Big-Bore 56mm conversion questions!

[Cerberus]

tl;dr---- Are farmertec big-bores a comparable quality to their 54mm kits? Using Cabers of course, and ready to work crankcase appropriately....but if f.tec's 56mm isn't comparable quality to 54mm I'd be eager for reco's, maybe the duke's (don't want to go all hyway quality, as I'm porting/grinding almost every inch besides the plating ) What, in a word/statement, is THE BEST modification(s)/modification-type one can make on their saw to accomodate the 56mm jug & 99cc displacement?)

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So I've got a handful of Q's I've been unable to glean answers from google & forum threads yet so figured to post Will do bullet-point / line-items so people can answer what they know, if so willing ;D

#1 - Farmertec 56mm kits: are they comparable to the 54mm f.tec kits? If not, why/how? I ask because, while the f.tec kits need a lot of "casting imperfection remediation", I've found them to be otherwise-OK and would get one if I were going for a 54mm right now, but uncertain if I can just assume the 56mm kit is as-good(LOL, "as bad"?) as their 54mm kits....I don't mind working on it, just care Re plating & true-ness, and no f.tec jug has failed me there yet!!

#2 - IF f.tec big-bores are a no-go, how about The Duke's? Or do I gotta go hyway+? Don't get me wrong I love hyway, have a hyway popup kit in my better 660 (for now ) but I could've made a comparable jug from a $25 f.tec if I knew then what I know now (IE re altering bands & bases w/o lathes)

#3 - This'll put the saw at ~99cc,but - w/o crankcase modification - I suspect it'll create an "imbalance" among top&bottom halves of engine.... I know I have a thread that touches on this but **anything** on "How to work a 660 in-preparation / working-it-for a big bore kit?" would be extremely appreciated!!!

#4 - Port timing: I guess I would've assumed they'd just put the same darn ports as a 54mm, maybe enlarged like 4% (ie to proportionally enlarge in-proportion to the new larger jug), but keep hearing "You can freeport" which implies ports are NOT in same places as 54mm jugs) So yeah from watching for freeport (a usual f.tec 54mm jug leaves me like 60thou space on skirt before freeport )


So yeah that's the stuff I'm thinking of (OH by the way, these "Magnum" *44's/*66's are big bore right, that's what the "magnum" denotation means?), am pretty set on trying one of these big-bores and ready to order as soon as I find whether there's a lower-priced unit that's better than the f.tec ones that eccppautoparts sells on ebay (where I got my 54mm kit I'm very happy with!), for like $35 ($50 w/ your Cabers), otehrwise I think it's up to about $70 for the Duke's and >$100 for Hyway....kinda wish I could get a deal for buying hyway jug && f.tec 56mm slug!!)


Thanks a ton for any insight, am perusing threads and learning a ton (have watched all relevant youtubes on big-bores I could find!) but placing order tomorrow earlier in day at the latest so hoping to avoid a last-sec mistake in brand.....will go w/ the f.tec IF confirmed they're comparable to f.tec 54mm's, otherwise I believe I'll go w/ Duke (will call him 1st thing to see if his coatings' quality isn't top-notch, IMO the plating quality, and obviously the jug being true to the base-plate, are crtitical the jug is useless w/o them...)

PS-- do you really need to bore-out the (4) cyilnder-bolt holes to fit these on 660 crankcases? Do you need to mod the case more-than simply enlarging opening for piston so it doesn't scrape/bump when entering 54mm crankcase

 

[Jason628]

I was interested in the big bores as well but, have read many posts and talked to many ope members who say the BB's don't increase performance and can actually hurt performance. Most of it having to do with either freeporting issues or something to do with case volume not being sufficient enough to flow well. The intake tract for these saws are fairly small as well. Most of the "Duke" parts are sourced from the same place farmertec gets their parts. So... I would not be surprised if you order a cylinder from them and it is the same as the one you would get from farmertec. I would probably go with the hyway cylinder if I was to try one. They should be a direct bolt on. No modifying bolt holes.. I think I remember the post you are referring to and it was either a prototype jug or they were bolting it on an 064. The "magnum" badge is mostly a marketing thing. Some saws like the 038 had "mag" and "super" models that were larger than the base model 038.

