parts saw Dolmar PS-7900 re-build

[meglodon]

yeah, the AM stuff is def not as quality as OEM. I was thinking more on the checking fitment without being out the cost of OEM right off the bat. If you have a chance to check on your side I would appreciate it!

 

[meglodon]

No joy on the bolts locally. Redneck ingenuity to the rescue while I wait for the ones I ordered to show up. How does the saying go? if it's stupid but it works... is it still stupid?
I bought some 8/32 rod, cut two 59mm size pieces & threaded one end to the 4mm size, double nut locked two 8/32 nuts on the other end, ground them down to fit inside the air horn piece and hacksawed a slot for a flat head screwdriver. Anyway, that pulled everything together nicely.

Enough to successfully get it to start, run & revs quick! Sounds good, seems strong.
Blipped the throttle and ran it for a few minutes, turned it off and restarted, it seems to run well. Although the idle is a bit higher than I'd like. (Showing 3k on my tach and turning in the idle adjustment didn’t have a big change.) I know the carb was suspect and may have other problems than the springs being broken. I’ll have to investigate a bit more once it cools down a bit, I’ll pull the spark plug and check the cylinder out then re-check the jets on the carb.

But. It started & restarted so that's a small victory by itself!

 

[Lightning Performance]

yeah, the AM stuff is def not as quality as OEM. I was thinking more on the checking fitment without being out the cost of OEM right off the bat. If you have a chance to check on your side I would appreciate it!

Just find out if the Dolmar and Makita interchange on the crank size.
If you get that number we can figure out the rest.
Other companies used drum drive setups maybe not all plastic. So consider the 026 bronze drive gear. The 181-281 and up won't work, too big. Now everything else can be cut, glued, adapted or otherwise on the drive arm. Plastic was eventually chosen because of vibrations and weight plus costs. Stihl added a spring for improved wear. The oil worm doesn't know the difference so keep that in mind. On the milling saws I'm using a different pump system now moving forward. I ran out of room so it had to change once the stroke got bigger.

The good part is your not turning a high volume modified pump. The great news for me was no more oil pump issues with no gears in there. This should be a fairly easy fix once you get a part to fit your crank and possibly your stock pump assembly.

 

[meglodon]

Just find out if the Dolmar and Makita interchange on the crank size.
If you get that number we can figure out the rest.
Other companies used drum drive setups maybe not all plastic. So consider the 026 bronze drive gear. The 181-281 and up won't work, too big. Now everything else can be cut, glued, adapted or otherwise on the drive arm. Plastic was eventually chosen because of vibrations and weight plus costs. Stihl added a spring for improved wear. The oil worm doesn't know the difference so keep that in mind. On the milling saws I'm using a different pump system now moving forward. I ran out of room so it had to change once the stroke got bigger.

The good part is your not turning a high volume modified pump. The great news for me was no more oil pump issues with no gears in there. This should be a fairly easy fix once you get a part to fit your crank and possibly your stock pump assembly.

I had to place an order for a part for my buddies saw from HL Supply, so threw a 026 oil pump gear on there to check it out. We'll see how it works.

Otherwise, a bit of tweaking with the carb and it seems to be holding around 2800-2900 at idle (which isn't terrible) I'll run a couple tanks off and on while I wait for this drive gear to show up.

Depending on how it fits (or not) I have been thinking about how I might be able to swap the top plastic portion as that appears to be the wear piece. I've got a lathe so I may put it to use to build an aluminum collar or maybe full piece that I can press the center bushing into.

 

[Lightning Performance]

I had to place an order for a part for my buddies saw from HL Supply, so threw a 026 oil pump gear on there to check it out. We'll see how it works.

Otherwise, a bit of tweaking with the carb and it seems to be holding around 2800-2900 at idle (which isn't terrible) I'll run a couple tanks off and on while I wait for this drive gear to show up.

Depending on how it fits (or not) I have been thinking about how I might be able to swap the top plastic portion as that appears to be the wear piece. I've got a lathe so I may put it to use to build an aluminum collar or maybe full piece that I can press the center bushing into.

K.I.S.S.
Brass maybe your new friend if you find a worm and arm type assembly that can run in your gear. If not alter your worm gear for a Stihl spring arm. Let me know when your finished. I'll take three.

Have a Makita gear with a cracked arm on it waiting for an AM update.

 

[ballisticdoughnut]

I’ve got a local Makita dealer that can order Dolmar/Makita chainsaw parts. I’ll call and check on availability of the worm gear.

 

[meglodon]

K.I.S.S.
Brass maybe your new friend if you find a worm and arm type assembly that can run in your gear. If not alter your worm gear for a Stihl spring arm. Let me know when your finished. I'll take three.

Have a Mikaya gear with a cracked arm on it waiting for an AM update.

I'll keep you posted with the findings

I’ve got a local Makita dealer that can order Dolmar/Makita chainsaw parts. I’ll call and check on availability of the worm gear.

That'd be awesome if you have time!

 

[Lightning Performance]

I'll keep you posted with the findings

Sure

If you can find an undersized gear they might be worth looking into if it can be bored bigger. I can check the crank on the Makita with A type 1125 worm gear.

Edit the 1135 and 1128 are the same inside. The 1125 might be different. Stihl used the same gear pitch on most of the worm spring drives.

 

[meglodon]

I'm investigating some piston slap I hear at idle, Not what's causing it, the bore of the cylinder might be a bit clapped out for the piston I have, or something is up with the squish (the piston had some build up on it) more to come as I investigate that.

While that's in play, I’ve made some progress with the oil drive gear. The 026 gear fits the shaft and has the same gear thread

I chucked up the 372 drive piece in my lathe and bored out the center of it to match the outer diameter of the 026 drive gear.

