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Project TS420 Concrete Saw

Discussion in 'Shop Projects' started by Automender, Jan 12, 2022 at 10:02 PM.

  1. Automender

    Automender OPE Member

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    I picked up a Stihl TS420 saw for $50 and wanted to try to refurbish it. This is my first time to completely rebuild a saw. I have installed new rings in a Husky K970 cutoff saw and rebuilding the carb. I have no history on this saw nor why it failed other than the person said it was a top end issue. I decided to strip the saw down the other day and found two thing I could use some advice on. On the strip down I found play in the crank bearings and what looks like pieces of bearing cages in the crankcase. So those need to be replaced but the rod bearings do not have any play up or down and back and forth. The rod however rocks side to side and I am not talking the normal sliding side to side. I am thinking this needs to be replace due to the rocking motion but wonder why no vertical play.
    Second issue is that the piston looks pretty good and likewise the cylinder looks good compared to You tube videos on failed saws. However the piston top looks like it has some erosion on the top. What causes this type of damage?
     

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  2. Automender

    Automender OPE Member

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    Ended up going to HL supply around Christmas while visiting my daughter in Florida. Picked up a crank and bearings along with a carb kit. I bought a Cross Performance cylinder and piston with rebuild kit during a sale in July.
    I spent hours cleaning up concrete dust on the crankcase and stripping it down. I decided to install both bearings on the new crankshaft before putting the case halves together. I put the crank in the deep freeze for a few hours to get it to -5 degrees and heated the inner bearing races to 300 degrees per service manual. Both bearings just dropped into place with no resistance at all. I then placed the crank and bearings in the deep freeze for an hour.
    I heated the bearing area of the case halves with a heat gun and the cold bearing just slid into place. I installed the case gasket that I coated with Motoseal on both sides on the one half and heated the other case halve bearing area. Case halves slide together without any force and then ran the case bolts in. I was happy to get that done, first time working on a case.
    I oiled the bearings with two cycle oil using a syringe and oiled the shafts.
    I made a install sleeve from thin plastic from a notebook page protector. Rolled it into a tube and slid it into the seal. Slid the sleeve and seal on the shaft, coated the seal with a dab of Motoseal and positioned it to press in. I used a 19mm deep well socket for the one side and a 17mm on the small seal. A few taps and the installed easy. Next I need to check the cylinder port chamfers on the Cross Performance Cylinder kit. Any tips on my next step on the cylinder install would be greatly welcomed.
     

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  3. Automender

    Automender OPE Member

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    Looked at the aftermarket cylinder port chamfering and in general it looked decent to an untrained eye. There were a two transfer ports that seemed sharp so I decided to use a diamond file to ease the edge and then 400 grit wet/dry paper to smooth the chamfer even more. All feel smooth to the finger running over them in any direction. Diamond file fit perfectly in the port to ease both top and bottom edges at once. I think my next step is to measure squish in four different locations. Does any one know the minimum squish for Stihl saws. I am not looking for super just normal performance and reliability.
     

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  4. Automender

    Automender OPE Member

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    Is there any advice on what I should do for the piston wrist pin clips? I have read a few articles on these clips which say never use a clip that isn't supplied with the piston. It is obvious that the AM clip is thicker than the OEM. Also that the clips if supplied with an "ear" you should cut it off. I suspect I would use a Dremel tool with a wafer wheel and keep it cool so it doesn't lose it's heat treatment.
     

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  5. Automender

    Automender OPE Member

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    I decided to measure the depth of the squish bad on my OEM cylinder and then the Cross Performance one. I was hoping they were the same or maybe because the word performance is in the brand name that aftermarket one maybe a little shorter. The distance form the gasket surface to the squish ring on the OEM is 2.827 inches and the aftermarket is 2.847 inches. So I start out with .020 inches more squish. Using the old cylinder gasket I get squish in three locations of .0600, .0605 and .0595 inches. It looks like the original OEM squish was in the area of .038 inches by using data gathered.
    I measured the aftermarket gasket to find that it is .0345 inches so if I used the new AF gasket with the AF cylinder I will have .0725 inch squish which I would give an uneducated guess is way too much. If I do a full gasket delete I will end up with .040, .044, .040. Not exactly to happy with the Cross Performance performance at this point but without a gasket at least I can get back to OEM squish.

    Is it a good idea just to use Motoseal and no gasket at all or do I go with a thin gasket and have .040 squish? Or maybe just go with .060 to .070 squish?
     

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    Last edited: Jan 14, 2022 at 6:05 PM
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  6. Shane¹

    Shane¹ Super OPE Member

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    I don't work on many Stihls or cutoff saws but I see you haven't got any responses i would say use the clips that came with the kit. Trim the ears off with a cutoff wheel. Use a sealer and run the cross cylinder with no gasket. I don't think you would notice any power difference especially with a cutoff saw and you said in an earlier post that you just want stock performance from it.
     
  7. Automender

    Automender OPE Member

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    Thank you for the response. This is my first full rebuild and although I have read all the articles that I can, I need some real life input. OEM parts would make it easier but for a learning experience I can't justify it. I think I will delete the gasket and trim the ears off as you suggested.
     
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  8. Shane¹

    Shane¹ Super OPE Member

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    Oem is for the most part better but I have rebuilt several saws with aftermarket parts and never had any real issues. I think most aftermarket stuff gets a bad rep because it's not put together right or the cause for the original failure was never found. Make sure there is no sharp edges in the cylinder, set the end gap on the rings and put it together and I am sure you will have a good runner. Saw looks good by the way looks like you are making good progress
     
  9. Automender

    Automender OPE Member

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    This saw was scraped because of what looks like semi stripped sparkplug threads and leakage at the plug that melted a small hole through the plastic cylinder cover. On disassembly I found a bad cage in the one bearing but cylinder surface and piston was good. Other than the squish issue the cylinder quality was really good with good chamfers on all ports with just a slight touch on two of the transfer ports. I have a Mighty Mite to pressure/Vac test it after I get the cylinder mounted. I plan on using inner tube, backing plates and a C clamp to seal it while using the impulse tube for the test connection. Learning a lot about two cycle engines.

    I'll check the ring gap which I didn't think about once I pull the cylinder. I did that on a K970 Husky that I just put in new rings to increase pressure. Rings were really worn.

    IMG_4012.jpg IMG_4219.jpg
     
    Last edited: Jan 15, 2022 at 10:34 AM
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  10. Shane¹

    Shane¹ Super OPE Member

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    Sounds like you are well on your way to having it done
     
  11. qurotro

    qurotro Cookie Cutter

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    Bad gas for the piston damage.
     
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  12. Automender

    Automender OPE Member

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    I guess I just couldn't do a total base gasket delete or maybe just wanted to try to make a base gasket. I used an aluminum soda can and sanded all the coatings off both sides with a random orbit sander. Used a base gasket as template and scored it with an razor blade but used an Exactor blade to puncture outline of the screw holes. I bet a paper hole punch would have work good. I flexed along the score lines to break the waste away. Reamed holes to perfect size with a roll of sand paper I finally place 220 grit wet/dry paper on a flat surface and sandwiched it between another one and lapped flat. It ended up being approximately .004 plus a thin layer of Motoseal on both sides. I guess final squish will be .043 vs OEM of .038.
     

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