My latest saw (660 #4) seems to run very well. I have a non modified 660 I'm going to compare it to. Then I'm going to take the non modified one down and do port work and a hyway pop-up.

 

[Cerberus]

I was interested in the big bores as well but, have read many posts and talked to many ope members who say the BB's don't increase performance and can actually hurt performance. Most of it having to do with either freeporting issues or something to do with case volume not being sufficient enough to flow well. The intake tract for these saws are fairly small as well. Most of the "Duke" parts are sourced from the same place farmertec gets their parts. So... I would not be surprised if you order a cylinder from them and it is the same as the one you would get from farmertec. I would probably go with the hyway cylinder if I was to try one. They should be a direct bolt on. No modifying bolt holes.. I think I remember the post you are referring to and it was either a prototype jug or they were bolting it on an 064. The "magnum" badge is mostly a marketing thing. Some saws like the 038 had "mag" and "super" models that were larger than the base model 038.

My latest saw (660 #4) seems to run very well. I have a non modified 660 I'm going to compare it to. Then I'm going to take the non modified one down and do port work and a hyway pop-up.

Such a great reply, and while 4 of them is cool I can't help wonder why? I have 2 myself but have a very anomalous case/reason for it (and they're both chinesium, and both "intentional play-things", I mean they're for-work but, with the wealth of knowledge online I've found, and the cheap&abundant parts, I can actually justify 'playing'!!

Very curious Re the comparison good luck, please update if you remember!! I also believe you're right Re it being from the 064 hybrid thingie (the one he re-painted, and put a d-handle on despite like low-20's squish), seen that youtube several times and do very much like his approach in fact the #'s for a top-end I'm building now is going to have nearly identical #'s (low 160's intake duration // exhaust around 99.5-100deg // 25.5deg blowdown // 21.5 squish from center-of-piston) How do you alter timing? I'm VERY new to this, my 1st porting was <1/2yr ago and, seeing me flail to a bigger saw despite insufficient funds, a/the head-honcho here on this forum gave me a unit he'd built (and had put the better part of $1k of OEM parts onto) but the unit hung a ring near-immediately so, having just done my 1st porting(my cs590), I didn't just buy a new top-end for it (as you describe, the hyway pop-up, great kit if you're using pop-up's/not maching bases for proper squish) but also bought a pre-assembled g666!
Will say I had ZERO complaints Re the Hyway kit, if told it were OEM I would probably have believed it (have spent a lotta time studying the OEM p&c, hell the jug in-general, have 2 on my nightstand right now rofl), thing is soooo great.....
Farmertec's....if not planning on doing major work yourself, I wouldn't advise running them (ie even a prebuilt g660 IMO should be taken apart and, at bare minimum, port's edges rounded (yup, rounded, not flat bevel/chamfer!!))
BUT of the 3 f.tec's I have, the plating looks great even at the top on ones I've touched the bands (by 16.5thou removed from one), and all 3 are "true" (base//band trueness, not cocked/misaligned/angled at all)
Duke's is Nikasil coated, and just looks nicer than the f.tec (I can PROMISE it's not an ftec, they've got what i can only describe as a "drywall 'Knock-down'" type of finish, like 5-7thou variance around the band from all the chaos, at minimum you'd almost have to sand the band at least (otherwise it'd be inviting preignition, which is very very bad, if you were running it at proper compression....wish I knew good comp.ratio or even psi for this saw (hate psi and squish as 'proxy' for compression but squish is just so easy to test!)

What kind of timing do you run? I'm uncertain how to "match" my units, maybe you've got a thought...of the two, I can choose whcih gets:
- the 25, or 32", b&c (RS33 chain, oregon & stihl bars, good quality stuff
- the 8-pin sprocket
- the big-bore jug at 25thou squish, or the 54mm jug running 28.5 squish with pop-up
- the 10thou removed key
- the 20thou removed key
I know I SHOULD be able to ^ immediately know "the best combo" with this stuff but am still stumped...am reading a book on 2-strokes now, hopefully get a good understanding, want to make my 660's as hot as can be while still being work-saws (still can't see how "very hot work-saw" is anything but "the least-warm hotsaw", fuels-aside I guess, though I'm still trying to learn Re hotsaws, not that I'd own one ever but for understanding how they gain their performance!

