066 Top End # ..... uh, whatever

[mtngun]

Looks like the Meteor is still backordered, so I might as well give the BB kit a whirl while I'm waiting for the Meteor

Besides the aggressive port timing, there's another concern with the BB kit. I didn't mention it before because I was waiting to see what Grande Dog had to say. Well, he didn't say much, so I'm on my own with this kit.

The very top of the bore seems to be missing plating and seems to be a little rough -- hard to say for sure because of the limited visibility. Lacking a bore scope/camera, all a guy can see with the naked eye is a dark ring. On average, this mysterious dark ring extends 1/8" into the bore, but in one place it creeps down nearly 0.150". The top ring will probably go part way into the mysterious dark ring at TDC.

Because of the mysterious dark ring, a pop-up piston is definitely out of the question. The standard piston MAY be OK -- my thinking is that the bottom ring will always be on good bore and provide a good seal, even if the top ring has difficulty.

Other than crappy area at the top of the bore, fit and finish on this kit is 1st rate. If you buy one of these, just be sure to inspect the very top of the bore before you install the kit.

I'm planting trees today, but should be able to bolt the kit on tomorrow night.

 

[wigglesworth]

Are you sure it's not plated there? It could just be where the hone stopped during final machining.

 

[mtngun]

Are you sure it's not plated there? It could just be where the hone stopped during final machining.

No, I'm not sure about the plating. No way to examine it closely -- without sawing the cylinder in half. All I know is that it looks different and feels different. It has texture, it's not smooth and shiny like the rest of the bore.

 

[wigglesworth]

No, I'm not sure about the plating. No way to examine it closely -- without sawing the cylinder in half. All I know is that it looks different and feels different. It has texture, it's not smooth and shiny like the rest of the bore.

Take a piece of fine, like 400 grit, and go around the "dark ring" and see if it doesn't hone up. Are you going with less than .100 to the top ring? If you ad the .020 for the squish, you have .120 to play with before running out of good bore. Id hit it with some sand paper first and then have a look.

 

[parrisw]

No, I'm not sure about the plating. No way to examine it closely -- without sawing the cylinder in half. All I know is that it looks different and feels different. It has texture, it's not smooth and shiny like the rest of the bore.

Use a small mechanic's telescoping mirror to get inside the combustion chamber a little and you can see how far the plating goes up.

 

[mtngun]

Got the BB kit installed. No pop-up, no porting, no grinding on the piston windows, no nothing. Just set squish.. Several reasons, one of which is that, if this kit doesn't work satisfactorilyl, I don't want it blamed on something I did, since there ARE issues with this kit.

I measured 0.035" - 0.036" squish with the supplied gasket.

However, I was measuring about 0.05" - 0.100" into the solder, assuming there was a machined squish band at the edge of the chamber like most jugs. Bad assumption. This dome tapers all the way to the edge, so I should have measured at the very edge of the solder. Had I done so, squish probably would have show 0.030" - 0.032".

But, I didn't figure that out till later. Meanwhile, I shaved 0.015" off the base and tried again, expecting to find 0.020" squish. Instead, I was seeing inconsistent squish numbers. That's when I figured out the dome was tapered all the way to the edge. Squish at the edge was 0.015" - 0.016". :censored:

I added a 0.005" paper gasket and came up with 0.023" squish at the very edge. Close enough.

Both rings gapped 0.011".

By the way, while I had the saw apart, I measured the con rod length as best I could, for use with the computer port timing calculations. It seems to be at least 70mm long. Previously, I'd been using 68mm long, because that's what another AS member used, but from now on I'll use 70mm until someone steps forward with the official Stihl spec.

Port timing as measured with a degree wheel:

169 degrees exhaust duration
178 degrees intake duration (is that some kind of record ? )
32.5 degrees blowdown

Mr. Murphy paid a visit and left this where the oiler pawl was supposed to be. :censored: I'll have to order a replacement, meanwhile, no sawing.

Fired it up, did some rough carb tuning, and let it idle for about 15 minutes. Tomorrow morning I'll check the cold compression. Not much more to be done until the oiler is repaired.

 

[mtngun]

Use a small mechanic's telescoping mirror to get inside the combustion chamber a little and you can see how far the plating goes up.

I'll have to pick one of those mirrors.

In the meantime, I sawed a similar NWP jug in half. Like the BB jug, it also had a dark, textured ring at the very top of the bore. I think this pic shows that the dark textured ring is definitely missing plating. There may be some other issues, too. This particular spot we are looking at would have been swept by the top ring, so you can imagine all kinds of issues with that.

I would suggest to anyone who buys an aftermarket jug, to inspect the top of the bore very carefully. They will run with this kind of defect, but the compression may be below par, or the ring life and bore life may be short.

 

[mtngun]

Tested compression this morning. 150 psi.

That's very, very good considering it only has 10 - 15 minutes run time and the altitude is 4600 feet. 150 psi here is equivalent to 175 psi at sea level.

Ordered a used oiler gear thingy, won't be able to do any cutting speed tests until it arrives.

Grande Dog deserves a big pat on the back for shrinking the combustion chamber on the 066BB. Now, if he could get the bore issues under control, and knock the port durations down to 150 - 160 degrees .........

 

[Tohya]

Hello,

I'd ask some questions, but I've found the answers all ready.


Just to add to this thread. Here are a few images of the 066BB kit I have.

 

[mtngun]

Thanks for the pics, Tohya. Looks like at least 4/32", or 0.125", of bad bore at the top. In theory, it shouldn't hurt anything, as long as it doesn't extend down to the rings.

