Requesting help porting 066 BB Woodlands Kit

[Martinm210]

So I'll start off by saying, I've never ported a cylinder before and not sure I need to on this one. I have rebuilt a few dirt bike motors in the past, but I usually had someone else do the port work. But in spirit of learning, I decided to try and make my first port map and see if I can figure out the timing of the ports. I also have a second 066 case with stock jug (scored piston) that I decided to use as a comparison to stock.

The kit is one of the overseas cheap kits and is obviously not to the same level of quality as the stock piston and cylinder, but regardless, it's what I had money for so I bought one and plan to run it. No plans to use this saw professionally, just for my yearly firewood cutting needs. I also have a stock MS290 that I've been using for years and have as a backup, so I'm really just having fun with this little project.

Anyhow, here is my side by side comparison of the jugs and pistons:
Besides the obvious 54mm stock vs 56mm Woodlands BB the Woodlands piston is also 2mm shorter and has about .3mm less piston offset and porting is slightly different. Overall the exterior of the jug looks good, just the casting roughness of the ports and dome that are poor. That's where the porting or if nothing else port polishing comes in though..

The quality differences are apparent, stock piston is superior in strength and design. With that aside I wanted to look at the skirt of the pistons and compare the port sizes. It appears the stock piston has slightly larger openings in the sides for tansfer. Perhaps I can simply do some light cleanup of the casting edges in the openings (don't want to take any strength away).

And here is my first attempt at port mapping. I did both cyclinders and cut the split in the same location for comparison purposes. The obvious thing to me is the stock cylinder ports are generally more rounded and the transfer ports are sloped to push the gases. I'm assuming this sloping of the ports is intended to push the gases towards the intake side of the cylinder and wash the exhaust out better, not sure though.

Port Maps

Not sure, but it seems like the transfer ports may be weak on the BB cylinder.?

Port Timing Calculator
Then I tried using this nifty little port timing calculator:

http://www.modelenginenews.org/design/tcalc/TCalcForm.php

The only trick to using the tool was figuring out the distance from the top of cylinder that I mapped to and the crank center. Assuming a .5mm squish and measuring each piston, I came up with:

CRANK To Top of Cylinder Notes
Stock = 20mm (Half of stroke length), + 68mm (rod length) + 23mm (Piston offset) + .5mm assumed squish (approximately .020") = 111.5mm

Woodlands BB kit = 20mm (Half of stroke length), + 68mm (rod length) + 22.7mm (Piston offset) + .5mm assumed squish (approximately .020") = 111.23mm

Stock 066 Timing input and Results

066 with Woodlands BB cylinder and Piston Kit Timing input and Results

Being my first crack at this, I obviously could have messed up the calculation, but it seems like the inlet/outlet ports on the BB kit are pretty well opened up?

I don't really understand what the timing or differences in timing means here.

Any thoughts?

I'll post some actual port photos in the next post with some questions I have...

 

[Martinm210]

Reserve for photos:

Dome

Should I do anything about this or is it one of those you got what you paid for scenarios? Seems like one half is a little more rough than the other, is dome smoothness a big deal at all?

Transfer

Figured on at least polishing or smoothing out the transfers, are they supposed to be left rough? What about size/width?

Inlet

Seems pretty good in port size, figured on just smoothing the roughness?

Exhaust

Same here except polish to a mirror finish if I can. Is that how you're supposed to do it (rough inlet/transfer, polish exhaust?)...thought I heard that somewhere.

Piston

I don't like this piston, but this is all I could think of.
The picture of this BB piston looks more like the stock piston and of better quality, any ideas?
http://www.baileysonline.com/itemdetail.asp?item=PKS+B66&catID=378

Any thoughts or suggestions?
Thanks for looking and any guidance for this porting newb that I am..!..
Martin

 

[Martinm210]

Reserved for the after photos..

 

[Jacob J.]

A few issues....

First off- If you order the separate Big Bore 066 piston as listed in the Bailey's online catalog, you're going to receive exactly the same piston as what came with your BB kit. The picture in the online catalog is just a stock picture and doesn't represent the actual piston you would receive.

Second- your numbers in the model engine calculator appear to be fairly accurate. I have noticed there's slightly more blowdown with the Bailey's kit, although your stock 066 cylinder shows massive exhaust timing, much more than the early cylinders I've encountered.

On the roughness of the dome: Carbon build-up will quickly negate the casting finish on the dome. I've never worried about it, and I have BB saws that are going on two years in semi-daily service. Your thoughts on the ports appear to be good, cleaning things up, making things symmetrical, and smoothing + polishing that exhaust port will help.

You don't need to polish the transfers and intake, but you can if you want to do the work, you just won't see any huge gains from it.

Yes- match the intake manifold and the exhaust gasket-heat shield-muffler flange to your exhaust port.

 

[Martinm210]

A few issues....

First off- If you order the separate Big Bore 066 piston as listed in the Bailey's online catalog, you're going to receive exactly the same piston as what came with your BB kit. The picture in the online catalog is just a stock picture and doesn't represent the actual piston you would receive.

Second- your numbers in the model engine calculator appear to be fairly accurate. I have noticed there's slightly more blowdown with the Bailey's kit, although your stock 066 cylinder shows massive exhaust timing, much more than the early cylinders I've encountered.

On the roughness of the dome: Carbon build-up will quickly negate the casting finish on the dome. I've never worried about it, and I have BB saws that are going on two years in semi-daily service. Your thoughts on the ports appear to be good, cleaning things up, making things symmetrical, and smoothing + polishing that exhaust port will help.

