Pressure testing a Dolmar 5100s - what am I doing wrong

[sevensandeights]

2008 Dolmar 5100s. Great saw, owned since new, well cared for and has been used to cut about 60 cords (full, not face) of firewood. Starting to notice loss of power in the cut and erratic idle but saw does start and run. Stock saw that runs a Dolmar 18" bar and 3/8ths chain (64DL). Carb was "upgraded" to different model Zama that was recommended to me by the guys at Cutting Edge a several years ago that helped my symptoms initially but they are much worse now. Intake boot has the metal insert ring that was added by the factory.

I initially posted about this problem back in 2020 and everyone said to pressure/vacuum test. I didn't have the proper tools at the time so I "solved" problem by getting a new saw! However, I miss running the 5100s so I started tinkering with it again and would like to try and fix it. I do now have pressure tester and have used it on one other saw in the past.

I put a piece of rubber between the intake boot and carb and and muffler and cylinder. I also made custom block off plates to make it easier to see things without the carb/muffler in the way. Mityvac pump connected to impulse nipple. I can't get the saw to hold any pressure at all with either the muffler/carb or block off plates. Checked the Mityvac and it creates pressure when I occlude the nipple.

What I missing? If I'm not doing anything wrong and the saw has this big of a leak, what is the likely culprit? The most saw work I have done has been to change a P&C on a Dolmar 6400 to make it a 7900. Not sure how to get access to the various seals that could be leaking.

 

[link]

@ cuinrearview

 

[lone wolf]

Strip it down on the left and right sides so you can see both crank seals ,you need the flywheel off and everything then get a spray bottle of soapy water and spray everything while putting pressure in to look for a leak. If that don't work dunk it in a bucket of water while putting pressure in till you see the leak then remove quickly.

 

[sevensandeights]

Ok - no turning back at this point. Any tips on how to get the flywheel and clutch off?

 

[sevensandeights]

Made some progress but I don't have a piston stop tool nor could I find a piece of rope anywhere! Have to go to a wedding out of town tomorrow so I ordered a stop tool and it will be here by Sunday.

I got the clutch off (used an impact on the nut before I read that a shouldn't do that). Made a clutch removal tool but couldn't stop the piston so that will have to wait. I was able to spray soapy water on everything I could see so far - intake boot, part of the base gasket, flywheel side seal - no bubbles and still not holding any pressure on the Mityvac.

Dolmar repair manual I found online mentions putting a "wedge" in the exhaust port to block the piston. Has anyone done that over using something in the spark plug hole?

 

[J D]

That doesn't look quite right

 

[J D]

While I'm not particularly familiar with the 5100 I've seen a few saws that threaded portions of the crank case went all the way through & would cause a significant leak if there wasn't a screw in em

 

[lone wolf]

Ok - no turning back at this point. Any tips on how to get the flywheel and clutch off?

Made some progress but I don't have a piston stop tool nor could I find a piece of rope anywhere! Have to go to a wedding out of town tomorrow so I ordered a stop tool and it will be here by Sunday.

I got the clutch off (used an impact on the nut before I read that a shouldn't do that). Made a clutch removal tool but couldn't stop the piston so that will have to wait. I was able to spray soapy water on everything I could see so far - intake boot, part of the base gasket, flywheel side seal - no bubbles and still not holding any pressure on the Mityvac.

Dolmar repair manual I found online mentions putting a "wedge" in the exhaust port to block the piston. Has anyone done that over using something in the spark plug hole?

Yes you can use impact I always do. Dunk it in water and you will find the leak real fast.

 

[sevensandeights]

JD - it's hard to tell from the pic but that's just the gasket sticking up. Looks like a void in the picture but it isn't. Sprayed soapy water there and no bubbles.

Tinkered just a little this morning. Tried just blowing in the Mityvac tubing rather than using the tool to build pressure. Slight resistance but really couldn't build any pressure. Suction provided the same result. Slight resistance but significant vacuum leak. Did that again while listening for a leak and seems to be coming from behind the clutch. Will see tomorrow after I get it off.

I checked the flywheel and the "key" is still there as is the indentation on the shaft so should be no issues with realignment/timing.

 

[lone wolf]

JD - it's hard to tell from the pic but that's just the gasket sticking up. Looks like a void in the picture but it isn't. Sprayed soapy water there and no bubbles.

Tinkered just a little this morning. Tried just blowing in the Mityvac tubing rather than using the tool to build pressure. Slight resistance but really couldn't build any pressure. Suction provided the same result. Slight resistance but significant vacuum leak. Did that again while listening for a leak and seems to be coming from behind the clutch. Will see tomorrow after I get it off.

I checked the flywheel and the "key" is still there as is the indentation on the shaft so should be no issues with realignment/timing.

Dunk it and we can go from there! Takes a couple minutes is all.

 

[TRTermite]

Dunk it and we can go from there! Takes a couple minutes is all.

I usually have the ignition off before I dunk one. Maybe paranoid and you Probably have it off to see the
flywheel seal. Keep pumping pressure into the saw and water won't get in. I agree with Lone Wolfs' notions.

 

[lone wolf]

I usually have the ignition off before I dunk one. Maybe paranoid and you Probably have it off to see the
flywheel seal. Keep pumping pressure into the saw and water won't get in. I agree with Lone Wolfs' notions.

Well yes to take the flywheel off, impact the nut off, then hold the saw up by holding the flywheel then strike the crank end with a brass drift shaply ,use brass or lead not steel or damage will occur.

 

[sevensandeights]

Unfortunately no time to mess with it any more today. Other bad news is it looks like the clutch side seal is going to be hard to find. Found one place that has it in a combo pack with the bearing but everywhere else I have looked is out of stock. Any suggestions on where to get parts for these saws? No dealer within 100+ miles from me.

 

[lone wolf]

Unfortunately no time to mess with it any more today. Other bad news is it looks like the clutch side seal is going to be hard to find. Found one place that has it in a combo pack with the bearing but everywhere else I have looked is out of stock. Any suggestions on where to get parts for these saws? No dealer within 100+ miles from me.

@fordf150

 

[lone wolf]

Unfortunately no time to mess with it any more today. Other bad news is it looks like the clutch side seal is going to be hard to find. Found one place that has it in a combo pack with the bearing but everywhere else I have looked is out of stock. Any suggestions on where to get parts for these saws? No dealer within 100+ miles from me.

We dont know if that one leaks yet so don't wreck it till you find another.

 

[Jay Hansen]

If it's leaking that badly you can usually find it immediately by blowing smoke into the tube and see where it comes out.

 

[pele55]

We put clutch side crank seals in those all the time. They are known for it

 

[L34]

If leaking bad I use my compressor set to about 5psi on the reg.
This gives constant air as I look for the leak.

 

[nckcalifornia]

If it's leaking that badly you can usually find it immediately by blowing smoke into the tube and see where it comes out.

Careful with this one. Smoking is bad for your health.

Unfortunately no time to mess with it any more today. Other bad news is it looks like the clutch side seal is going to be hard to find. Found one place that has it in a combo pack with the bearing but everywhere else I have looked is out of stock. Any suggestions on where to get parts for these saws? No dealer within 100+ miles from me.

The internet has one I bet and it sounds like you’re a handy guy so be patient and you’ll have her fixed in more time than you think! Then you’ll likely find yourself looking for more. Godspeed.

 

[sevensandeights]

Ok so back at it today. Clutch side is definitely leaking. However, not sure if the bearing is also bad. There is a little play up/down when I wiggle on the crankshaft. More concerning is that the outer bearing race is spinning in the housing and that doesn't seem right.