Put things together and from the test fit it looks pretty close.


old vrs new


I added a bit of wire around one portion of the 026 metal drive part, cut a bit of a trench and drilled some holes for JB weld to go through, compressed the whole thing together and letting it setup.

The other thing that I'll need to do is trim the outer arms to fit through the brake band and match the clutch diameter (it's just a bit big) but i'll do that once things harden up and set. I'm also planning to plastic weld the other to give the bond a bit more strength.

 

[meglodon]

Bit more work to do tonight, but I think it'll work pretty decent.

 

[oldpartsinasia-joe]

I have those highlighted in green.... on paper. If you are keen, let me know which ones and I re-confirmed in the actual stock.

-oldpartsinasia Joe

 

[oldpartsinasia-joe]

and if you are still looking at the screw that secure the carb...
and a new connecting muff (item 47) not highlighted
-oldpartsinasia Joe

 

[meglodon]

I have those highlighted in green.... on paper. If you are keen, let me know which ones and I re-confirmed in the actual stock.

-oldpartsinasia Joe
View attachment 1058386

Nice! Depending if you have them in stock (and on the cost + shipping) I would be interested in 131 (the oil pulley gear) & two 35 (the carb bolt spacers)
I appreciate you checking.

Because... My test fit of the home-made drive pulley has interference with the oil pump, unfortunately the metal drive arm hits so I'll have do some more work there.

In terms of the sound I'm hearing, it's in the bottom end (still is there with a different cylinder and piston on it) I think there is something not aligned 100% so when I have some time I'll be tearing things back apart to see what isn't right...
(hey at least it's clean)

 

[oldpartsinasia-joe]

Here are the parts that you might need.
Oil pully gear spacer and the original carb screws.
PM me your postal code and will work out the cost of shopping and parts.

Definitely the cost of shipping (USD 60 to USD110) is more than the cost of parts. Any part numbers that you need, just let me know.

-oldpartsinasia Joe

 

[Lightning Performance]

Nice! Depending if you have them in stock (and on the cost + shipping) I would be interested in 131 (the oil pulley gear) & two 35 (the carb bolt spacers)
I appreciate you checking.

Because... My test fit of the home-made drive pulley has interference with the oil pump, unfortunately the metal drive arm hits so I'll have do some more work there.

In terms of the sound I'm hearing, it's in the bottom end (still is there with a different cylinder and piston on it) I think there is something not aligned 100% so when I have some time I'll be tearing things back apart to see what isn't right...
(hey at least it's clean)

Was thinking about the all brass gear that fits the 024/026 plastic none adjustable oil pump.
I just happen to have one here apart to measure the drive gears installed height. How convenient

It has no spring attached to that type. Now that you have a near working assembly I see the problems. Going with a taller worm gear or adding a shim washer behind it gets you off the pump housing. Really no need for the spring to be behind the plastic part. You don't need the plastic arms if the worm spring engages the drum. Using one or the other should work fine. I've had little time to get all these parts and a Makita on the bench to measure those drive parts to see if the cranks match. They could be different from yours and are becoming harder to source parts for. The pumps seems to last a good long time. These are all stuff like tires and brakes, expendables.

Good start on setting up a prototype. Trying solder on the other drive might just work or a different worm assembly. I have some 1125 Stihls to be assembled. The 2186 Jred parts are all too big to work in this assembly. I've eliminated a few that need parts.

 

[Tractorsaw1]

Looking for a 131 oil pump drive - what’s cost shipped to 63351

 

[meglodon]

Thanks to @oldpartsinasia-joe on the first round I used the approach of heating the bearings and slipping onto the crank, then heating the cases to put things together. I was able to get the drive gear & carb bolt/spacers! Thanks so much, I really appreciate your help on this and it gave me the incentive to dig back into this project.

So I accumulated addtional parts I thought I may need to re-rebuild the lower end (bearings, case gasket, etc) and spent yesterday ripping apart the saw to determine what was causing the noise in the bottom end. I forgot to take pics this round but found that the flywheel side bearing cage had failed. It was the melted plastic which was causing it to not spin freely. The clutch side bearing is perfect (both had plastic bearing cages.)

I pulled the clutch side and although I had the replacement nylon caged bearing, I decided to re-build with a steel cage 6202 bearing I had for another project. I checked the specs and the measurements showed they are exactly the same apart from the bearing cage. I guess we'll see how it goes.

I also changed how I pulled the case halves together, on the first round I heated the bearings and slipped them onto the crank, then heated the cases to put things together. This time I used heat to get the case to 275-280ish and dropped the bearing in, then I used some tools that attached to the crank to pull the case halves together.

I am much much happier with the way things turned out, the bearings spin smoothly without any noise.

Then I put everything back together (with the aftermarket 54mm big bore kit.) Let the sealent sit overnight and just fired it up. The noise I heard is no longer there! But it's 23 degrees with a windchill of about 0, so I have elected to continue testing another day.

Thanks again @oldpartsinasia-joe!

 

[oldpartsinasia-joe]

Hi meglodon, glad you managed to continue the project! All I did was to match what I had to what you need!


-oldpartsinasia Joe

 

[meglodon]

Ok, a bit more of an update. Saw was dying at idle but I went through and tweaked the Low and High idle screw side of things and have the saw in a good spot for break in. Idle holds at about 2750, when you get on the throttle it's fairly instant and revs to about 12,900 - 13,000 (I didn’t leave it up here for more than a second or two blip) I’ll run a tank or two at idle 15-20 minutes at a shot interspersed with a few revs to blow out any oil build up.
I’m looking forward to getting a bar and chain on it and testing it out in some wood to see how it cuts.

 

[Tractorsaw1]

Ereplacement parts has new oiler drivers for $20