You don't need to polish the transfers and intake, but you can if you want to do the work, you just won't see any huge gains from it.

Yes- match the intake manifold and the exhaust gasket-heat shield-muffler flange to your exhaust port.

Awesome, thanks!

I sort of figured if it's a woodland piston it would be the same, but if you have had good experience with the kit then I'll just run it, maybe some minor clean up of the burs on the piston skirt and call it good.

Good to know on the dome, I won't worry about it. There is a couple of burs left from threading I'll clean up, but leave it at that.

I wasn't sure on the timing calcs. I really had no idea if it was good or bad or what to really look for there, but since they both came out relatively close and the inlet and exhaust ports looked of pretty good size, that they are probably about right.

I'll keep at it, and post a couple of afters when I'm getting close.

 

[Martinm210]

Here are a couple of afters.

The intake I just clean up nicely and left it rough for good air/surface mixture.

The exhaust I spent the most time on, smoothing, then carefully sanding, much of which was hand work or using small needle files, then fine sanding, and polishing.

I also cleaned up all the burrs on the piston and polished the side ports.

I still have alot of work to do on the muffler/gasket/ exhaust port match.

The cylinder is now on, I may come back later and do more port work if there are some other gains to be had. For the time being I left the transfer ports. I need better tools before attempting something like that.

Checked squish with several gaskets, some of which I made. The .5mm metal gasket I had worked just about right. The metal gasket that came with the Baileys kit is way too thick and my .4mm paper gasket was too thin (.015"). In the end my squish was .020" on one side and .025" on the other using small pieces of solder to check with.

The saw is coming together slowly but surely, I have a few more parts to order yet, but nearly there. Also stripping, sanding, and repainting any of the major components. Case was already done, now working on the starter cover.

Fun little project.:biggrinbounce2:

 

[Lakeside53]

Ordering a separate piston - you might want to check.. the newer kits are "different"... and individual pistons could be from the old stock.

 

[Jacob J.]

You also might want to think about using different rings...there's been a number of failures on the new rings...Rings are cheap and labor isn't.

 

[Tzed250]

You also might want to think about using different rings...there's been a number of failures on the new rings...Rings are cheap and labor isn't.

Yeah, and with the price of a set of OEM rings the kit price will be getting closer to that of the OEM P&C.

I'm not sold yet.

 

[Jacob J.]

He can get OEM 395 rings that will fit that piston for $13 each. A new 660 top end lists for near $300.

 

[Wet1]

Thanks for posting this Martin.

Looking at your pictures, it does appear the transfers on the BB kit appear to be significantly smaller than on the OEM. Will you be porting them (the transfers)? Anyone see any reason not to?

 

[Martinm210]

Ordering a separate piston - you might want to check.. the newer kits are "different"... and individual pistons could be from the old stock.

Sounds good, I'll check with Bailey's and see if they can tell me.

You also might want to think about using different rings...there's been a number of failures on the new rings...Rings are cheap and labor isn't.

Didn't know that, but thanks for the heads up. I'll look into that.

He can get OEM 395 rings that will fit that piston for $13 each. A new 660 top end lists for near $300.

Good to know, I'll check into the 395 rings, my Stihl dealer also happens to be a Husky dealer too. Benefits of being in a small town I suppose.

Thanks for posting this Martin.

Looking at your pictures, it does appear the transfers on the BB kit appear to be significantly smaller than on the OEM. Will you be porting them (the transfers)? Anyone see any reason not to?

Yes, particularly the top transfers, but I believe that's much less important than the lower intake side. The piston skirt doesn't even touch the side width portion, so I figured on making some really nice wide chamfers on those bottom width port of the transfers. There isn't alot of mass in the casting behind it though, so there's not too depth will have to be kept down.

Thanks guys,
Any suggestions for places to order a 56mm piston from?

There were a couple of differences between this kit piston and the stock piston. The kit piston is a full 2mm tall which I think would do better in covering the exhaust port full at TDC. It also has a little more height above the piston pin, so porting would be different with a simple piston change if it was taller or different. I still don't understand what timing to look for, but going through the little calculator and thinking about the piston postions relative to the ports sure helps understand what changes things which is helpful.

I'd be interested in doing some timed cuts with this kit piston and perhaps another with some differences just to see if there are some tweaks. I don't like the looks gussets and structure of the stock piston myself, so I wouldn't mind changing it out.:dunno:

 

[excess650]

Your kit looks like mine, but your old piston doesn't look like the Mahle pistons that were in my old Mahle cylinders. The BB piston and my Mahle pistons are similar, except BB has 1mm wider skirt, and 2mm shorter. One old piston has smaller windows, and the other almost identical to the BB. The skirt on the BB is thicker.

BB piston weight 96g
Mahle piston A 89g
B 92g

BB piston pin 19g
Stihl pin 15g

I'm going to use a Stihl pin and open the windows further on the BB piston, and also bevel the inside of the bottom of the skirt. I doubt the material to be removed will exceed 1g. ***update - piston now weighs 94g after modification***

If I understood you correctly, your kit came with a base gasket, but mine did not. I have Bailey's 066 gasket kit, and it came with thick and thin base gaskets. The 1mm gasket will clear the piston, but makes the squish .050". The .5mm takes the squish down to .030", but won't clear the BB piston. It also has 4 notches cut into it from the bore side that decrease the contact surface, and its thinner than I would like at those points.

With the increased displacement of the BB kit, I would have expected the port sizes to be the same or larger than those on the(2) Mahle cylinders, but each dimension seems to be 1mm smaller on the BB kit.