Matt_Ellerbee
ArboristSite Operative
No bulb here. I just pulled engine over a few times to get fuel into line and carb. This is a 250-z from the sticker still on it by the dogs.
Re-Assembling Clamshell Engines?
- Thread starter SteveSr
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My MS250 is a frankensaw made by me from several different models and several aftermarket parts. It's not the prettiest saw in the wood but it runs very well.
Matt_Ellerbee
ArboristSite Operative
Well I adjusted carb to factory specs and she fired right up. But the LA screw has no change in idle. Had to run it almost all the way in to even get an idle. Turn saw on side,dies. Recrank on fast idle,turn on side,dies. I think my 515 didn't take,or the crank seals are bad. They are AM. Might pull apart and permatex it. Should I leave AM seals in or get OEM? I don't have a vacuum tester....need to get one.
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Probably be best to get OEM seals since you're having to tear it down.
Chris-PA
Where the Wild Things Are
Hold on, that does not sound like an air leak. Turning the throttle stop in opens the the throttle plate - if you had to turn it all the way in to get an idle there's something quite wrong with the way the carb is set up, but I would not guess lean from an air leak. It may be that the idle outlet is blocked and it won't run until the throttle plate is opened up to the transfer outlets. Or maybe the impulse port is blocked - I can't remember where it is on that engine, so maybe it got blocked by sealant?
cedarshark
Addicted to ArboristSite
I have used Dirko on Stihl clamshells and like it. You can actually get by with a very small bead of sealant using the applicator tip that comes with the tube. Problem with the applicator tip is you waste a bunch filling the tip and have to clean the tip to reuse. I switched to Threebond and have not had a problem. Like Mattyo mentioned above, I do have a problem with the LocTite (I was out of Threebond) sealing a Huskie 450 clamshell but i have not chased the leak down yet.
Get a vacuum/pressure tester. It only takes 1 time having to pull a saw apart again to pay for itself. Block the exhaust and intake. Pressure the saw to approx 7 psi and submerge it in a tub a water. Where you messed up will show up in seconds.
Get a vacuum/pressure tester. It only takes 1 time having to pull a saw apart again to pay for itself. Block the exhaust and intake. Pressure the saw to approx 7 psi and submerge it in a tub a water. Where you messed up will show up in seconds.
SteveSr
Addicted to ArboristSite
I have done some more research and it looks like Threebond 1207B is the equivalent to the Dirko HT Red. The "B" appears to denote high temperature. After a LOT of effort I managed to get PDFs of both the data sheet and MSDS and have attached them for reference.
SteveSr
Addicted to ArboristSite
THe general consensus on this board is to use Stihl OEM seals. I think they may be a special material to better the fuel and heat in these small engines.
To determine if you still have a leak all you need is a bicycle pump, a bucket of water, and a little creativity to seal up the known holes.
New engine 025 is available might need to round upper edge of exhaust to keep ring from catching and do other adjustments to get a bit of use from it
BigRed96
ArboristSite Operative
I have used Motoseal on a couple of MS 290 into 390 conversions and recently used it to seal up an 036 running no base gasket. I pressure test all my saws as well as vacuum test and all have passed.
I use this technique on trouble saws, worke very well!
A blood pressure bulb works pretty well to test with...hook a gauge up to it.
Amp4027
ArboristSite Operative
RTV and any type of sealant will NOT stick to anything that hasn't been sufficiently (read - just evaporated blasted with nonchlorinated brakeparts cleaner).
This thread was a great read: Thanks for the warning and MSDS's about the non-drying sealants listed in this thread guys
This thread was a great read: Thanks for the warning and MSDS's about the non-drying sealants listed in this thread guys
SteveSr
Addicted to ArboristSite
Well, I received t he Dirco HT and had a chance to put the engine back together using spacers. After letting it cure for about a day and a half I performed a pressure and vacuum test and found no leaks. I also noted that the sealant left in the application nozzle also cured within this same time period, unlike the Motoseal which still stayed pretty much liquid.
I also found out why Stihl recommends immediate installation back in the saw after sealing the crankcase. It appears with this clamshell design the bottom part of the clamshell is designed to flex and bend over the bearings and seals. This pressure holds the bearings in place. When I went to install the engine in the plastic housing I loosened the clamshell screws slowly and evenly. In doing this I noticed that the bottom of the clamshell started to open a small gap between the two surfaces. I am assuming that this broke the seal around the edges.
I installed the engine in the housing anyway and tightened everything down. I put a piece of thin duct tape over the intake boot and did a vacuum test. So it appears that I didn't create a new leak by performing the assembly in this order. However, If I was to do another clamshell saw I would probably attempt to immediately put the engine in the main housing. This is a bit challenging to make fit since the intake boot and plastic cylinder shroud has to be installed before the engine can be installed in the main housing.
I also found out why Stihl recommends immediate installation back in the saw after sealing the crankcase. It appears with this clamshell design the bottom part of the clamshell is designed to flex and bend over the bearings and seals. This pressure holds the bearings in place. When I went to install the engine in the plastic housing I loosened the clamshell screws slowly and evenly. In doing this I noticed that the bottom of the clamshell started to open a small gap between the two surfaces. I am assuming that this broke the seal around the edges.
I installed the engine in the housing anyway and tightened everything down. I put a piece of thin duct tape over the intake boot and did a vacuum test. So it appears that I didn't create a new leak by performing the assembly in this order. However, If I was to do another clamshell saw I would probably attempt to immediately put the engine in the main housing. This is a bit challenging to make fit since the intake boot and plastic cylinder shroud has to be installed before the engine can be installed in the main housing.
I've done several of the Stihl clamshell engines and never noticed the engine separating and never had any leaks. I've used Motoseal and Dirko but I let both of them set overnight before installing, it's easier that way.
Chris-PA
Where the Wild Things Are
That's never happened to me on any of the Poulan clamshells I've done using Yamabond4, nor the MS250. Perhaps the Dirco doesn't grip as tight?
Dirko seems to have the consistency of silicone sealer whereas the Motoseal is more like contact cement. Motoseal needs to be applied to both surfaces, let dry a bit then put together. It eventually does get hard.
Interesting read gents....keep it up
SteveSr
Addicted to ArboristSite
Well, I don't think that you can ask *any* sealant to hold under those conditions. It may just be the tolerances of my particular clamshell assembly. It has to be tight enough to hold the bearings securely and any gap has to be filled "forever" by whatever sealant was used. In my case the leak was at the "T" junction of the cases and seal, i.e. where the gap was the widest.
Chris-PA
Where the Wild Things Are
Well, my experience is counter to that. When I take out a clamshell that I have put together or a factory assembly it is often difficult to pry it apart. But I have not used that sealant, and maybe it is a weak adhesive.
The castings those caps are made of is far more brittle than it is flexible. I suspect it is the rubber seals that is pushing it apart - make sure they are properly in the groove.
This project seems to be much more problematic than it should be.
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