044 project

[MustangMike]

Exh of 103 would make much more sense. 113 is very low, and not enough blow down.

I would double check that #.

 

[Basher]

I'm done with the squish clearance setting. After dispensing with the BG the clearance I had remaining was ~0.3mm. After hand machining it (P80 grit paper glued to a piston on a stick etc.) its at about 0.6mm (whats that like 24 thou?).

Now I'm degree wheeling it. First time for me on any kind of engine. Took a while to get certain where TDC is...I actually made markings on the ignition side when I did the squish....i.e. where I felt maximum resistance.

View attachment 93578

So here goes, this being *almost* stock. That is, with the jug lowered by 0.4mm by virtue of loosing the BG.

exhaust opens at 113* after TDC
transfers opens at 121* after TDC
inlet at 74*.

Before I go any further I'll just point that don't want the saw to be *too* high revving. The 044 is quoted in the manual as having max engine speed of 14k, so if this engine ends up getting to about 14.2 then I'll be more than happy. I also don't want to touch the transfers - even if I had the confidence - I don't have the equipment.

So what do people e.g. @drf256 reckon? My first thought is to raise the exhaust port - since loosing the BG will have lowered it by 0.4mm - I'd thought by raising by an equivalent amount would be a good move.

I'm also thinking that I saw a @Mastermind post once where he makes the roof of the inlet match with the bottom of piston skirt at TDC - or at least that's what I think he was doing.

Anyway, I'd be interested in yer thoughts.

Best to use a screwed in piston stop to find TDC, screw in the stop, rotate the crank over until the piston contacts the stop, record the degree, then roll the crank all the way back around the opposite direction til the piston contacts the stop again, record the indicated degree. Now TDC is exactly half way between the two readings.

 

[MattG]

Exh of 103 would make much more sense. 113 is very low, and not enough blow down.

I would double check that #.

Yes fair point. It was my attempt. I'll have another go in the next couple days.

Best to use a screwed in piston stop to find TDC, screw in the stop, rotate the crank over until the piston contacts the stop, record the degree, then roll the crank all the way back around the opposite direction til the piston contacts the stop again, record the indicated degree. Now TDC is exactly half way between the two readings.

Yeah, that sounds like the best plan. I'd heard of that before, but I'm not sure if I've got an appropriate bolt whatever to rig that up with right now. Have to have a root about.

So what exhaust degree should I go for? Bearing in mind that I don't wish to touch the transfers, and I'm after torque and revving to not much more than like 14.2-14.5 etc.

 

[MattG]

Can someone confirm whether what I remarked about the inlet roof is correct? That is should I cut that so that it is inline with the bottom of the piston skirt at TDC?

 

[drf256]

113 Ex makes no sense. I’ve never seen one that low stock, even sans gasket.

Basher is correct. You should use a piston stop to find TDC, but there are 2 other ways to do it.

Rotate the saw and observe the piston at the Ex roof, then rotate it again till u see it. Write both down. After 180* rotation, the number should be the same. If it’s 113 the first time and then 96the second, it’s off. Add the 96 and the 113 together to get 209 and then divide by 2 to get 104.5. Then bend your indicator wire to 104.5 andcheck both ways again.

Another way is to just measure duration of the port, as it doesn’t depend on TDC. Find the top of your ex port with the piston, write down the measurement, then rotate the wheel 180* and write that down. That’s the amount of degrees it’s open. You can just use that method of reference, or convert that to opening point by a formula. (360-duration) /2.

This is for Ex and transfers only.

So if your port is open for 160*, 360-160=200. 200/2=100. 100* opening point. If you get opening for 170, 360-170=190. 190/2=95. So 95* opening point.

For intake timing, it the bottom of the piston skirt on the intake floor, not the roof. Just times your reading by 2 for duration, or divide duration by 2 for opening point.

Hope I explained that correctly. Your numbers are off already, so no suggestions can be made yet.

 

[mdavlee]

I use intake floor to set TDC. It's easiest to see and get the same spot. Exhaust is easy to read different with the angle of light.

 

[Basher]

Shine a bright light in the sparkplug hole and rotate the piston downward til you can just see the light break through the exhaust port, back the piston up just a smidge so the light disappears, that is as close as one can get on the exhaust port opening, record the degree reading. I use one of the new LED small diameter flashlights now, they are easy to maneuver and the light is bright white.

