Learned a lesson from ruining a Dolkita big bore P&C

40YearHomelite · Dec 11, 2012

I bought a DCS 6421 with the 84cc BB kit from Bailey's a little less than a year ago. I probably put about 10 hours on the 64cc and another 10 on the 84cc. I was recently bucking an old hickory when the saw suddenly lost compression and died. I gave a few pulls on the starter rope and the piston seized. F.

Now, when I say it seized, I mean it SEIZED. I had to strap the saw to a barn pole, strap a wench to another pole, and wench the cylinder off. This is what it looked like:

Apparently, the groove in the piston that holds the wrist pin circlip broke off, flinging bits of piston and circlip.

Thanks to Bailey's excellent customer service, I received a new BB kit free of charge. When I installed this one today, I made SURE to not gouge the piston, not strain the clip, and align the clip's gap at 12 o' clock.

While I was at it, I measured the squish at 0.051" with the metal base gasket for 150psi; 0.030" without the gasket for 165psi. I left the gasket off and sprayed on several layers of Permatex copper gasket compound. I re-tuned the carb and now the saw runs considerably stronger than it did last time with the gasket and lower compression.

Lesson learned: be careful with those dang circlips, align the gap at 6 or 12 o'clock, and go to Bailey's every chance I get :rock:

EDIT: pics of the broken circlip groove

ford832 · Dec 11, 2012

A little scuff with about a 220 grit and that will buff right out. :laugh:

There's been debate for years about aligning the open end of the clips.The general consensus these days is it makes no difference-but I still line mine up with the cutout.

watsonr · Dec 11, 2012

That thing is ugly, glad it worked out for you. Most of the site sponsors offer a warranty such as that one, not just Bailey's. The circlips in the new kit have a clip that was "C" shaped or more "G" shaped? Lots of guys are using OEM clips for the aftermarket kits.. just a question of which one you received.

Jacob J. · Dec 11, 2012

Part of your problem may be that you're using the clips that came with that kit. Bailey's hasn't upgraded the clips enough yet to where I'll trust them. I believe in the last BB 6401 I put together I used OEM 372 clips.

splitpost · Dec 11, 2012

ford832 said:
A little scuff with about a 220 grit and that will buff right out.
There's been debate for years about aligning the open end of the clips.The general consensus these days is it makes no difference-but I still line mine up with the cutout.

forget about where the cutout in the piston is,12 or 6 o'clock or you run the risk of popping a clip out

40YearHomelite · Dec 11, 2012

watsonr said:
The circlips in the new kit have a clip that was "C" shaped or more "G" shaped? Lots of guys are using OEM clips for the aftermarket kits.. just a question of which one you received.

Both kits I received were identical; they came with the "C" clips. Has anyone used "G" clips in a similar saw? From what I've read (with a grain of salt, though it makes sense to me), the "G" ones create too much imbalance to hold reliably without creating issues. They sure would be easier to install, though.

Jacob J. · Dec 11, 2012

splitpost said:
forget about where the cutout in the piston is,12 or 6 o'clock or you run the risk of popping a clip out

Husky and Stihl both recommend 12 o'clock.

brokenbudget · Dec 11, 2012

Jacob J. said:
Part of your problem may be that you're using the clips that came with that kit. Bailey's hasn't upgraded the clips enough yet to where I'll trust them. I believe in the last BB 6401 I put together I used OEM 372 clips.

it would be nice of they just supplied the oem clips with the kit instead of the mechanic wire they send out with them. this is the only real complaint i have with the kits from baileys.

Jacob J. · Dec 11, 2012

brokenbudget said:
it would be nice of they just supplied the oem clips with the kit instead of the mechanic wire they send out with them. this is the only real complaint i have with the kits from baileys.

I never use the piston rings supplied with the big bore kits either. Those "split ductile groove" rings or whatever can be very brittle. I always go with new Caber or OEM rings.

ford832 · Dec 11, 2012

splitpost said:
forget about where the cutout in the piston is,12 or 6 o'clock or you run the risk of popping a clip out

The cutaway is generally at about the 4-5 oclock position down.Having the ends at the cutaway engages the maximum surface area of the clip in the groove.
Most of the old two stroke tuners used to put the gap at the 6 oclock position,the theory being this would cause the circlip to expand under combustion whereas if you put the open end at the 12 position,the circlip tries to shrink under combustion.
Many of my 2t stuff over the years has come with the end gap in the cutaway,some have been wherever.
You read now mostly 12&6 and if you put it 3&9 the clips will "flutter"-maybe,but I'll still do it how I always have-I've never lost one yet.
I think really you can put it anywhere you like so long as you have a good,clean groove and a good circlip that hasn't been overcompressed.
When you think about the loads on the clip,I doubt position is a big deal-all things being equal.

BTW,that piston in the pic looks like a pretty crude casting around the piston pin area.

albert · Dec 11, 2012

The forces on them clips would surprise you. Anything other than 6:00 or 12:00 is asking for it.

ford832 · Dec 11, 2012

albert said:
The forces on them clips would surprise you. Anything other than 6:00 or 12:00 is asking for it.

How so?Assuming that an open section of the ring constituting maybe a 20th of it's overall circumference,what forces acting on this small open spot are going to cause the ring to collapse only in that position?Any side load is taken equally regardless of where the gap is.Is the thinking that compression pressure that blows by the rings would somehow unseat the clip in this position or slight pumping pressure from underneath?Explain please.

hotshot · Dec 12, 2012

High G forces

ford832 said:
How so?Assuming that an open section of the ring constituting maybe a 20th of it's overall circumference,what forces acting on this small open spot are going to cause the ring to collapse only in that position?Any side load is taken equally regardless of where the gap is.Is the thinking that compression pressure that blows by the rings would somehow unseat the clip in this position or slight pumping pressure from underneath?Explain please.

You always want the clip for to be symetrical (up or down) to the linear piston motion. The G forces are incredibly high when the piston suddenly reverses directions at 12,000 RPM, it would easily crush you or me if either experienced a tenth of it...

514mach1 · Dec 12, 2012

The lesson is never use those junky clips. I learned it with my 55 piston/cyl kit (ran about 30 minutes before clip took out the new piston and cyl). I've got the aftermarket clips in my 272 still, but they looked and fealt a lot more quality/solid than the ones with the 55 piston... so I'm not tearing the saw back down to change them to oem. The 272 piston is an NWP brand.

Mastermind · Dec 12, 2012

And this is the reason I only use Meteor pistons or OEM.

The cylinder casting and finish looks pretty good in those pics......the piston on the other hand is pretty rough.

As to the 12 or 6 o'clock position on the clips.....when I was in trade school many years ago that's what we were taught......

ford832 · Dec 12, 2012

hotshot said:
You always want the clip for to be symetrical (up or down) to the linear piston motion. The G forces are incredibly high when the piston suddenly reverses directions at 12,000 RPM, it would easily crush you or me if either experienced a tenth of it...

Thanks hotshot,I've heard that as well-that inertia will force the clip outwards from 12/6 whereas the clip ends could be forced together say at 3/9 and cause it to pop out.Given the mass of a circlip,I don't think this is actually possible that inertial forces would cause it to compress unless the clip was extremely weak or overcompressed when installed.
I've seen them installed in every position and torn them down to find them in all positions,and never seen an issue I'd attribute to clip position.
I was once told by an old engine builder that the reason for the orientation was to ensure people rotated them in the groove and thus seated properly.
I think what mastermind said is the most likely-it's what everyone was always taught-and so was I.

Learned a lesson from ruining a Dolkita big bore P&C

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