Stihl 084 build

[Stump Shot]

Was asked by our good OPE friend Alex @tspeedle if I would build an 084 for him, and after my best discouragement failed what he bought was on its way here. Now I say that knowing that there are others out there with experience with this model and myself not so much. So, this was going to be a learning experience for me. When the saw arrived it was only partially there and what remained was only partially good. I hadn't decided to do this at the beginning so I don't have great pictures to begin with but a few to give you an idea anyway. Note that what you see has not been taken apart by myself yet, rather how it arrived.

 

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The crankshaft needed to be replaced with a good used unit.

 

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From early on a Wiseco piston was desired and acquired which was compared to the old used piston and a new Stihl replacement piston. There was definitely a weight savings which seemed a good thing for such a large saw and be easier on the bottom end.

 

[hacskaroly]

Is the single ring vs. dual ring going to affect (improve or not) the saw in the end? Cool build, looking forward to seeing more!!

 

[Stump Shot]

I took some time for Alex to get the parts required to put this back together and it was decided to let Mike @Glock37 do his magic powder coating on the metal parts. Which he did and it turned out magnificently as always.



First thing to do was to install new studs so I could get it mounted up in my @tree monkey saw holder upper.

 

[Stump Shot]

Is the single ring vs. dual ring going to affect (improve or not) the saw in the end? Cool build, looking forward to seeing more!!

Yes, less friction.

 

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Next up is to get a new set of bearings on the crankshaft, which I do by the microwave method. Place the bearing in a wet paper towel and the microwave acts only on the wet toweling, turning it to steam which is the perfect temperature for the bearing to expand with zero chance for any damage, as it can only get as hot as steam is, about 212F. Note that a driver tool is at the ready just in case some extra encouragement is needed.

 

[Stump Shot]

Next up, getting it successfully installed in the crankcase. I like to heat up the case half and just drop the corresponding crankshaft bearing right in place. I've found over time that when placing the second half on it can get slowed up by the alignment pins. I solved this issue two ways. One, using a plastic hammer, give the second half a fairly smart rap with it when it gets to the pins, which puts it the rest of the way down. Then, for the second part, I use an old weak battery powered impact tool that won't get fasteners too tight, however between the speed and the rattles applied to the fastener upon tightening, the crankshaft bearings are free of side drag and does not require resetting upon completion as it's nice and free as it should be. As the screws were missing I found by looking at the IPL the proper length and that I had some from an 034 I had taken apart of about the same vintage and as I was already running it with some other parts, popped them in the ultrasonic to clean them off.

 

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Readying it for a piston.

 

[singinwoodwackr]

Having no knowledge on this model, I’m surprised at the piston rod. Never seen one of that.

 

[Stump Shot]

Having no knowledge on this model, I’m surprised at the piston rod. Never seen one of that.

Yes, it is unique enough, I would say it's fairly obvious to save weight of the reciprocating mass. Racer dude's use them building stroked 3120xp's into a 3140. I guess it's a thing.

 

[Stump Shot]

Now it came time to pick a piston, which I had the freedom to do, even though as it went some cheerleading for the Wiseco. Which had the benefits of saving weight, fairly important in this particular scenario, the Wiseco is also forged and is a tougher piston, and with one only running one ring geared towards high performance. One other advantage was the window size of the Wiseco. The new improved Stihl piston had extra weight which will soak up more heat, two rings which will give a compression advantage especially as it wears over time. Unfortunately, a smaller window than the piston it replaced, which tells me they went for more beef in the redesign.
This being not only just a rebuild and a bit of restoration it also is supposed to perform better. I decided to try out the Wiseco, but first check it out, just in case a reversal was in the cards, not just now, but maybe down the road as well. Then, upon fitting the Wiseco, a big negative reared up its ugly head. The bosses between the upper connecting rod were quite wide, wide enough to let the bearing slide out one way or the other a fair amount. This I absolutely did not take a liking to, as it turns out after talking to @Definitive Dave on the subject, this is as small a gap as can physically be had on the Wiseco forge. So, now the thinking begins, at first, going back with the OEM piston was a likely solution unless something could be done to correct the situation with the Wiseco...

 

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To keep things moving along some work on the sub-assembly's was in order.

 

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Problem encountered with the new pulley not fitting. Seems that the new/old model problem here.

 

[EFSM]

Now it came time to pick a piston, which I had the freedom to do, even though as it went some cheerleading for the Wiseco. Which had the benefits of saving weight, fairly important in this particular scenario, the Wiseco is also forged and is a tougher piston, and with one only running one ring geared towards high performance. One other advantage was the window size of the Wiseco. The new improved Stihl piston had extra weight which will soak up more heat, two rings which will give a compression advantage especially as it wears over time. Unfortunately, a smaller window than the piston it replaced, which tells me they went for more beef in the redesign.
This being not only just a rebuild and a bit of restoration it also is supposed to perform better. I decided to try out the Wiseco, but first check it out, just in case a reversal was in the cards, not just now, but maybe down the road as well. Then, upon fitting the Wiseco, a big negative reared up its ugly head. The bosses between the upper connecting rod were quite wide, wide enough to let the bearing slide out one way or the other a fair amount. This I absolutely did not take a liking to, as it turns out after talking to @Definitive Dave on the subject, this is as small a gap as can physically be had on the Wiseco forge. So, now the thinking begins, at first, going back with the OEM piston was a likely solution unless something could be done to correct the situation with the Wiseco...

View attachment 489709View attachment 489710View attachment 489711View attachment 489712

What size wrist pin is it?

 

[singinwoodwackr]

Now it came time to pick a piston, which I had the freedom to do, even though as it went some cheerleading for the Wiseco. Which had the benefits of saving weight, fairly important in this particular scenario, the Wiseco is also forged and is a tougher piston, and with one only running one ring geared towards high performance. One other advantage was the window size of the Wiseco. The new improved Stihl piston had extra weight which will soak up more heat, two rings which will give a compression advantage especially as it wears over time. Unfortunately, a smaller window than the piston it replaced, which tells me they went for more beef in the redesign.
This being not only just a rebuild and a bit of restoration it also is supposed to perform better. I decided to try out the Wiseco, but first check it out, just in case a reversal was in the cards, not just now, but maybe down the road as well. Then, upon fitting the Wiseco, a big negative reared up its ugly head. The bosses between the upper connecting rod were quite wide, wide enough to let the bearing slide out one way or the other a fair amount. This I absolutely did not take a liking to, as it turns out after talking to @Definitive Dave on the subject, this is as small a gap as can physically be had on the Wiseco forge. So, now the thinking begins, at first, going back with the OEM piston was a likely solution unless something could be done to correct the situation with the Wiseco...

View attachment 489709View attachment 489710View attachment 489711View attachment 489712

So…washers from HD?

 

[Stump Shot]

So…washers from HD?

Ah... no.

 

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What size wrist pin is it?

Hang on, we'll get there.