Rotax 657X Motor Bottom Case

[teamgreen737]

Hello all, I'm trying to find the bottom half of the bottom case for my 95 GTX. I had the bottom end go and a rod punctured through it. I've been scanning ebay a little bit with no luck. If anyone has one sitting around or knows where I can find one, please let me know. I'd appreciate it!

 

[seadoosnipe]

Casing halves....?

Do you still have this bottom half? If so, you need to take it down and have it built up by welding, then cut back down to the specs you need.

The reason? The upper and lower halfs of the Rotax engines are not interchangable. The two pieces are machined together. If you've looked for one to replace the one you need, you'll notice you can't find one.....because it's like I said above, each one is individual of each other and machined that way.

 

[PWCdoc]

I agree. The case halves are machined as an assembly and using mismatched case halves will possibly torque the crank in a manner in which it is not intended and/or not allow them to seal properly. I think I have a set here but if not, I'm certain someone else might.

 

[teamgreen737]

Do you still have this bottom half? If so, you need to take it down and have it built up by welding, then cut back down to the specs you need.

The reason? The upper and lower halfs of the Rotax engines are not interchangable. The two pieces are machined together. If you've looked for one to replace the one you need, you'll notice you can't find one.....because it's like I said above, each one is individual of each other and machined that way.

I haven't looked at it for a good while, I thought the bottom half of the bottom case really had no spec'd surfaces other then being matched to seal against the top half of the bottom case and just served as a catch for oil lubricating the crank.. I will have to take a better look at it when I get back home. I do know an excellent welder in the area who could possibly hook it up.

Thanks for the help guys.. I'll take some pictures when I get home also.

 

[ski-d00]

clean holes and chunks missing are not a problem to fix for a good tig guy, when you get cracks up to the parting line of the cases it gets trickier.

it's true that all case sets are line drilled while bolted together so their mating surfaces are perfect. but with that said, I have checked non matching case halves for alignment by blueing, clay, and plastigage and have been amazed how well they match up, generally within a couple thousandths which is more than acceptable to use. So, if you're careful and check the case alignment thoroughly, you can use mismatched halves.

 

[teamgreen737]

clean holes and chunks missing are not a problem to fix for a good tig guy, when you get cracks up to the parting line of the cases it gets trickier.

it's true that all case sets are line drilled while bolted together so their mating surfaces are perfect. but with that said, I have checked non matching case halves for alignment by blueing, clay, and plastigage and have been amazed how well they match up, generally within a couple thousandths which is more than acceptable to use. So, if you're careful and check the case alignment thoroughly, you can use mismatched halves.

Thank you for the great advice. This guy used to repair my aluminum radiators on my dirtbikes. I'm sure he can tackle this no prob.

 

[PWCdoc]

So, if you're careful and check the case alignment thoroughly, you can use mismatched halves.

Very Very VERY bad advice!!! However, feel free to give it a shot. Just remember we told you not to mix and match case halves.

 

[robin savell lloyd]

Very Very VERY bad advice!!! However, feel free to give it a shot. Just remember we told you not to mix and match case halves.

Doc I have read many of your post and I respect what you have to say as you seem to allways have very good info. On the other hand I am also reading what seems to me to be a well thought out idea from ski-d00. He seems to have a highly Intellectual thought out idea. If he is wrong please share some science to this subject that will prove him to be wrong if you can. Now on the other hand I would not even try to repair this engine that has had the rod go threw it as I would think I could locate a good used ski with a good bottom end. I would have alot of parts left over. I am sure that you can prove me to be wrong but I sure would like to know about this subject on the 657x engine so that I will be able to get it right. Sure would like to hear from the pros like Seadoo Snipe Kustomkarl, Dennis, Chester and other pros. Thanks Robin :cheers: :boxing_smiley:

 

[seadoosnipe]

Hmmmm,....?

Very Very VERY bad advice!!! However, feel free to give it a shot. Just remember we told you not to mix and match case halves.

I don't think that's the case with a crank that has so many bearings and seals sandwiched in between them. I think, a few thousandths would be detrimental to a motor that turns out over 6K rpm.

If you choose to go that route, make sure the guy that used to weld up your dirt bike has full machine shop experience in reading precision measuring equipment ....and has it.

I don't think I've ever heard of an engine case that was split and used elsewhere and actually worked. I know I've seen it tried. As soon as you start to torque the bolts, the shaft will seize. If you don't spin the shaft one revolution after every torque, then you'll not know it till you get it completely together.

 

[robin savell lloyd]

I don't think that's the case with a crank that has so many bearings and seals sandwiched in between them. I think, a few thousandths would be detrimental to a motor that turns out over 6K rpm.

If you choose to go that route, make sure the guy that used to weld up your dirt bike has full machine shop experience in reading precision measuring equipment ....and has it.

I don't think I've ever heard of an engine case that was split and used elsewhere and actually worked. I know I've seen it tried. As soon as you start to torque the bolts, the shaft will seize. If you don't spin the shaft one revolution after every torque, then you'll not know it till you get it completely together.

Very good point Louis I have seen this problem before on small trans.

 

[Chester]

I also agree, no mismatched cases unless you line bore them. Also, you would have to machine the rotary valve surface.

Chester

 

[robin savell lloyd]

I also agree, no mismatched cases unless you line bore them. Also, you would have to machine the rotary valve surface.

Chester

Very good info chester :agree: another thought is If the rotary surface or one of the halves of the crankcase have ever been machined it would realy be off when you tried to put it back together.

