Splitting Crankcase WITHOUT removing cylinders and top end.

[BigMacDouble]

Hey there ,

this might be a pretty dumb question. As you might notice from my other posts I’m pretty new to the world of motorcycles.

I got a little too hasty and joined the crankcases before I had my hands on a torque wrench . Only after I had the entire engine finished did I remember I left the big end bearing bolts completely loose since I was going to tighten them when I got the wrench.

I’d prefer not to take the entire thing apart again . I’m thinking if I split it the crank will lift off with the top and cylinders and I can access the bolts . Am I missing something that makes this impossible? Or could this lead to damage maybe from the cam chain holding the weight of the crank?

Any advice would help!

 

[amc49]

You can generally do it but not like you say. Not dead sure on that engine type but be sure to loosen any case bolts that go in from the top first then flip engine upside down. The cylinders will prop it up at an easy to get to angle and you loosen bottom case and pull the THAT off leaving most everything still in place.

It gets done all the time.

 

[BigMacDouble]

You can generally do it but not like you say. Not dead sure on that engine type but be sure to loosen any case bolts that go in from the top first then flip engine upside down. The cylinders will prop it up at an easy to get to angle and you loosen bottom case and pull the THAT off leaving most everything still in place.

It gets done all the time.

Its a 1978 xs400E

What would i need to remove besides the side casings? I can leave the clutch intact? Or the kickstart?

 

[xschris]

Your going to need to remove anything that keep the cases from splitting. Did you replace the rod bolts with new ones? Those should really be replaced as they stretch after being torqued. You don't want those to break. I would also hope you checked all the plane bearings for clearance. Using old ones or not checking for gap with new ones is another no no. You might get lucky but if your going that deep in the motor better to do it right.

 

[amc49]

I' myself am leery of just changing rod bolts on a stock engine. Yes if hotrodded but no if not. When you yank rod bolts the new ones do not go in exactly the same and why standard best mechanic's procedure is to remachine the big end again for round if the bolts are changed. Besides, the bolts are NOT TTY one use bolts and they will simply pull up tight again at the tighten, I'd be specifically looking for any fall-off in torque while tightening them up, it shows you a weak bolt that needs changing.

Unless of course somebody knows for sure the OEM rod bolts are super weak in these, I for one cannot say. Most Japanese rod bolts will rebuild to a stock engine for another go-round just fine.

A thought for solid comparison..............the world has now gone to TTY bolts in almost anything internal in engines and largely a plan to force the sale of a lot more parts as well as forcing you to buy new car when you can't get them any more. A TTY (torque to yield) bolt is one that tightens up intentionally to slightly past the point the bolt material begins to 'yield' which is a fancy way of saying ot is about to snap in two and designed on purpose that way. They are no longer stretched, but past that physical state to now be in the state beyond that, or beginning to yield (fail). The engineers give you some crap about the bolt being more stable there but these are the same engineers who time and again have proven they cannot design spit to stay together, and maybe even intentional. Look at the major design issues coming out in the last 20 years, engines and transmissions that break left and right and cannot even go 40K miles without you walking home at least once. The 'rule of McDonald's' engineers. TTY bolts are part of that, to force you to go megabucks DYI and the OEM then gets twice as much in repairs too paying for parts you used to be able to reuse over very reliably. I for one hate those bolts, you pay more for them, for ultra trick parts designed to break in half easier, think about that. It's bullsh-t.

FYI, if the part is a standard oldschool part, the ending tightening action will be in a torque number like ft.lbs. If it is a TTY bolt the ending will be in an angle ('15 degrees' as an example). Why the angle? Because the bolt is in yield mode, meaning you no longer can use a torque as the bolt has quit stretch mode, more torque will simply pull the bolt further into two pieces; the torque will be going BACK DOWN. You go angle instead to get all bolts to the same 'torque' but you really can't even call it that any more.

 

[BigMacDouble]

I've gotten new bolts just didnt tighten them and got ahead of myself before joining the crankcases. Thank god i remembered because they were finger loose. I checked all the journal bearings for the crank and theyre all good according the clearances in the manual .

Another question though. I noticed a bit of the silicone gasket sealant got onto the journal bearings on the crank. I was careful to put less near the mating surfaces near them but it seems some still got on them . How could i avoid this? I know to have the dowels in place to avoid any getting into oil passages but im not sure about getting a good seal and avoiding the more exposed bearings. Its ok to get it on the outside of the frictionless transmission bearings i assume though?

Thanks again.

 

[amc49]

You must clean off any plain type (journal) bearing it got on.

When you spread sealer you stop short of bearing shell, you don't go all the way to edge of the bearing shell dropoff point. And spread it super thin there. As well, you need to learn to grasp where sealing is needed and not needed, there are places where you put nothing on the split surfaces at all. You only seal to the outside and wherever it may be needed for oil pressure to not leak.

I often stop short up to an 1/8" when coming up to a bearing surface.

 

[BigMacDouble]

You must clean off any plain type (journal) bearing it got on.

When you spread sealer you stop short of bearing shell, you don't go all the way to edge of the bearing shell dropoff point. And spread it super thin there. As well, you need to learn to grasp where sealing is needed and not needed, there are places where you put nothing on the split surfaces at all. You only seal to the outside and wherever it may be needed for oil pressure to not leak.

I often stop short up to an 1/8" when coming up to a bearing surface.

Thanks!