In fairness to Baileys, some OEM jugs have the same problem -- but I'd say the NWP manufacturer definitely needs to pay more attention to the top of the bore.

Tohya's BB port map.

In other news, the oiler worm gear thingy showed up and I was able to put a tank of gas through the BB this evening, bucking firewood with a 24" bar. It's tuned pig rich, so it wasn't screaming through the wood, but it did OK.

Afterwards, compression hot was 115 psi. Pulled the muffler cover and the engine looks fine. I'll try to do a timed cut tomorrow.

 

[Tohya]

The unplated part of the bore is very consistent at 4/32", so the rings won't reach it.

The waviness to the port map, is from the large and irregular chamfer on the transfer and exhaust ports. I'd post a pic but my cell phone doesn't want to take a clear picture of them.

 

[mtngun]

Here is my BB's port map. Critical numbers are nearly identical to yours.

I rechecked compression this morning, expecting the cold compression to be 10 - 20 psi more than last night's hot compression. No, only 90 pounds, even though there is plenty of resistance on the starter cord. The gage was giving believable numbers just a few days ago, but I don't trust it now. Speed test to follow when time allows.

 

[mtngun]

Speed test, milling a 12.5" pine cant with 36" bar and 7pin rim. :chainsawguy:

Saw was tuned to 13,000 WOT with the 36" B&C at the beginning of the test. Normally I detune my milling saw down to 12,000 - 12,500, but this top end seemed to want to run a little faster.

Two passes were made with Woodland Pro lo-profile milling chain, then two passes were made with WP 3/8 milling chain.

lo-pro x 0.050" 1st pass 0.79 in/sec, 2nd pass 0.83 in/sec, average 0.81 in/sec. The saw seemed happiest pulling 10,000 - 10,400 RPM.

3/8 x 0.063" 1st pass 0.56 in/sec, 2nd pass 0.67 in/sec, average 0.62 in/sec. Saw seemed happiest pulling 9100 - 10,000 RPM.

Here is a summary of all the milling speed tests I have done so far, ordered fastest to slowest:

Lo-pro
0.81 in/sec new "as-is" BB
0.76 in/sec wood ported 2008 vintage BB with chattered bore
0.73 in sec wood ported OEM with damaged bore
0.69 in/sec "as-is" 2008 vintage BB with chattered bore

3/8" x 0.063"
0.64 in/sec "as-is" 2008 vintage BB with chattered bore
0.62 in/sec new "as-is" BB
0.53 in/sec wood ported OEM with damaged bore

The new BB did good today, with the lo-pro chain. The lo-pro seems well suited to saws with peaky power bands, because it lets the saw rev a little faster, where it makes more power.

I'll update when I get a new compression tester. That may be a few weeks yet.

 

[woodgrenade]

Did you try the comp tester on your other saws to see if they are giving low numbers too? Have you been using a new base gasket with every cylinder swap?(Just curious)

And oh yeah......, awesome posts I would rep you again if I could.

 

[mtngun]

Did you try the comp tester on your other saws to see if they are giving low numbers too? Have you been using a new base gasket with every cylinder swap?(Just curious)

And oh yeah......, awesome posts I would rep you again if I could.

My tester is giving suspiciously low numbers on my other saw, too. The numbers are low, yet the saws pass a drop test and are darned tough to pull-start without using the decomp valve. The suspicious readings just started a few days ago.

This top end uses the base gasket supplied in the kit, plus I added a thin paper gasket, smeared with hylomar, to set the squish. I have no reason to believe that it has an air leak -- it was running pig rich until I tuned it for this test, the piston looks like new, it idles fine, etc..

 

[woodgrenade]

Everything looks great, I really liked seeing all of your #'s and ways of gaining compression. Hopefully the quest is over with.

 

[Brmorgan]

Overkill, milling a 12.5" pine cant with 36" bar and 7pin rim. :chainsawguy:

I fixed it for you.

Just kiddin'. Been there plenty of times with the 33" bar myself.

 

[mtngun]

An update......since the BB seems to run well enough, I'm going to leave it in, and save the used OEM jug for some future project saw. However, the Meteor piston showed up today, so I might as well post a little review on it.

The Meteor arrived with the wrist pin rattling around in the box with the piston, creating a scuffed spot on the piston. It won't effect performance, still......... Meteor needs to do a better job of packaging the wrist pin.

Otherwise, fit and finish is great. Critical dimensions are practically the same as OEM -- top land is 0.140" (making a 0.040" pop-up possible ), pin center to deck is 23 mm, and overall height is a hair over 43 mm. The wrist pin fit its bore perfectly.

Arrow points to scuff mark.

 

[Brmorgan]

An update......since the BB seems to run well enough, I'm going to leave it in, and save the used OEM jug for some future project saw. However, the Meteor piston showed up today, so I might as well post a little review on it.

The Meteor arrived with the wrist pin rattling around in the box with the piston, creating a scuffed spot on the piston. It won't effect performance, still......... Meteor needs to do a better job of packaging the wrist pin.

Otherwise, fit and finish is great. Critical dimensions are practically the same as OEM -- top land is 0.140" (making a 0.040" pop-up possible ), pin center to deck is 23 mm, and overall height is a hair over 43 mm. The wrist pin fit its bore perfectly.

Arrow points to scuff mark.

Yer pic isn't showing up for some reason.

I had the exact same problem with my Meteor's packaging. They could use a little stuffing or something.

 

[mtngun]

Yer pic isn't showing up for some reason.

Sorry, I think it's fixed.