Re your objections to big-bores, itemized:
- the 2% volumetric increase (or nearer to 10%) it's hard to believe the intake boot would be a choke but would be curious if this IS substantiated (can't help but think of modded boots, if so -- I already round-off the inner-perimeter of the flange, just incase the match is one of those "100.0% no room for error" matches, like so many OEM muff gaskets though of course we mod those anyways)

- flow from crankcase would need to be bigger or you'd take a loss on top-end power, is my understanding, REALLY wish I knew if this was more like a 2% increase (that's the increase of bore, 2mm over 54mm..), or a 10% increase (the "nearly-100cc's" that big-bore guys say their 660 displaces) Gonna say my gut is it's closer to the 2%...which means a very manageable, not-so-significant "smoothing/flowing" of the crankcase, which IMO the 660 can use, not back-filling with JB and 'trenching' the case! Would of course be doing piston-window and transfer work to accomodate the higher flows! I have a good walbro carb on my 1st unit (thanks MM ) but still wondering "since I COULD turn-up the fuel, but not the diameter of the venturi(ie total flow/air), just how much more power can I fuel?" and don't know if it's closer to 10-15%, or 20-25% (on pump gas I mean, eth free, high quality and fresh but not jet fuel lol)

I'd love knowing swept/unswept gas volumes and any volumetric measurements anyone has, if any at all obviously, because if the big-bore jug is a 2% larger jug (though the larger piston would negate that so it's <2%), that's just the plated-part, I've no idea how they alter the chambers or if they do at all IE maybe they just do larger squish bands, reallly hope not but wouldn't shock me.. I wanna know this because, IF the cylinder swap adds 2.2% to the top-end, I don't know if that means I want to do a 2.2% removal (volume wise) on crankcase, or if I want to do a lil more...True/false: More crankcase volume means less low-end power, more high-end power?

Re freeporting...on my 54mm f.tec I have nearly 60thou before freeport -- I just cannot fathom that they are routinely placing the exhausts nearly 1/10th inch higher (if they're on threshold of freeport outta-box), otherwise it's just removing like 5 or 20thou from base so your squish & compression are at an appropriate level, OEM's enlarge squish to account for intolerance-buildup during production, but for any particular unit you can check its actual squish, and then move it to appropriate which I think is 20-30 for this saw depending who you ask...people say don't go <20thou but I've yet to hear anecdotes of piston-slap, just that "it could happen", makes me wanna bet that many say 60cc units could get away with 17-18squish which would be significant it's closing-up over 10% of the squish-gap which has a real effect on combustion / thermal efficiency!)

 

[Cerberus]

IF one is altering band, ports and base, I'm thinking the biggest difference may be the chrome-v-nikasil plating, would love to hear thoughts on this!! I heard recently "all new saws are nikasil" but swore I've seen spec sheets saying chrome (are piston-tops ever chromed, or any part of a piston? I do mean chrome not molyB or soemthign )

Think that chrome is supposed to be easier to work with when doing your port-edges? But just how much quicker will it wear-out? I had excessive wear on a molyB coated piston on my last build of my blue Holzff but what's driving me nuts is that, while I cannot see it, the wear to those elastic/pressurized piston rings must be far worse!!! Literally ordered a new 54mm set of Cabers when I saw that, like instantly lol, and already ordered the 56mm Cabers for the big-bore kit (I'm going to go for it, IF I cannot make it work then cest la vie, but - since I cannot think of 1 legit reason it can't be made to work, I wanna try!!), am gonna order a big-bore kit I just realize the biggest fears - plating quality, freeporting, and not-true cyilnder - are all things I can likely suss-out pretty immediately, before use, and just return it (ebay, will probably order from eccppautoparts again, so f.tec., they don't state it but that's what they sent me for a 54mm recently, besides typical "moon-surface" finish on squish-band the jug was outstanding, and I should mention their newer pistons have >1mm wider, per side, skirt-flares on exhaust-side ;D )

 

[Wanab]

At this point I would say avoid the Hyway as both jugs and pistons I have received from them are not serviceable in stock form. So far in my research the Farmertec stuff is better than the Hyway.

