Dolmar questions (5100S)

[Beardy]

I have a dead 5100S

Probably as the result of ignorance on my part, poor gas, old gas and lack of tuning. I bought it from a big saw dealer online and used it for several years not having been shown how to tune it and not knowing the importance of gas quality, age etc. It finally gave up and seems to have taken out the piston/ring and cylinder. I have been quoted $380 to fix it and advised by the same shop to just replace it.
several questions:
1. Do I rebuild it or replace it?
I like the saw, its light and used to work well. I can't see anything better (lighter/more powerful) without spending a lot of $. Echo CS-600 is available from places like Ebay for similar same money, but seems like its a backwards step in performance (although it has a 5 year warranty). A Dolmar 6400/makita might be the next step, but the $ go up significantly. If I have the 5100S rebuilt, is there a big bore kit that will fit?

2. Is there a recommended Dolmar dealer in SoCal. who can rebuild it and teach me how to keep it in tune?

3. The replacement 5105 has a few changes, so are there any recomended mods or maintenance checks for the 5100S that will keep it reliable long term beyond the obvious of learning how to tune it and not using junk fuel?

Many thanks

Mike

 

[w8ye]

On the 5105 the cooling path was redesigned, there was a catalytic muffler added and the carb needles were set much richer.

On your 5100, a smart rebuilder might be able to save your cylinder and be able to rebuild it with just a new piston and ring?

 

[ncfarmboy]

On the 5105 the cooling path was redesigned, there was a catalytic muffler added and the carb needles were set much richer.

On your 5100, a smart rebuilder might be able to save your cylinder and be able to rebuild it with just a new piston and ring?

Rebuild it we will be glad to help. If cyl is salvageable and it probably is you can clean up alum. transfer w/muratic acid on q-tip and some 400 grit wet & Dry sandpaper. You can replace piston,rings,wrist pin and circlips for $64+ship or piston and cylinder kit for under $200 I think the last one I got was $168 +ship. Ship is flat rate $7.95. Be glad to let you know where. They aren't a site sponsor so PM me if needed. The 5105 and the 5100 use the same P&C it is the big bore. Reliability is in tuning, good premium nonethanol (if possible) and good high quality synthetic mixing oil such as Stihl Ultra and keep it clean. That hurts saying the "S" word since I'm a Husky/Dolmar man but true non the less. There is also an improved air filter for it. With a muffler mod the CS600 Echo should out cut the 5100-5105. And then there is the 6401 you can't go wrong there lots of gitit for the bucks and upgradeable to boot. Great saw. I've got 5-5100's and 2- 6401's upgraded. Be glad to help in any way possible. Advise is FREE parts take MONEY.
God Bless You & Family!
Shep

 

[JustinM]

You've hit the problem that so many people do when they burn a saw.

most dealers (in fact, every dealer I personally know) wont do ANYTHING with a saw that isnt OEM. So that means they will rip yours apart, order a new piston/cylinder etc and put it back together. As you've noticed, this is VERY expensive - nearly as much so as a new saw.

The thing is, if you're handy, there's a very good chance you can fix your saw for less than $100. As w8ye mentioned, there's a fairly good chance you can save your cylinder. This is especially true if you had a quick, catastrophic failure (as opposed to a slower prolonged seize). A fast failure caused by bad gas usually means the piston burns up right away and transfers to the (much stronger) cylinder wall. Some muriatic acid and/or some very fine grit sandpaper & you may find the cylinder is good to go. Then all you need is a piston. To the best of my knowledge there are no aftermarket pistons for this saw. So you'd have to order OEM and should be able to get for around $80 I believe.

If it were me, I would do the following:

1) Strip it down & have a look at the cylinder. Try to clean it up. If it works, Great. If it doesnt, you're only out the time to get to this stage.

2) if it does clean up, then order up an OEM piston & put her back together.

3) if it doesnt clean up then you have a few options: 1) try to sell it (disclosing its got a bad top end). You may still be able to get $100-150+ for it (depending upon the condition) as people love projects. 2) order an oem piston/cylinder. Im not sure how much this will cost you (my guess around $225) and fix it yourself. Expensive, but still not as bad as the original $380 quoted.


As for the 5105 - its got some improvements, but imho they simply make it less likely to fry in inexperienced hands. The cat muffler & other so called "upgrades" actually make the 5105 perform a little weaker than the 5100. Best bet would be a 5100 with the knowledge of how to tune it/keep it tuned.

Good luck.

 

[w8ye]

I have a 5105 and I changed the muffler to a 5100 muffler.

 

[JimmyT]

Beardy, can you post a photo of the cylinder?

 

[Stihl-Pioneer]

I have a 5105 and I changed the muffler to a 5100 muffler.

Me too. Catless of course (the later 5100s had a cat also)

 

[Beardy]

Thanks to all for you advice.

The muriatic acid thing is to remove the aluminum from the steel liner of the cylinder? - assuming that the piston is softer and gets eaten quickly by the acid and the cylinder is harder and wont erode at the same rate?

With regards removing the cylinder I am assuming you can just undo the 4 torx screws and lift the cylinder up off the crankcase?

Can you point me to where I can buy the necessary torx drivers? I have some but they are too thick (too large a diameter shaft) to go through the clearance holes in in the cylinder fins down to the head of the screw. I am assuming this is a bit esoteric for Home Depot to stock...
As soon as its off I will post a a piccy.

Is there any obvious checks I can carry out on the big end while I have the jug off?

Many thanks
Beardy

 

[w8ye]

The hard Eutectic type (Chrome) sprayed inside the cylinder is resistant to the muriatic acid.

Use the acid sparingly as any that gets to places other than the hard coating will eat up the cylinder.

