stihl ts420's and husqvarna k760's and k750 total rebuilds. best parts to use for $ other than OEM?

[ginsenger]

If they want me fixing these saws, on nights and weekends, after doing a youngs mans job all day, and me 60, (on days of working with 12 inch block most of them young guys are wore out), They are going to buy me new parts and tools to do a good job.. lol

 

[alexcagle]

The carb seals diectly against the boots that are seated into the three bolt aluminum intake flange.
The intake gasket between the tank and carb is the only gasket.
They are in a new gasket set, even aftermarket sets.
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If you reuse the crankcase gasket at the split, just push up slightly right before the gap closes tight. Then cut it off flat at the deck with a razor. If you do reuse them, you need sealer. They will leak with vibration between the longer stretch between the two bottom bolts. Something gasoline resistant like Yamabond 4, hondabond, 3bond. Silicone will leak.
A minor case leak becomes more pronounced as the saw gets hot, and makes the saw lose power.
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Make sure you put a slight wedge between the crank counterweights when you pull the halves together with screws, so you don't bend the crank.
The bearing pockets and outer surface need to be oil free when put together or you'll see the bearing pockets waller out after a while. Lacquer thinner works great on a paper towel. A drop of green loctite "press fit" bearing retaining compound is a good idea too.

 

[alexcagle]

I use a very fine wet stone for sharpening knives and give the gasket surfaces a light decking. They are all pulled around the bolt holes. not much but a little. I stop decking just before All the color of old gasket is gone and then finish with scotch brite pad by hand.

There is only one bolt thread that doesn't have a dowel on the crankcase split on a TS420, and the cylinder base threads are in the cylinder itself..... what pulled threads are you referring to?

 

[ginsenger]

The pulled boles are the ones in the block to pull down the head (jug) , and the block halves draw together bolts. actually so far I just have done the k760s. the place I ordered the bearings from gave me all one size so I just went to working on the huskies and haven't got back to the stihls yet. It is probably only a thousandth or so, maybe less, but they clean off first at the holes every time when I deck them. I pull the dowels out first. The stone is a super fine whetstone in new condition,it won't take off much very fast. but it covers me for the block having been hit or banged up or warped. I bought a set of these pullers in the photo and another set for putting the bearings in the case, to keep from hitting bearings or bending cranks as you say. I have a small lathe and made a seal driver, lol out a small aluminum flashlight that was already close to the right size. I already had pullers that it takes to get the bearings off the crank. I have a heat gun already. I had to weld the metric bolts on to 3/8th bolts to get the right length for the puller for the k760 with out spending on them too. I got metal to make the block splitter and got a templet from on here to make it for the stihls. But I am going to try to modify it to fasten each half the puller to a flat slotted snap-on puller bar. I would be adjustable to fit different widths then..I will have to get the blue loctite, all i got is red.. On the trucks and such I used to work on we went to the aerobic gasket eliminator instead of silicone. too much of the silicone goes inside and plugs up oil and water holes. I don't use it much. But I will check out the yamabond you suggest (thanks, I never heard of it before) . I try not to use old gaskets, the company got the money and I like to do a good clean job. but I haven't been throwing them away either.

 

[ginsenger]

GREEN loctite I don't have either.

 

[alexcagle]

Sounds like you're getting it figured out.
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You might think about getting some extra long 5mm helicoils 2D and 3D to repair exhaust flange and cylinder base threads. Schinese make a good cheap 5m thru 22m helicoil kit on ebay for around$35- $40 that is great for repairing cutoff saws.

 

[ginsenger]

I got the 5mm helicoil drill, tap, and install tool. got all kind of sizes for other stuff too. How long a thread insert should I get for the saws??? Fastenal had some different sizes but wish they had longer ones.......exhaust on stihl mostly and starter housings on the k760 so far.

 

[ginsenger]

one of the stihls I did the exhaust on did not hold . I thought of using a tiny wire to put in the hole to help lock it down. I have done that on stripped holes in aluminum without a helicoil. but what do you know about it other than long helicoils. It is near imposiable to double them up as the threads wont line up and match. At least I haven't had much luck at that in the past on bigger stuff.

 

[ginsenger]

Made this little piece to cap the exhaust on k760 tonight, some billet aluminum I had laying around, was just the right width got in a hurry and didnt centerpunch the boltholls so one is a tiny bit off. no big deal, just a few thousands. still got to get something rigged for the intake side.,,, How can I tell whats wrong if the block holds preasure.

 

[alexcagle]

Made this little piece to cap the exhaust on k760 tonight, some billet aluminum I had laying around, was just the right width got in a hurry and didnt centerpunch the boltholls so one is a tiny bit off. no big deal, just a few thousands. still got to get something rigged for the intake side.,,, How can I tell whats wrong if the block holds preasure.
View attachment 566870

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What exactly do you mean by the question in the last line?
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These vacuum & pressure testing techniques may help.