 

[Basher]

Can someone confirm whether what I remarked about the inlet roof is correct? That is should I cut that so that it is inline with the bottom of the piston skirt at TDC?

Not sure that matters much, the first few degrees the piston skirt leaves the intake bottom opening will flow the most, dropping the intake opening floor and/or taking some off the bottom of the piston skirt will increase intake duration.

 

[blsnelling]

It sounds as though the OP failed to correctly zero the degree wheel. 113° on the exhaust cannot be correct. One little way of double checking your reading is to check on both sides of TDC. The reading should be the same. If your wheel isn't correctly zeroed, the readings will not be the same.

 

[blsnelling]

Can someone confirm whether what I remarked about the inlet roof is correct? That is should I cut that so that it is inline with the bottom of the piston skirt at TDC?

Leave the roof of the intake port alone. You risk dropping a ring into it of you raise it. I will sometimes raise the roof, but you have to keep this in mind. Also, it's the floor that really matters.

Tip: Port shape can be just as critical, or more so, than port timing.

 

[MattG]

Humble apologies to you guys! I guess my brain was just malfunctioning last night.....I took my time this evening and fortunately I was able to find a Honda civic plug is the same diameter but a lot longer than a diddy saw plug. So I got me a beauty of stop.

So it seems the Exh is at 103* (if you've got any humble pie spare, I'll gladly eat it!). Just to be sure, I timed it in both directions (ATDC and BTDC) and both times I got ~103*.

ATDC:

and BTDC:

So there you go, thanks again people.
(BTW I do really like this technique, with the plug stop, drill chuck and wire etc. it works much better than I'd thought it would. )

 

[MattG]

Hope I explained that correctly. Your numbers are off already, so no suggestions can be made yet.

Yeah, thanks that was great! Like you and Brad said, and I'd kinda guessed earlier today when I was in the workshop, taking readings from either direction is a good sanity check.

You sent me this a while back:

You're gonna have a lot of case pressure with that tiny case. I'd want the transfers physically lower than a standard 12mm hybrid myself.

Like 101/124/76

Bet this saw will rev to the moon.

Now after rechecking etc, I'm reckoning that the numbers for me are currently:

103/122/72

So since my goal is muchos power, but probably not revving much past say 14.2-14.5, and given that I don't want to touch the transfers, what do you now reckon? 101/122/76 or something? Or perhaps slightly less inlet?

Also seeing as the BG delete drops the jug down by 0.4mm, I'm wondering if just by taking that same figure off the exhaust roof will bring me closer to that 101 degree you mentioned earlier.

thanks again

 

[MustangMike]

Just make the intake 76-78 and widen the ports, and I'll bet it runs just great!

 

[blsnelling]

Just make the intake 76-78 and widen the ports, and I'll bet it runs just great!

+1. Flatten the floor of the intake port too.

 

[MattG]

Thanks everyone,

+1. Flatten the floor of the intake port too.

Yeah I'll do something with it! I must admit that the casting at the intake floor looks a bit cr@ppy right now. You can make out a kind of seam quite easily. I'll try to get a piccie next time.

 

[PA Dan]

Install that bushing AFTER you install the seal.

FWIW.....
I ordered the seal press sleeves for an 026 I recently rebuilt for my boss. If you’ve never used the OEM press sleeves, you don’t know what you’re missing.

I agree and they are pretty cheap! The first one I used was building my hybrid and damn was it easy.

 

[MattG]

The first one I used was building my hybrid and damn was it easy.

Makes the ignition side pretty easy to do - even I managed it!

 

[MattG]

(Apologies - this post is just a note-to-self)

This links to MMs ms460 porting numbers
#317

And this is some stuff about inlet ports, which I don't currently understand...
#318

 

[MustangMike]

I will go out on a limb and "generalize", but the #s that work best for one porter may not be the best for another, depending on port size, shape, and the saw.

But, in general, ex high 90s to low 100s, blow down close to 20, intake close to high 70s. That seems to be good starting #s for a lot of the 2 transfer port Stihls.

 

[MattG]

I will go out on a limb and "generalize", but the #s that work best for one porter may not be the best for another, depending on port size, shape, and the saw.

But, in general, ex high 90s to low 100s, blow down close to 20, intake close to high 70s. That seems to be good starting #s for a lot of the 2 transfer port Stihls.

Thanks Mike!