I have bought T-27 long wrenches at Harbor Freight.

There is no reason why HD would not have them

 

[JimmyT]

Thanks to all for you advice.

The muriatic acid thing is to remove the aluminum from the steel liner of the cylinder? - assuming that the piston is softer and gets eaten quickly by the acid and the cylinder is harder and wont erode at the same rate?

With regards removing the cylinder I am assuming you can just undo the 4 torx screws and lift the cylinder up off the crankcase?

Can you point me to where I can buy the necessary torx drivers? I have some but they are too thick (too large a diameter shaft) to go through the clearance holes in in the cylinder fins down to the head of the screw. I am assuming this is a bit esoteric for Home Depot to stock...
As soon as its off I will post a a piccy.

Is there any obvious checks I can carry out on the big end while I have the jug off?

Many thanks
Beardy

Mike, these are the T27 tools that I use: Wiha T27 Bit Socket 1/4" drive 6" long (Wiha # 77160), Matco T27 T-Handle (Matco # THT27), Lisle T27 Torx Bit 1/4" drive. (Lisle # LIS26600) Here is the Wiha website---Wiha TORX Tools Index - Over 1000 Torx Items

 

[grandpatractor]

With regards removing the cylinder I am assuming you can just undo the 4 torx screws and lift the cylinder up off the crankcase?


Is there any obvious checks I can carry out on the big end while I have the jug off?

Many thanks
Beardy

It is nice to pressure check the crankcase before you take of the cylinder. There is threads to show how to do that. I have seen a couple with bad seals.
Otherwise you can remove the carb and intake boot together. There is four screws to remove it. One with the wire under it and one in the bottom of the housing and the other two are obvious. Check the carb boot for tearing or cracks. Then pull the muffler and then the cylinder.
It is easier to remove the carb and intake to get the cylinder off. I usually leave the fuel line hooked up under the housing and just twist it out of the way.

 

[sawinredneck]

I bought a T-27 sqrench from Stihl then ground the handle down to clear the holes in the cylinder. Cheap and effective!

 

[ncfarmboy]

Thanks to all for you advice.

The muriatic acid thing is to remove the aluminum from the steel liner of the cylinder? - assuming that the piston is softer and gets eaten quickly by the acid and the cylinder is harder and wont erode at the same rate?

With regards removing the cylinder I am assuming you can just undo the 4 torx screws and lift the cylinder up off the crankcase?

Can you point me to where I can buy the necessary torx drivers? I have some but they are too thick (too large a diameter shaft) to go through the clearance holes in in the cylinder fins down to the head of the screw. I am assuming this is a bit esoteric for Home Depot to stock...
As soon as its off I will post a a piccy.

Is there any obvious checks I can carry out on the big end while I have the jug off?

Many thanks
Beardy

You can drill the holes out in the cyl. just a little for your T-27 to fit. I have done it before doesn't hurt a thing. I now have proper tool. Note there is a little insert that goes in the intake tube to help with sealing of carb. to tube. This was an upgrade some of the older models did not have it. Look it up @ psep2.biz The PN for the insert is 18113121 $1.00. You can also see PN for the upgraded air filter it's not the nylon one. If you order a piston don't faint when it comes in. The original piston had windows around the wrist pin the new supposedly upgraded piston does not have windows. It is however lighter.

Shep

 

[Beardy]

Thanks to all,

jug is off and I can see several wear marks but the only one I can actually feel is on the exhaust side of the cylinder where I can feel some deposits from the piston. I will try to post a picture when the boss comes home and can operate her camera. Other wear marks cannot be felt. There are some piston ring(?) deposits on the edge of the exhaust port also. I attempt the clean up with acid once I have a picture taken for your review.
If I neglect to replace the gasket at the bottom of the cylinder, I presume this will improve the compression - I have noted the comments made elsewhere on this forum. Is this a good idea and do you have to use some sort of sealant to stop any minor breathing if this is not a perfect seal?

I assume I should replace the fuel filter just as a general maintenance item. Is there anything else I should look at?
thanks
Beardy.

 

[Brian VT]

If I neglect to replace the gasket at the bottom of the cylinder, I presume this will improve the compression

You should check the squish before deciding to not use a gasket. Otherwise, a leak might be the least of your problems.
These saws generally have fairly high compression from the factory anyway.

 

[steve316]

dolmar 5105

I have a 5101 with about 8 to 10 taks of mix ran thru the saw. the compression checked 180 with a new gage from bailey's.With new piston & ring yours should be app. the same. Good Luck in your repair .Steve

 

[Beardy]

The muriatic acid trick is quite impressive and works well. However, the cylinder has some damage below the soft metal deposits. I will order the jug as well and crack on wiith rebuild
thanks

 

[WoodChuck'r]

I have a dead 5100S

You don't say....

 

[ncfarmboy]

The muriatic acid trick is quite impressive and works well. However, the cylinder has some damage below the soft metal deposits. I will order the jug as well and crack on wiith rebuild
thanks

If you go gasketless get a tube of Threebond 1194 or equivlant. Use sparingly making sure you clean surfaces before applying. I use lacquer thinner to wipe down surfaces. I would be interested in the old jug. Don't forget to check psep2.biz web site best prices on Dolmar I've found.
Shep

 

[nmurph]

The muriatic acid trick is quite impressive and works well. However, the cylinder has some damage below the soft metal deposits. I will order the jug as well and crack on wiith rebuild
thanks

Post some pics....a groove below the exhaust usually doesn't affect performance. Only grooves above the exhaust are usually of consequence. They can reduce compression if there are several and they are deep. Even if they are above the exhaust, lots of times you can run it without any side-effects. I wouldn't plop the money down if I didn't need to do so.