Makita Dolmar 6421 problem

[Highbeam]

Was having a great day just finishing bucking up 5 cords of fir logs. Only found one metal object and everything was working perfectly as usual with this ex home depot saw that I bought several years ago.

I noticed a nice noise change. It got louder, more raspy. I could see some looseness on the muffler and some oil tar leakage. Stopped. Pulled out the little star shaped hole guards and found one of the two muffler bolts loose and the other completely fell out of the threads. The screw looked fine so I tried to put it back in but it just spun as though the threads are gone. The screw had no aluminum in the threads, they looked clean. With one tight screw I finished the last log and set it down to cool. Now I am missing the one screw that was working. It must have fallen out during that last log.

Do Dolmar muffler screws have a habit of stripping out the head? This saw is an ex home depot rental but appears to have never been opened, it was in great shape when I got it. Those muffler screws were factory tightened.

If those screw holes are all stripped out is this something that can be repaired or is it time for a new P&C?

Here’s a photo I took just before noticing.

 

[EbS-P]

Is there enough metal to drill it out and tap it a size bigger? I had my muffler get loose by the time I stopped (finished milling a wide 11’ cut ) the ears with the holes on the muffler were broken out.

Loctite the new screw

 

[Highbeam]

Is there enough metal to drill it out and tap it a size bigger? I had my muffler get loose by the time I stopped (finished milling a wide 11’ cut ) the ears with the holes on the muffler were broken out.

Loctite the new screw

I'll pull the muffler and check. The dang cat muffler was smoking hot after bucking that 14' log. I need to clean it and then tear the bar off and the left side dawg before complete muffler removal.

An aftermarket 85cc top end is about 100$. OEM is about 300$. A new chinese 372xp or MS660 is 300$. I paid 275$ for the dolmar about 10 years ago.

It's too bad, I really like this dolmar and hopefully it can be saved.

 

[qwee]

I have this saw and have rattled those screws out, too. Loctite on reassembly is a must. Unclear is the screw stripped or are the threads in the cylinder head stripped? Don't scrimp on replacement screws - they might look right but they'll lead to problems (tell me how I know this).

I had to have someone helicoil an insert into the head in order to get new threads. It has worked fine. I bought a Hyway cylinder kit to bump my saw up to 79 cc but found a good deal on a new Makita 7900 ($650). Today was my first usage of this saw - I warm to new saws slowly - and you can be sure I'll be checking the muffler's tightness quite often.

 

[Highbeam]

I have this saw and have rattled those screws out, too. Loctite on reassembly is a must. Unclear is the screw stripped or are the threads in the cylinder head stripped? Don't scrimp on replacement screws - they might look right but they'll lead to problems (tell me how I know this).

I had to have someone helicoil an insert into the head in order to get new threads. It has worked fine. I bought a Hyway cylinder kit to bump my saw up to 79 cc but found a good deal on a new Makita 7900 ($650). Today was my first usage of this saw - I warm to new saws slowly - and you can be sure I'll be checking the muffler's tightness quite often.

The one screw that rattled loose has perfect threads but wouldn’t screw back in. Best case scenario is the head threads are fine and things just rattled apart. I’ll gladly buy two new 1.87$ screws and use loctite! Worst case is completely missing head threads. Might as well try a helicoil at that point.

Hopefully tomorrow I can disassemble to investigate.

 

[TomMcDonald]

Helicoil or Timesert with red loctite will make light work of stripped aluminium threads.

 

[Jags]

If there is enough meat left for a helicoil then drilling and tapping is also an option. Loctite for sure with either solution

 

[salecker]

I'll pull the muffler and check. The dang cat muffler was smoking hot after bucking that 14' log. I need to clean it and then tear the bar off and the left side dawg before complete muffler removal.

An aftermarket 85cc top end is about 100$. OEM is about 300$. A new chinese 372xp or MS660 is 300$. I paid 275$ for the dolmar about 10 years ago.

It's too bad, I really like this dolmar and hopefully it can be saved.

While you have everything apart it would be a good time to gut the muffler for the good of the saw.
Then retune for the free flowing exhaust

 

[Highbeam]

I have this saw and have rattled those screws out, too. Loctite on reassembly is a must. Unclear is the screw stripped or are the threads in the cylinder head stripped? Don't scrimp on replacement screws - they might look right but they'll lead to problems (tell me how I know this).

I had to have someone helicoil an insert into the head in order to get new threads. It has worked fine. I bought a Hyway cylinder kit to bump my saw up to 79 cc but found a good deal on a new Makita 7900 ($650). Today was my first usage of this saw - I warm to new saws slowly - and you can be sure I'll be checking the muffler's tightness quite often.

So I got it apart and things look pretty good actually. The old screw that rattled out will not go back in, I believe the screw threads are rounded or somehow no good anymore since another case screw will thread right in. I cleaned everything and the head threads look as good as any. The piston and cylinder also look as good as new with no scratches or anything. Phew.

I'll need a new port gasket and two new muffler screws. Does anybody have a preferred parts source for these cheap parts on a dolmar?

I have the cat muffler in my hand and in priniciple I would like to modify it all to be efficient and durable but the dang saw works just fine all EPA smog compliant and the P&C seem to be holding up fine. I use the fancy echo oil for premix. I don't even have the carb limit caps removed.

So anybody have a good saw shop to buy these parts from? As you can imagine, out west, the saw shops around are mostly all Stihl.

 

[Highbeam]

One more question... loctite for these screws? What type of loctite?

 

[ericm979]

Regular #242 (the common blue stuff) is probably fine. Torque it to the spec in the manual.

 

[Highbeam]

Regular #242 (the common blue stuff) is probably fine. Torque it to the spec in the manual.

It probably gets hotter than heck here at the exhaust port.

I'm not a fan of torque specs when it comes to fasteners this small and with lubed threads. I have an inch lb wrench but think I'll just get it good and tight.

 

[Jags]

Red 272 is for high temp applications. But do keep in mind that it makes a darned near permanent install of those screws.

 

[salecker]

If it's metric,which i am sure it is.
Get the replacement screws from Stihl.
They have serrations on the bottom of the heads and will hold better that the rest.May not need loctite for them.
You can buy sheets of exhaust gasket material at NAPA and cut your own,I just cut a gasket for a 2005 Blazer from my sheet yesterday.

 

[Highbeam]

Thanks folks. I ordered from Jack's small engines. OEM parts. I have some blue loctite to use. Will follow up when it's all back together and running.