 

[Wonkydonkey]

Holy *s-word,,


you been on that pipe

 

[Ronie]

I put a big bore on that Neotec clone and it's a turd, torque is ok but it's slow. I put an OEM one my Farmertec kit saw and it's faster in the cut and pulls better. I bet if you put a want ad up and kept a look out on ebay you could find an OEM one.

 

[Cerberus]

At this point I would say avoid the Hyway as both jugs and pistons I have received from them are not serviceable in stock form. So far in my research the Farmertec stuff is better than the Hyway.

WOW that's interesting, can others chime-in on this? I was actually taken-aback by the quality of my Hyway kit (54mm w/ pop-up, w/ Cabers), the f.tec kits on the other hand have (all 3 of mine exhibit these flaws) have:
- Ports: platings' ends are garbage; Port shapes are chaotic & asymmetrical; Even port placement can be worrisome from what I hear (I've avoided that, thankfully)
- Squish-bands are just AWFUL, my hyway's band is nice & smooth, and that's what I've seen on other hyway jugs....but I have (3) F.Tec jugs and 1 thing that's a constant is the pock-marked squish band, are you seriously saying you've got f.tec jugs w/o "textured squish bands"? My 3 are from: ~2.5yrs ago, maybe 1yr ago, and from a g6660 built in July this year by Holzff

Very curious to hear if you've gotten (or even seen) f.tec jugs w/ good, smooth squish bands, that's not at all what I've seen (I have pics if they'd help, think I was clear enough!)

I'd put a hyway jug in a saw & be comfortable running it (OK maybe I'd prefer 5-10min to refine the lowest-hanging fruit, but even OEM is not w/o flaw!!), but would NEVER run an un-touched f.tec jug now that I've seen this on all 3 of the units I have (am guessing yours have this, but you're probably cutting the band ergo overcoming that defect...but so am I )

 

[Cerberus]

Holy *s-word,,


you been on that pipe

HECK YEAH (we're referring to the phenomena of getting&keeping your saw @max RPM through a cut, right? Hear Tinman use that terminology 'on the pipe', too sloppy a term IMO :/ )

/yes I'm aware of your actual meaning, and no I actually can't do anything of that nature my body doesn't tolerate it I have not had, cumulartively, 1 single drink in the past 2yrs (I've had maybe 2 or 4 times I "got a drink" but never had more than a single/few small sips), it SUCKS I loved alcohol (perhaps too much NO definitely too much) when younger and then, like the better part of a decade ago, suddenly working w/ any hangover (here in FL) became so hard that it created a 'negative pavlovian conditioning' (I'll get some nausea when having 'tongue wetting' "sips" the rare times I'll take a glass of champage/beer/whatever, thankfully I've no social life so being a non-drinker is OK ;D))

//pretty sure it's obvious I do have very severe ADHD, am striving to do better and typically not submitting a post w/o 1-2+ reviews of it first! lol at the idea of being all intoxicated &playing w/ chainsaws though, that is a dangerous but....hate saying it...kinda funny thought, immediately think of "chainsaw fail" youtubes

 

[Jason628]

I don't have enough finger strength to hit on everything but, I go with the KISS mentality. I started documenting my own builds so I can look back on what works and what doesn't. The first saw I built I didn't alter port timing. Can't remember what it was... I know squish was about .018 and it had a pop-up in it. I sold it and made $175 and shortly after it snapped the cylinder screws. Second saw I gave to my dad. It had same squish and same cylinder and piston and .015" off key. Didn't alter port timing. I just evened out and chamfered. He has yet to really use it. Third saw is all stock with port chamfers and didn't measure squish. It runs ok. I built it primarily as a sort of "base line" #4 has pop up, widened ports, dropped transfers, .020 off key, and a dual port. Have yet to really run it but, made a few cuts with the grain on some big pine rounds and it did not put a noticeable load on the engine. The farmertec jugs vary in squish and port timing but, I have not gotten a horrible one yet. One thing i will say is they are very easy to carve out and haven't had any plating issues as of yet.

