Re-Assembling Clamshell Engines?

[SteveSr]

Hello,

This is my first foray into into clamshell seal replacement on a Stihl 1123 (025). The seals are on order and should be here by the end of the week or early next.

The Stihl service manual indicates to apply the sealant and then immediately put the crankcase assembly into the main housing and torque down.

Having never done one and knowing the twists and turns to getting the engine out of and then back into the main housing I am not confident in my ability to deal with wet sealant and things falling apart while I wrestle the whole assembly into the main housing.

Because of this I am contemplating assembling the crankcase out of the main housing using spacers on the bolts. Once the sealant is cured I'll remove the bolts and install the glued/sealed assembly into the main housing. Is this a good plan of attack or should I attempt it all at once as in the repair manual?

Thanks,

Steve

 

[beavis331]

As long as you leave plenty of cure time.(at least 24 hours) And you are careful you should have no problems. What are you using for sealant?

 

[Ozhoo]

Loads of folks(including me) do it the way that you're pondering. Gives you a chance to pressure test it before proceeding as well.

 

[HarleyT]

There are not all that many twists and turns, just put it together like you read and be done with it.

 

[grack]

They are not bad just clean everything well first. i use dirko mainly everone has their preference .

 

[SteveSr]

What are you using for sealant?

Permatex Motoseal. It was recommended in several threads and is available at O'Reiley's auto parts unlike Dirko which appears to be exclusive to Stihl on this side of the Atlantic.

 

[SteveSr]

Loads of folks(including me) do it the way that you're pondering. Gives you a chance to pressure test it before proceeding as well.

I like the ability to test as well. At least if I screw up I'll know where without having to remove the engine again. Although once the saw is apart it isn't that bad.

 

[Chris-PA]

Because of this I am contemplating assembling the crankcase out of the main housing using spacers on the bolts. Once the sealant is cured I'll remove the bolts and install the glued/sealed assembly into the main housing.

That is how I do all of my Poulans, and I did my dad's MS250 that way too. I use Yamabond4. It's one of the reasons clamshells are so easy.

 

[Matt B]

I've used three bond 1104 successfully for sealing clam shell cases. With what ever sealant you use do so sparingly.

On a related note the OP and others might be interested in this query;

I'm about to rebuild an Echo 350T. As per below the manual suggests using Loctite 675 on the outer surface of the bearing/crankcase. Have never used an adhesive in this application on other clam shell rebuilds although I have seen evidence of a spun bearing in a stihl 023...

Is it critical to do so? Finding it difficult to source Loctite 675 locally.

 

[a. palmer jr.]

I have both Dirko and Motoseal but prefer Motoseal because it seems less messy. Put it on both surfaces to be sealed, allow a little time to set and put it together using spacers, let sit overnight, remove spacers and put it in the saw. I don't remember how many of these and the 1127 saws, done the same way.

 

[Matt_Ellerbee]

Subd.

Tackling a ms250 sometime next week. Doing all rubber parts and seals. Gonna have a nice little truck/Polaris ranger saw. Going to use locktite 515 as I have a tube already.

Any tips for pulling flywheel and clutch? Or just piston stop it,spin clutch off and flywheel nut and tap with hammer?

 

[a. palmer jr.]

I wouldn't use a piston stop on one of those smaller Stihls. What I generally do is use an impact wrench on the clutch without any stop. Make sure you turn it clockwise to remove it though. On the flywheel I just remove the nut and hit the flywheel on the non-magnet edge and it will pop right off. If you don't have an impact tool you might get away with putting a rope in the spark plug hole and stopping the piston that way.

 

[SteveSr]

Any tips for pulling flywheel and clutch? Or just piston stop it,spin clutch off and flywheel nut and tap with hammer?

Just what I did except use rope in the cylinder for a piston stop.

 

[Matt_Ellerbee]

That's what I was planning on using. Rope pushed in from center so the ends won't get hung in a port.

 

[BuckthornBonnie]

I've used three bond 1104 successfully for sealing clam shell cases. With what ever sealant you use do so sparingly.

On a related note the OP and others might be interested in this query;

I'm about to rebuild an Echo 350T. As per below the manual suggests using Loctite 675 on the outer surface of the bearing/crankcase. Have never used an adhesive in this application on other clam shell rebuilds although I have seen evidence of a spun bearing in a stihl 023...

Is it critical to do so? Finding it difficult to source Loctite 675 locally.


View attachment 538642

I rebuilt an 029 and saw evidence of a spun bearing. I used loctite on the rebuild (640? Not sure) but honestly the surface prep was tricky due to oil and dirko sealant not allowing perfect cleaning. If the recess is to spec and is torqued down, I doubt loctite is needed on most.

 

[Matt B]

Thanks for the input Buckthorn.

 

[SteveSr]

Well, the seals came in Wednesday and I had an opportunity to reassemble the engine last evening. Everything appeared to go well. I had to use a piece of scotch tape to get the new seal past the circlip groove on the PTO side.

I followed the instructions for the Motoseal. It really seemed too thin and tended to level itself out. I didn't have much choice at this stage. I let the assembled engine sit overnight and all day today.

This evening I sealed it up and attempted to do a pressure test and was greeted with an EPIC FAIL! It initially had a slow leak that got bigger. I checked around all of the seals and seams, found nothing, and finally resorted to a water bucket. Leaks can't hide from a water bucket!

The water bucket revealed leaks around two of the bolts. I pulled the engine apart again and found that the Motoseal had only hardened where it contacted air! The Motoseal was still almost completely uncured on the case flanges. Based on this performance it would appear that Motoseal is COMPLETELY UNSUITED for use in sealing crankcases for 2 and 4 cycle engines as it says on the package!

So now I just wasted another two hours cleaning the uncured Motoseal from all of the nooks and crannies of the castings.

So where to now? Dirko is $16/tube from the local Stihl dealer but has to be ordered. Others have mentioned Yamabond 4 and Hondabond 4? I am beginning to think that all of these formulations have been changed to comply with VOC and/or ethanol requirements so the stuff bought today may not be the same product as others have successfully used in the past.

It appears that what is required is a gasket MAKER that cures in the ABSENCE of air. A lot of these now appear to be gasket CEMENTS that never really harden which would make them unsuitable in this application as these surfaces don't completely touch and therefore any pressure would blow through the gap.

Your thoughts?

 

[BuckthornBonnie]

Dirko... Hondabond should be fine, too.

I think others have used motoseal with no issue... Sorry to hear your experience.

The loctite some may suggest may not be sufficient in this location (too large of gap).

 

[Chris-PA]

So where to now?

Go to the local Yamaha/Honda dealer parts counter and get a tube of xxxBond4 for $10. I've never had an issue with it.

 

[SteveSr]

I did some more research and actually dug up the manufacturers data sheet and MSDS for the Stihl Dirko HT. Based on the description this IS a high temperature RTV compound that fills gaps and will cure without exposure to air. The DS is silent on the resistance to gas and ethanol but apparently Stihl finds it appropriate.