:

Think you've done enough engines by to know what to look for, residue on piston ie combustion gases passing the rings never a good sign.  If the piston is unworn ie. still showing turning marks on the skirt and rings are unworn  maybe the ring grooves are choked up with crud ? Piston ring does some sealing on its own but it also needs the combustion gas to get on top AND behind the ring to force it onto the cylinder wall. Obviously if the ring groove is too tight (piston made wrong or clagged up) - then that doesn't happen.... result is blowby past the ring. Swaping in new piston is obvious solution.

 

Is the cylinder bore shiny ? Might be worth a gentle deglaze ?

 

As an aside, ever heard of ring groove porting? Several small drillings to get combustion gas to the back of ring. Drillings in top edge of ring groove only.

 

Thanks bmp! Going to swop pistons out

[Khriss]

'Whats On Your Wilko Workmate Today "

 

Annoyed at the cockrings coming off my high lifts, so knocked up a simple press using 50mm channel and hydraulic ram kit. 

 

 

[Khriss]

10 ton crush it on nicely

 

No tree company should be without one. Good for hammer shafts too.  ☺️

 

( chuck em in a bucket of water after to swell up )  K