 

[Cerberus]

I put a big bore on that Neotec clone and it's a turd, torque is ok but it's slow. I put an OEM one my Farmertec kit saw and it's faster in the cut and pulls better. I bet if you put a want ad up and kept a look out on ebay you could find an OEM one.

OEM 56mm? With what OEM costs I can't imagine ever paying for it, had been watching a P&C (used) combo for nearly$300 on ebay several weeks back, honestly I just don't see the AM top-end kits as the "worry spot" for chinesium in this case (because the problem areas are areas we're gonna be refinishing anyways, so I just care about plating and the "true-ness" of the cylinder to its base-plate, both of which have been stellar in the 3 ftec's I've inspected!!

Re your neotec (hehe I still haven't read that thread, waiting for when I can read at least 30min to start it / realllly wanna absorb your approach/thinking!!), and finding "torque is OK but it's slow", I've got a couple Q's:
- 7 or 8 pin sprocket?
- ignition timing, is it OEM? IF 'yes', 2nd question: is your comb.chamber lower than it was? If so, timing needs to be advanced to 'match' what it was when the spark plug sat physically higher (ie before cutting a base or removign base-gasket)
- do you use a muffler that allows atmosphere to thoroughly intermingle with the exhaust-charge in your muff (IE around the area of the exhaust-flange, inside that muff)?

Can I ask what porting #'s you'd used on these 2 builds? IE, if you messed up and were dealing-with 175 deg intake duration because you'd ported intake port and lowered cylinder, could greatly hurt things..so am curious if, of these 2 top-ends you compare here, are they ported the same, wearing comparable mufflers, and running comparable compression (and appropriate intake-timing)?
Because each of those that varies from optimal will begin de-optimizing, of course...

Big bore ktis mean more top-end displacement, which should mean better low end power (whereas exaggerating the crankcase::cyilnder volumes ratio should boost high-end output), so they "change the balance" of top-end // crankcase volumes, relative to one another, which needs correcting!! I'm trying to figure-out the volume/displacement of the crankcase, so that I can port/trench/flow my case a proportionately-larger size to accomodate the larger top-end (though I'll be erring towards a slightly-lower-than-matched displacement for crankcase, since again "bigger crankcase, relatively, means peak power is at higher RPM)

It's almost funny because I'm still struggling VERY hard deciding which 660 gets what, when I have the options:
- key advanced 10thou & a key advanced 20thou ignition timing
- fullwrap & halfwrap bars, and 25" & 32" b&c combos (good bars, rs33 chains)
- 7 & 8 pin sprockets
- "high RPM / modest torque" type of built 56mm top-end.....or 54mm VERY high-compression top-end
^ Those are things that I know there's "good and bad ways to mix them" but I'm just floundering trying to figure-out which unit I'm doing which to Think that, since the blue one's weaker crankcase, that I'll do the big-bore (higher speed, lower compression) top-end setup on that guy!! Actually about to begin porting the case momentarily anyways, even w/o a big-bore kit the case//jug match-up was terrible!

 

[Wanab]

Big bore kits in saws don't work because they reduce port area and move the timing in an unfavorable direction. The only true big bore 2 strokes with a very few exceptions that are all around better and not just moving the power around are complete cylinder replacements that are physically larger. My dealer quoted me $400 for the OEM kit.

 

[Cerberus]

Big bore kits in saws don't work because they reduce port area and move the timing in an unfavorable direction. The only true big bore 2 strokes with a very few exceptions that are all around better and not just moving the power around are complete cylinder replacements that are physically larger. My dealer quoted me $400 for the OEM kit.

WHOA I had NO idea there was an OEM big-bore "kit" if you can find a part# or link or name or anything it'd be hugely appreciated, google is not helping me here!!

Would LOVE to see how Stihl approached it (I guess my understanding was that it is inherently "more than a kit" since the main "accommodation" for it is matching the crankcase IE porting it so your displacement 'ratio' between upper&lower ends does not change, at least not in a pro-cylinder direction, because that pushes peak HP to a lower RPM, whereas higher crankcase displacement, relatively, helps push peak-HP to higher RPM's, is my understanding!)

