Dolmar 341 first build

[Herto]

This is my first proper build, I've done a couple of drill through the muffler type muff mods and a fair bit of saw tuning and repair.

Bought this 341 for £20, wouldn't run.
Bad fuel line. Snipped the bad bit out and bodged it back together.
It ran well then.

Next, muff mod.
I'll let the pics do the talking.

But cuts much better, quicker acceleration, more torque and holding higher rpms in the cut. I needed to lean on it to stop it four stroking.

I'll order some fuel line, pull the jug and do what I can to lightly improve supply. I want this to be a good general runner and not fussy.

Squish .031, hoping to drop it to .017-.020ish
More to come

Sparkplug mid cut, spalted beech and infected cookies.
Merry Christmas!

 

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Squish without the base gasket seems to be .014 one side and .015-16 on the other.
I think I'm going to machine a slight pop up on the piston to match a .005 step around the outer edge of the squish band.
Maybe up to .005 tall by .1-.15 in from the edge.

Thoughts? Find some paper to make an .003 gasket? Or machine a slight pop up?

I realised this thread is in the wrong place. Should be in modded work saws or just chainsaws.

 

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I opted for the pop up, less work in the short term.
I should have measured piston height to get an accurate pop up but I just winged it.
I'll put it back together and check squish again later or boxing day.

Any reason to keep the inlet and exhaust ports narrower than 2mm less than piston skirt?
I think I'll hardly touch the transfers. Soften a couple of edges and slope the top of the inlet side transfers a bit more

 

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So I've been AWOL as things have been busy, I made some terrible mistakes, and I've been waiting for parts.
So I'll continue the post, warts and all.

 

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Here are some pictures of the progress.
Like I say bad bad job.
The intake tract was incredibly choked down, and included a "ream between the lines" mark.
Here's my intake and exhaust ports, and the intake tract and the repairs I did, as a result of bad freehand work with a drill and drill bit.

 

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More pics
I redrilled the impulse hole in the tract where I repaired it. Although this saw pulse from the cylinder via a pipe, everything is there to pulse it through the block

 

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Here's where I lost my mind working in the cylinder with a chainsaw file.
For me the takeaways are,
#1 leave the transfers alone
#2 work within the limits of your tooling.
#3 remember and take seriously advice you read on porting threads

I'm going to get some better equipment for my next build.

Luckily my friend offered to tig up my mistakes on the transfers.

A bench I made in the meantime

 

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I bought a new caber piston ring (do they always say caber on the ring?) As I snapped the old one.
Squish .014/.015 "gulp"
Couldn't be bothered to machine more or make a gasket. I'll watch for head banging witness marks on the piston.

Set it up rich and idled it a couple of times, then gently broke it in rich.

Finally breaking in for the video, but still not "turned up" all the way

 

[Sidecarflip]

I just picked up an old Dolmar that runs but the warmer it gets, the less power it makes. I suspect the rings have lost their tension. Have not taken it apart yet, I'm curious to see how bad it is....

 

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Judging by the pull start test, compression may be down, I'm not surprised with poor seal over the welds, but performance is up, the saw seems to be less allergic to dogs.

I think the last thing I'll do is rebore the carb.

 

[Herto]

I just picked up an old Dolmar that runs but the warmer it gets, the less power it makes. I suspect the rings have lost their tension. Have not taken it apart yet, I'm curious to see how bad it is....

What model is your dolmar?
If you search on here you'll find help measuring ring gap, which indicates wear.
If it's newish like mine, it may be very restricted in intake and exhaust. You might run it cooler with some mods.

But most importantly getting the carb adjusted right.

 

[Herto]

I just picked up an old Dolmar that runs but the warmer it gets, the less power it makes. I suspect the rings have lost their tension. Have not taken it apart yet, I'm curious to see how bad it is....

Sometimes your piston ring is stuck in the piston and not free to move to create a good seal.
You could inspect this through the exhaust port,

 

[Sidecarflip]

Not that far along. Just got it the other day actually. I need to pull the muffler off and have a 'look-see' first thing I suspect. It has a ton of hours on it so I'm anticipating the worst. The AF was totally plugged up when I brought it home and cleaning it made no difference. Starts good, runs well but as it warms up, it gets worse and worse which leads me to suspect the rings have lost their tension or worse.

