Stihl 038 Magnum restoration...continued. Carb rebuild and crank seals.

[Andy171361]

Hello Stihl 038 fans!

Previously I have posted about my Stihl 038 Magnum restoration on threads:

Stihl 038 Oiler on Apr 15 2014 and
Stihl 038 Air Filter - Thank you Willard on Sep 4 2014

At the end of the previous thread I had got my 038 running pretty well and was ready for a bit of milling with my small Alaskan Mill.  All went well initially but two small problems showed up.

1.  The saw would cut really well on full throttle.  I would cut about a foot then leave the saw idling while I moved my wedges and banged them in.  The saw would idle happily but when I went to resume cutting the saw would die as I pressed the trigger.  A good pull on the starter and it would burst into life again and cut happily once more, but I could end up re-starting the saw maybe 6 or 7 times in a 9' log which does not seem quite right to me.

2.  When playing around with the saw (while at idle with the chain brake on, both with and without the Alaskan Mill attached) I found that if I pressed the nose of the bar gently on a log the idling revs would drop.  If I pressed it a bit harder then it would stall altogether.

I suspect that a carb rebuild might solve the first problem and that crank seals might solve the second problem.  But can anybody shed any light on these matters?

Many thanks
Andy



  

[HolmenTree]

Andy, it sounds like your intake manifold has a leak in it. Pulse line from the crankcase to the carb may have a kink in it too.

[Andy171361]

Hello again Willard!  How nice to hear from you and thanks again for all your help with my earlier threads.

I had previously been put off a carb rebuild as the Stihl kit here in England was going to cost about £40 (US $60).  I have since sourced a kit for a fraction of that (£8 which includes postage from the USA).  The kit is made by Tillotson and the quality seems decent.




 

As you can see, there was some muck under the pump diaphragm.  Also the pump diaphragm itself has lost its shape a little.  I have had the saw running since the carb rebuild but I have not tried milling with it yet.


  



 

The metering diaphragm also looks a bit past its best, so I hope that my carb rebuild may have helped in respect of the first problem - ie stalling when I hit the trigger.



 

I replaced the impulse line earlier this year.  I tried hard not to kink it but that does not mean that I succeeded.  I will have a look at that next time that I take the saw to pieces.

As for the manifold, I replaced the piston earlier this year and while the saw was in pieces I had a really good look at the manifold.  The rubber seemed to be in pretty good condition and there were no obvious holes in it.  One thought about that though.  When I replaced the cylinder I used the official red Stihl sealant at the manifold/cylinder joint.  Then (and I can't remember why) I had got it slightly wrong so I had to uncouple the manifold from the cylinder.  The second time I attached it I did not use the sealant as I found a contradictory reference saying that the sealant was not necessary.  So Willard, where do you stand on the use of red sealant?

Anyway thanks, as ever , for your help.  It is always much appreciated.

Andy

[HolmenTree]

I've never had to use the sealant, just a good pliable rubber manifold and a clamp with not too many years on them should be all you need. When you used the sealant the first time and not the second time maybe there is a poor seal with the old sealant possibly still in the joint. As you mention earlier about pressure put on the bar nose effects the running condition of the saw, I'm thinking leak at the intake manifold.

Look like some beaded corrosion in you carb, possibly old decayed fuel mix.. Takes a bit talent and patience to clean the carb out completely.
You may have saved money and time with just a purchase of a new carb, which what I have done at times.

[Andy171361]

That's a good point about the possibility of not having removed all of the red sealant when I re-fitted the manifold the second time.  I'll have a look at that over the weekend.

I had not even spotted the pitting you mentioned.  You certainly have eagle eyes!  I am pleased to have rebuilt the carb.  If I end up buying a new one then so be it.  But in the meantime I am enjoying expanding my knowledge of chainsaws as I plod along.  It also helps me to understand all the information in the various postings if I have at least tried to do a job.

Anyway thanks again for the suggestions.  I will have a close look at the pulse line and manifold joints and report back in due course.

[Andy171361]

 

 

Hello Willard.  Here is an update on my 038.  You were quite right, of course! 

The pick up from idle is certainly better since the carb rebuild so next I removed the carb again and had a look at the manifold.  I went to tighten the clamp and it was immediately obvious that the manifold had spilt beneath the clamp.  Well it certainly was not this bad 6 months ago when I replaced the piston!  Anyway, I have no doubt that this was the cause of the idle revs decaying when the nose of the bar was pressed down, so thank you for the suggestion.

I have ordered a new part and I will let you know how the saw is once it has been fitted.

Thanks again

Andy

[HolmenTree]

Hey Andy ,  I'm happy I was able to help you. Yes I remember some  of my 038 manifolds split the exact same way just under the clamp.
Rubber definitely degrades, especially bad when it's 30 years old.

[Andy171361]

Hi Willard.  That's interesting about the manifold often tearing beneath the clamp.  It also makes the fault harder to spot, as one minute the saw is working fine and the next minute it is not quite right.  Plus just looking at it with a torch makes it impossible to see the tear, as it is covered by the clamp.  A bit like a dry joint in electronics.  I have ordered a new part so hopefully I will have the saw running again soon.

[Andy171361]

I have now fitted the new manifold and I am pleased to report that the saw runs very well.  The two snags I had at the start of this thread are certainly solved.

What I would say is that the carb rebuild was actually much easier than I anticipated and it is the first chainsaw carb I have rebuilt.  I would certainly recommend "having a go" to anybody thinking about doing it.  All you need is a nice clean kitchen table, some nice clean tools, a carb kit and an absent wife for a couple of hours!  (Which should give you long enough to get the smell of petrol out of the kitchen before she comes home, once you have completed the job!)

Thanks again to Willard for the pointers.

Andy

[sawguy21]

 :D I wondered if you are married when you mentioned the kitchen table.

[HolmenTree]

I'm glad  it all worked out for you Andy
Now go out and enjoy that saw 8)

[Andy171361]

Hello Sawguy

Actually I can't complain.  As wives go mine is a bit of a smasher!  My other hobby is a 1967 MGB car.  A few years ago I decided that the obvious way to wash the cylinder head before sending it away for a rebuild was by sticking it in the dishwasher.  Well, I waited for my wife to be away for long enough to get the job done and washed it on the hottest setting.  The result was great.  But I had not reckoned on the thin film of engine oil that completely coated the inside of the dishwasher... for days!  And my wife was completely unfazed by it.  You couldn't make it up...

Willard

I fully intend to enjoy using my trusty 038, so thanks once again and a very Happy Christmas to you.

Best wishes

Andy

[HolmenTree]

Andy , have a Merry Christmas  and a happy new year to you too :new_year: