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bmp01

Tuned 395xp - ignition timing

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Simple question, what ignition timing advance would you run on a tuned 395xp ? 

 

Except its not that simple is it, because you need to know what tuning has been done...ok, well briefly, 

Muffler mod, gutted internals with twin outlets

Transfer ports opened out at the entry.

Inlet port cleaned up to remove flash line.

Exhaust port raised slightly.

Squish band machined 0.45mm

Cylinder base machined 0.8mm

Base gasket 0.25 (std is 0.5ish)

Squish is 0.5mm after all this, compression pressure - dunno, cant pull it over without deploying the decomp valve. With decomp open I get 100psi.

 

Ran pretty strong with standard ignition timing but started to behave weirdly after a good long run (its a milling saw), with the idle speed unstable. Air leak. Replaced the crank seals. Inspecting the old ones - the flywheel side had been leaking, sawdust between the dirt lip and the sealing lip, sawdust inside the seal and on the face of the b/e bearing. Clutch side seal in contrast was nice and clean. I'm happy to have got away with that (air leak)... not so happy about stripping the key out of the flywheel though. 100% sure flywheel was seated and torqued up properly. My mistake - I think - was not degreasing the crankshaft taper...

New flywheel is 200 quid so that's not happening.

 

Cutting to the chase,  timing light says I have a tad under 20 degrees of advance. Given the high compression of engine it might be I don't need huge advance but everything I've found thus far suggests 25 - 30 degrees BTDC. 

 

Comments? 

 

Thanks,  bmp01

 

Edited by bmp01
Corrections 2

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1 minute ago, bmp01 said:

Simple question, what ignition timing advance would you run on a tuned 395xp ? 

 

Except its not that simple is it, because you need to know what tuning has been done...ok, well briefly, 

Muffler mod, gutted internals with twin let outlets.

Transfer ports opened out at the entry.

Inlet port cleaned up to remove flash line.

Exhaust port raised slightly.

Squish band machined 0.45mm

Cylinder base machined 0.8mm

Base gasket 0.25 (std is 0.5ish)

Squish is 0.5mm after all this, compression pressure - dunno, cant pull it over without deloying the decomp valve. With decomp open I get 100psi.

 

Ran pretty strong with standard ignition timing but started to behave weirdly after a good long run (its a milling saw) with the idle speed unstable. Airleak. Replaced the crank seals. Inspecting the old ones - the flywheel side had been leaking, sawdust between the dirt lip and the sealing lip, sawdust inside the seal and on the face of the b/e bearing. Clutch side sealin contrast was nice and clean. I'm happy to have got away with that (airleak)... not so happy about stripping the key out of the flywheel though. 100% sure flywheel was seated and torqued up properly. My mistake - I think - was not degreasing the crankshaft taper...

New flywheel is 200 quid so that's not happening.

 

Cutting to the chase,  timing light says I have a tad under 20 degrees of advance. Given the high compression of engine it might be I don't need huge advance but everything I've found thus far suggests 25 - 30 degrees BTDC. 

 

Comments? 

 

 

Nothing other than be interested in result . I have a 395 from Walker saw Shop . Its got a twin port muffler but not sure if anything else has been done .

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Again speak to Spud as he sorted me out with a flywheel for mine when it stripped the keyway.

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Thanks chaps, I'm sure Spud will have some thoughts on this and hope he will comment on the thread when he gets a chance, no need to drag him away from his paid work just yet.

 

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I assume the flywheel is the same sort of thing as other husqvarna saws with a little bump cast into it instead of a proper key? You might be able to put a steel key in the crankshaft and file a slot into the flywheel for it to fit into. 

 

Afaik the taper should hold the flywheel rather than relying on the key to be under torque, so you may be able to line the keyless flywheel up and tighten it down properly. I did this with a huztl 372 I built and tore the key out of. I did eventually replace the flywheel for peace of mind, but it ran ok. I just used a marker pen to mark the relative positions of the key and key way before fitting.

 

As for changing the timing. No idea, but pushing a milling saw to it's limit might expedite it's demise.

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At what RPM did you take the reading? Did you test it at WOT? Saws are usually in the high 20's or 30* range at WOT. Most all modern saws will advance the ignition.

 

 

Edited by wyk

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1 hour ago, Toad said:

I assume the flywheel is the same sort of thing as other husqvarna saws with a little bump cast into it instead of a proper key? You might be able to put a steel key in the crankshaft and file a slot into the flywheel for it to fit into. 

 

Afaik the taper should hold the flywheel rather than relying on the key to be under torque, so you may be able to line the keyless flywheel up and tighten it down properly. I did this with a huztl 372 I built and tore the key out of. I did eventually replace the flywheel for peace of mind, but it ran ok. I just used a marker pen to mark the relative positions of the key and key way before fitting.

 

As for changing the timing. No idea, but pushing a milling saw to it's limit might expedite it's demise.

Yes, cast in key. It left a witness in the flywheel taper after it departed. I used a ball nose cutter in a Dremel to very carefully add a round groove into the flywheel.  A 3mm pin is then used as the alignment feature. Accuracy was in the order of 0.25mm (magnifier deployed etc) but even then it's at a very small radius so that could be several degrees. I've also lapped the flywheel onto the shaft for maximum torque capability (spoken about quite a lot on the American site's and copied from 2 stroke racing bike engines), should be better than the original engagement. 

 

Not blowing the engine up with too much advance is at the forefront of my thinking but equally running retarded from optimum will leave a lot of heat in the exhaust gases (and presumably piston, cylinder )...

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58 minutes ago, wyk said:

At what RPM did you take the reading? Did you test it at WOT? Saws are usually in the high 20's or 30* range at WOT. Most all modern saws will advance the ignition.

 

 

With the coil I have on the saw it's fixed timing at idle and above. No idea if it's the original coil, saw was secondhand when i got it, I should go and check part number on coil though - I'll do that...

Testing was done the same as the video,  find tdc, mark flywheel and casing.  I then marked 10, 20, 30 degrees of advance on the flywheel so I could read advance directly. Removing flywheel cover while engine was running was surprising easy,  but you need to be precise and deliberate with removal. ...

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Mmmm, good luck getting anyone in the UK answering this one with any knowledge or experience as it is a bit specialized and probably beyond most but having set the timing on a 066 red eye fitted with a much later coil and sorting a few dodgy MS150 flywheels in my time...............

I would take another 395 unmodified, put a spacer between the piston and the squish band (through the plug hole makes sense), turn the flywheel in one specific direction and work out where a chosen flywheel fin lines up with a fixed point - perhaps part of the coil.

If you then compare this to your machine, you can see how far from standard you are and how much advance you have as 1mm on the edge of the flywheel (of this size) equates to one degree.

I usually run 4-6 degrees advance on from standard on my standard build - much easier if the key is in place but other than sodding around with strobe timing lights as I did on my red eye 066 (circa 22-23 degrees at idle), this method is much easier and is reliable.

Most modern saws do have some advance and retard curve as we all know:001_rolleyes:....two strokes like low advance at idle, rapidly rising to 22-27 at mid revs then rapidly falling off when flat out otherwise, big bangs which is nothing like four strokes which advance throughout their rev range.

For those who haven't a clue what we are talking about.....go back to X factor, dancing on ice or some other inane TV prog!!!

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