The owner is still the owner, not me actually. I was given it to see what is up with it. First thing I need to do is clean it up, it's totally filthy. Have a feeling it's all carboned up anyway. The owner always ran Stihl pre mix in it.

 

[Herto]

Not that far along. Just got it the other day actually. I need to pull the muffler off and have a 'look-see' first thing I suspect. It has a ton of hours on it so I'm anticipating the worst. The AF was totally plugged up when I brought it home and cleaning it made no difference. Starts good, runs well but as it warms up, it gets worse and worse which leads me to suspect the rings have lost their tension or worse.

The owner is still the owner, not me actually. I was given it to see what is up with it. First thing I need to do is clean it up, it's totally filthy. Have a feeling it's all carboned up anyway. The owner always ran Stihl pre mix in it.

Sounds like a good project. Pics?
+1 to pull the muffler first.
Read lots on here, use a bright light and look for piston, ring, cylinder wear. Push the ring carefully with a screwdriver to see that it's free in the piston

If can run, has been tuned right, had premix and it's carboned up, then it's probably not worst case. Running rich will rarely cause damage, but get a better and more experienced opinion than mine. Good luck!

 

[Sidecarflip]

Knowing who owns it, I'm sure it has excessive hours on it. It's old and now tired but I need to take the muffler off at least and see how it looks inside. I have other more pressing issues right now as in hooking up my TIG water cooler to my new water cooled CK 250 amp TIG torch. Already a 'plumbers' nightmare plus it's cold and snowing here, least it's warm in the shop.

 

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Knowing who owns it, I'm sure it has excessive hours on it. It's old and now tired but I need to take the muffler off at least and see how it looks inside. I have other more pressing issues right now as in hooking up my TIG water cooler to my new water cooled CK 250 amp TIG torch. Already a 'plumbers' nightmare plus it's cold and snowing here, least it's warm in the shop.

I don't envy your plumbing, but I'm sure you're excited to have your new Tig set up.
No snow here, but certainly freezing.
I'm off to do some more cutting, and see if this saw wants to be turned up all the way

 

[Sidecarflip]

Not gonna modify it in any way if I don't have to actually. I just need to ascertain why, as it warms up, it becomes a slug saw. Thinking a new piston and ring set is in order if anything and probably a pressure test to see if the crank seals are shot. it's been run on e-gas all it's life so the fuel and pulse lines are probably shot as well.

I'll have a good idea when I take off the muffler and look inside with my Gradient Lens Hawkeye borescope. Like I said, I suspect the rings have lost their tension. I will have to source parts however. Not at all familiar with Dolmar saws in the first place. It's kind of an 'odd' looking saw, not something I'm familiar with. Will find out when I get time. I need to play 'plumber' presently with my new TIG torch. More pressing as I have a CNC plasma cut job cut that needs to be TIG welded and it's aluminum. Customer is anxious, like all customers are today. It certainly needs a new air filter as well as the one that is on the saw has seen it's useful life come to an end.

 

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Not gonna modify it in any way if I don't have to actually. I just need to ascertain why, as it warms up, it becomes a slug saw. Thinking a new piston and ring set is in order if anything and probably a pressure test to see if the crank seals are shot. it's been run on e-gas all it's life so the fuel and pulse lines are probably shot as well.

Sounds like you know where to look, old fuel lines are a first check for me, It could be an air leak that shows up after the saws warm.
I'm keen to see pics or a model number when you get to it

 

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Here's my rough effort to record final timing numbers, please correct any mistakes you notice

Ex open 101
Duration 158
Transfers open 125
Blowdown 24
Intake open 72
Duration 144


My " timing wheel"

Exhaust open


Transfers open


Exhaust close


Intake open


Intake closed

 

[Sidecarflip]

I'll get around to that. I have other 'stuff' that is more important presently. Besides, it's snowing and cold here. Not a day to be fiddling in the shop even though it is heated.