 

[alexcagle]

In reference to the muffler threads problems, here is an old thread I made on the issue.
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http://www.arboristsite.com/community/threads/ts420-muffler-hack.299522/
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The longer helicoils can be obtained on ebay by searching:
either 5m 2D helicoil
or 5m 3D helicoil
The 2d equates to length being 2 times the dimentional diameter. etc..

 

[ginsenger]

What exactly do you mean by the question in the last line?I mean that I tore down several saws,that had burnt pistons without preasure testing them before I tore them down. Now after I totally rebuild them and if they pass a vac. and pressure test, What do I need to double check to make sure their right. If I give a saw back, they will run it into the ground before they quit. If it can be made to start and run they will make it go no mater what it does. I can't be there to keep an eye on each and every saw. So how or what do I do to make sure its right when done.

 

[ginsenger]

In reference to the muffler threads problems, here is an old thread I made on the issue.
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http://www.arboristsite.com/community/threads/ts420-muffler-hack.299522/
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The longer helicoils can be obtained on ebay by searching:
either 5m 2D helicoil
or 5m 3D helicoil
The 2d equates to length being 2 times the dimentional diameter. etc..

Thanks Alex

 

[alexcagle]

Just recheck for leaks with soapy water to isolate a leak.
Things that can burn up a piston.....
Check tank vent operation.
Operator vest (clothing) sucking and blocking off cooling airflow on starter.
Partially clogged carb screen.
Restricted fuel filter.
Collapsing fuel pickup hose.
Water in fuel.
Diesel mixed with gasoline.
Boat 2-stroke oil.
Stale old fuel (detonation).
Low octane fuel.
Impulse hose pinhole.
Wrong heat spark plug.
Plugged cooling fins.
Intake leak.
Crank bearing seal leak.
Dirt or dust passing the air filter.
Incorrectly adjusted carburetor.(lean)

 

[ginsenger]

Alex, my supposed leak under my home-made intake seal for testing the k760 was not the intake rubber, it was the jug gasket right under that. I found some hondabond 4, pulled the jug and put a thin sticky coating on each side. used green loctite on jug bolts.... It lost (1) pound of pressure in 5 or 10 min, I think that was from spark plug as I sprayed the soapy water on everything and all seemed good. It seemed to have sealed better after turning it in and out a bunch of times, and sitting a few days. I may still put a tiny bit of red hightemp on the spark plug seal before finishing.
??
I didn't put honda bond on crankcase half gasket. Should I leave it as is or what at this point??
??
Should I pull the crank case bolts one at a time and put loctite on them.??
?
If I take carb apart to check the screen should I use new gaskets or, put a kit in it,, Or is there a test to check all that without taking it apart.?

 

[alexcagle]

That leak is acceptable.
What about vacuum testing?
How did you put the crankcase together.
Heat, or long bolts to pull it together?
You don't need loctite on the spark plug, or the crankcase split gaskets.
You won't need to replace the carb gaskets, but you need to check for contamination, and put back together clean, then test it.

 

[ginsenger]

That leak is acceptable.
What about vacuum testing?
How did you put the crankcase together.
Heat, or long bolts to pull it together?
You don't need loctite on the spark plug, or the crankcase split gaskets.
You won't need to replace the carb gaskets, but you need to check for contamination, and put back together clean, then test it.

I heated the housings and put the bearings, (froze bearings in freezer), pulled in with a threaded puller I bought for that and then used another threaded puller to pull the crank into the halves. used the modified flashlight to install the seals below the block surface. I forget now how many thousandths but I found the depth somewhere and made it as it was called for. when the outside of the driver hits the block the seal is maybe 4 mm below the surface.

The carb,,, I went ahead and took it off and used a new gasket....I used gas and a brush and air pressure to clean the whole carb at first then brake clean to clean inside, while holding the butterflies open, and then the whole thing again.

A while back I fixed another one that the concrete dust had built up on the side of carbs so bad the butterflies wouldn't open up and wouldnt start. cleaned it and lubed the shafts and kept working it till it moved freely and they are still using it so far.

 

[alexcagle]

I was taught that carb cleaners and compressed air are potential check valve killers. The caustic carb cleaner can distort the rubber disc, and high pressure can break the mylar ones.
I was also taught the best flush and internal cleaner is a lubricant like WD40, as it is clean and it wets the tiny check valves.
I use lacquer thinner when finished on the carb's exterior to remove the oily residue to keep the dust from sticking to it.

 

[alexcagle]

I'm a little unclear on what your seal depth should be, but it should be flush with with the case. If you drive them below deck too far it will eat up the bearing from contact.

 

[ginsenger]

Replacing the seal on the flywheel side Mod. 500, 540Mod. 650, 700 Dismantle all parts on the flywheel side so that the seal is accessible. Remove the draw key for the flywheel by means of diagonal cutting pliers. Screw down the seal extractor as far as possible in the seal and pull off the seal. Lubricate the shaft with a few drops of oil and place a new seal in position with the shell plate facing outwards. Press down the seal with a suitable drift to the correct position in the crankcase, 1 mm (.04") below the crankcase plane. Fit the other parts in the reverse order to dismantling.

this is from Partner_Workshop_manual.pdf