Author Topic: How To: Splitting engine without removing top-end  (Read 1364 times)


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How To: Splitting engine without removing top-end
« on: April 07, 2020, 02:48:17 am »
Splitting the engine
So this went from a question to a How to.
Managed to split the engine today without removing the top end.
All you have to remove is both side covers.
All the casing bolts (some on top, some on the bottom).
Make sure you set the engine steady upside down.
Remove the balancer adjuster bolt and spring (see picture)
What I did to eventually get the cases to split was reinstall the bolts that normally bolt your engine to your frame so you have something to tap with a rubber hammer.
The cases split nicely and all the internals look in very good shape.
Unfortunately I did have one of the axial bearings, or set rings as honda calls them, break and I had to search around the block for all the pieces. One was wedged between the camshaft chain and guide and after I finally wiggled it loose with a needle it dropped down towards the head. Will get that later.
When I am ready to reinstall the bottom half again I will post here to show what you need to do.
« Last Edit: May 03, 2020, 09:19:30 am by kansloos161 »


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Re: Splitting engine without removing top-end
« Reply #1 on: April 09, 2020, 10:23:19 am »
Good luck!

No specific advice, though I've known plenty of folks who've done this on other makes/models.

I suspect you'll want to remove the clutch at least, and pulling the alternator rotor probably isn't a bad idea.  Often there are bearing retainer circlips or plates that span the crankcase mating surfaces, and there may be some hiding behind clutch may be hiding some.  (I've done plenty of engine rebuilds, though I've always pulled the top end.) 

Please keep us posted on how it goes!
« Last Edit: April 09, 2020, 03:57:38 pm by patrino »


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Re: How To: Splitting engine without removing top-end
« Reply #2 on: April 15, 2020, 03:00:10 am »
Nice work, good for future reference.


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Re: How To: Splitting engine without removing top-end
« Reply #3 on: April 17, 2020, 11:21:38 am »
Wow, great info, thanks for the update and photos!


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Re: How To: Splitting engine without removing top-end
« Reply #4 on: April 20, 2020, 02:36:25 am »
Changing output shaft seal
When splitting the engine it is always a good idea to change the seal on the output shaft.
This seal is prone to leaking and due to the shape of it you have to split the cases the change it. Better do it when you have the cases open ;).

The seal in question can be seen in the first picture. As you can see mine was sprayed over a bit and in general not in the best shape anymore (you also see the nylon spacer I have to space the 520 sprocket).
If the gearbox is in neutral, you should be able to spin the output shaft freely, If it is not in neutral set the gears as in the picture in my first post. It is important that the gearbox is in neutral as you are going to remove the output shaft and you do not want to move the balancer shaft.
To loosen up the output shaft, gently tap the output side with a rubber hammer while keeping pressure on the balancer shaft to prevent it from moving.
You can now choose to either remove the shaft completely or leave it halfway in.

In picture 2 you see the shaft just loosened up and the seal removed without taking the whole shaft out.
If you choose to remove the whole shaft be careful not to disturb the balancer shaft.

I opted to remove the whole shaft as the surface where the seal needs to sit was a bit rough and cleaning it was easier with the shaft removed.
When taking out the shaft be careful, the left side (with the bearing with the hole in it) can slide of.

Clean up the mating surface of the shaft and also be sure to clean the chamfered edge as you are going to want to have this smooth to properly seat the new seal.
When pushing the new seal on be sure it seats correctly. The inner part wants to catch on the edge of the shaft and be pushed outward. If seated properly it should look like in the picture. I used a tiny bit of new engine oil on the inside of the seal to help it on.

Don't forget to clean the mating surfaces in the crankcase.

Refit the output shaft with the gears in the same (neutral) position, make sure the seal seats correctly in the crankcase and that the hole in the left bearing faces upwards.
Check if everything is installed correctly by turning the output shaft, when in neutral it should be able to turn smoothly.

Refitting the bottom end will be in part 3 ;)
« Last Edit: May 03, 2020, 09:19:06 am by kansloos161 »


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Re: How To: Splitting engine without removing top-end
« Reply #5 on: May 03, 2020, 09:17:05 am »
Closing the engine
Closing the engine again is not that hard but it is a bit fiddly. Your best bet is do some ‘dry’ practice runs without any sealant first to get the hang of it.
This was my method:
Install all 3 set rings on the bearings and not in the lower engine case.
Install the 2 dowels that will go into the bearings in the lower casing and tilt two bearing holes slightly towards the back of the engine (really slightly probably only 1 or 2 degrees).
Make sure the shift forks are in the correct spot on their shafts so the ends fit in the shifter drum.
Apply a thin layer of sealant on the edges of the lower cover. (First try a couple of times without sealant to get the hang of it)
Gently position the lower engine casing with the back-of-the-engine side on the upper casing, keeping the front-of-the-engine side lifted up so you can look down into the engine.
Sideways align the 3 shifter forks with the gears on the primary and secondary transmission shafts.
Now gently close the engine casings by lowering the front-of-the-engine side of the lower casing. The two rear shifter forks will automatically fall in the correct slots between the gears, you can check this through the sump hole.
The most forward shift fork needs some help to slot into the correct place, take a long thin object and push the shift fork a bit forward so it can seat correctly while you further lower the bottom engine casing.
The two halves should now rest evenly on each other, there might still be a small gap because not everything immediately seats perfectly.
Gently push down or lightly tap the bottom half to seat it further, don’t force it down, if you need to force it you need to start again because something is misaligned.
A gap like the one in the picture should close when you push on the bottom case and/or hand tighten the casing bolts.

Put the 4 main crankcase bolts in but only screw them in hand tight. (this should definitely close all gaps)
Check if you can still turn the output shaft easily (gearbox needs to be in neutral)
Flip the engine over and install all engine casing bolts torqueing them as described in the manual.
Flip the engine back upside down to install and torque all bottom engine casing bolts.
Install the automatic balancer spring and bolt.