So eager to see how Stihl approaches it!! I now see that the pistons themselves are like 2mm short, which would make the intake duration impossibly large w/o JB weld'ing it, had thought you "had" to do the crankcase just to use a big bore kit which is not the case w/ the chinese ones so I'm VERY eager to see what Stihl does for "big bore"!

Couple specifics I wanted to make sure I understood you on:

"they reduce port area"
Because a 56mm jug has the same port shapes&heights as a 54, ergo they're smaller relatively speaking? If so, this is of course remedied by port-work, and -for this jug- the smaller the intake from teh factory, the better, right?


"Moving the power around"
Because of higher cylinder displacement, relatively? This is not an issue if you also port/flow the crankcase proportionately, right?


"move the timing in an unfavorable direction."
I'm struggling to understand this one, wouldn't timing be identical since nothing is changed 'vertically', everything is lateral/fatter, stroke and chamber-height are maintained so wouldn't timing be maintained? I'm thinking of spark/ignition timing maybe you mean something else entirely?

Thanks for any elaboration, and for mention of OEM varieties here, that is so cool to hear I can't wait to see the specs/details!!

 

[Mastermind]

WHOA I had NO idea there was an OEM big-bore "kit"

There is no OEM big bore kit.

 

[Cerberus]

I was going to make a thread but fear it'll be met the wrong way so gonna squeeze it in here...

Any pistons from other saws that would fit a *66 powerhead, but in 56mm bore? When I say "fit" I, of course, do not mean a direct, no-work fit, I guess I mean whether it'll fit the connecting rod, and have skirts at-least as tall as an OEM 54mm piston would (these big bore kits' pistons are made shorter so people can do "bolt on" installs w/o working the crankcase, which of course destroys the intake timing...piston swapping could overcome this and I know I've heard of it, so figured to ask!)

There is no OEM big bore kit.

Was there ever any "Stihl big-bore" anything, like a 400/600 series variant/option in big-bore? I would've guessed a hard No, but if there is I'm beyond eager to see how they'd approach it!!

 

[Cerberus]

And not addressing what "work" you were referencing earlier...have to imagine you mean the obvious, Occam's Razor and all, and readily admit I'm aware that it probably seems silly to all of you that I'm doing all this on-purpose (and even 'for fun'), but it's fun for me, I get to play w/ them like an adult Erector Set while simultaneously having at least (1) 660 ready-to-go at any moment, and the backup parts if anything went wrong with it, and the increasing talent/capacity for working on it proficiently.

Have every intention of doing a whole lot more w/. these, I don't have a "finish point" in mind just yet (getting close though ;D)

 

[Mastermind]

Any pistons from other saws that would fit a *66 powerhead, but in 56mm bore?

I did a 56mm jug using a 395XP piston. Complete waste of time and energy. The OEM 54mm top end wound up much stronger.

 

[Mastermind]

Was there ever any "Stihl big-bore" anything,

There was a 038AV then Super....then Magnum. Each is 2mm bigger. They did the same on the 056, and on the 034 then did an 034Super than was 2mm bigger.

 

[Mastermind]

If you really want one of these saws to perform. Get an oem top end for it. Have that top end ported by a pro.

 

[Wanab]

Because a 56mm jug has the same port shapes&heights as a 54, ergo they're smaller relatively speaking? If so, this is of course remedied by port-work, and -for this jug- the smaller the intake from teh factory, the better, right?


"Moving the power around"
Because of higher cylinder displacement, relatively? This is not an issue if you also port/flow the crankcase proportionately, right?


"move the timing in an unfavorable direction."
I'm struggling to understand this one, wouldn't timing be identical since nothing is changed 'vertically', everything is lateral/fatter, stroke and chamber-height are maintained so wouldn't timing be maintained? I'm thinking of spark/ignition timing maybe you mean something else entirely?

Thanks for any elaboration, and for mention of OEM varieties here, that is so cool to hear I can't wait to see the specs/details!!

You have some things correct. There is no room to improve the smaller jug enough in many cases. Why you need new jugs when you go big bore.
Anytime you move more CC's (or less) through the same size,shape port timing it changes the powerband.
The ports are angled and the larger bore changes the height.