 

[robin savell lloyd]

Very Very VERY bad advice!!! However, feel free to give it a shot. Just remember we told you not to mix and match case halves.

Pwcdoc is correct If you want to do it right use a matching set. Any thing else that has not been machined is asking for trouble. :agree:

 

[PWCdoc]

The way cases sets are made is very important for proper assembly. The parts start out as a casting of 2 parts. The mating surface between the case halves is then machined and the mounting holes tapped. Then, the case halves are assembled and mounted onto what is called a tombstone that may have 4 sets mounted on different sides in a CNC machine where all of the remaining surfaces are machined. Then, the still assembled case set is line bored for the crank and crank seal surfaces. If somehow, and it's very possible, that one particular line bore operation is off "a couple of thousandths" then the risk you take by using mismatched case halves include putting the crank in a bind when torqued down resulting in a broken crank, crank seals not sealing properly leading to a potential seizure, bearing load surface not distributed evenly resulting in shortened lifespan of bearing components and in the case of the Rotax, the RV surface being off "a couple thousandths". And when that RV timing plate is spinning around at 6,000 rpms it's going to catch one half of the cases and eventually cause more problems.

Now, you can buy a mismatched set of cases and machine them to work but for what you're going to spend in welding and machining...why not just purchase a properly machined set from the get go and save money, hassle, and worry about when it's going to fail because shortcuts were taken?

 

[ski-d00]

I didn't mean to cause an uprising and I hope nobody here misunderstands what my point is on this subject and I will explain in detail for anyone who cares to read. If you would have asked me this same question a few years ago I would have said that you could NEVER used mismatched cases, period.

I've heard of people doing it which made me curious and had 2 951 cases that I was rebuilding so I thought I'd switch them real quick and take a quick measurement with my bore guage on the bearing surfaces and that would be that.

Well, to my surprise, the bearing diameters were within .0003" (yes, 3/10 of a thousandth) and was getting about that same variance between the 2 matched case halves and between different bearing journals. I couldn't believe this so I kept measuring and cleaning surfaces to a polish and trying different measuring methods and continued to be very surprised. The only real measurement that was off .002" was the side to side alignment measurement but is corrected through the bolt hole alignment when the 2 halves come together on the bearings, so no big deal because there's much more clearance than that between the shoulder of the bolts and the hole. I couldn't measure all surfaces, like the seal areas but they appeared to be dead on using clay, certainly close enough to make a good seal. Ultimately I concluded to my satisfaction that these 2 mismatched sets would work together.

Now, I didn't actually build them mismatched so the real proof would be in the pudding, but I'm not that stupid to used mismatched cases when I don't have to and still have never used mismatched halves and probably never will. If I did, it would be because there was no other feasible option like they don't make them any more and there's no chance of buying a used set and even then I'd spend hours measuring and remachine if necessary.

Now, it is possible that there is some luck involved with the 2 sets I had, they were both from 98 model year skis, but I'm not convinced that luck is the real answer. I haven't really had a chance to measure 2 more sets since I normally build them one at a time but I would like to measure another set that were made several years apart.

Take this for what it is worth but I no longer say that it can't be done. I also would never recommend it.

 

[robin savell lloyd]

I didn't mean to cause an uprising and I hope nobody here misunderstands what my point is on this subject and I will explain in detail for anyone who cares to read. If you would have asked me this same question a few years ago I would have said that you could NEVER used mismatched cases, period.

I've heard of people doing it which made me curious and had 2 951 cases that I was rebuilding so I thought I'd switch them real quick and take a quick measurement with my bore guage on the bearing surfaces and that would be that.

Well, to my surprise, the bearing diameters were within .0003" (yes, 3/10 of a thousandth) and was getting about that same variance between the 2 matched case halves and between different bearing journals. I couldn't believe this so I kept measuring and cleaning surfaces to a polish and trying different measuring methods and continued to be very surprised. The only real measurement that was off .002" was the side to side alignment measurement but is corrected through the bolt hole alignment when the 2 halves come together on the bearings, so no big deal because there's much more clearance than that between the shoulder of the bolts and the hole. I couldn't measure all surfaces, like the seal areas but they appeared to be dead on using clay, certainly close enough to make a good seal. Ultimately I concluded to my satisfaction that these 2 mismatched sets would work together.

Now, I didn't actually build them mismatched so the real proof would be in the pudding, but I'm not that stupid to used mismatched cases when I don't have to and still have never used mismatched halves and probably never will. If I did, it would be because there was no other feasible option like they don't make them any more and there's no chance of buying a used set and even then I'd spend hours measuring and remachine if necessary.

Now, it is possible that there is some luck involved with the 2 sets I had, they were both from 98 model year skis, but I'm not convinced that luck is the real answer. I haven't really had a chance to measure 2 more sets since I normally build them one at a time but I would like to measure another set that were made several years apart.

Take this for what it is worth but I no longer say that it can't be done. I also would never recommend it.

You did not cause a uprising! What you did was to get others thinking and shareing their view points. I do believe that with your knowledge that you would be fine mixing cases as you know what you are looking for as some of the beginers that may try this could get it wrong. You have the tools to check how true the surfaces are and you have the know how. As you have said that you may have also been lucky that they were the same years and that neither of them have been to sbt or any other machine shop and had any thing done to them because if they did then your measurements would have been different. I can allways be wrong but it sure is nice to get other points of view so we can further our knowledge on how all of this works Robin :cheers: