Pistons: 1 at a time or all 4?

I've only done this twice, so still a rank amateur, but curious what you guys have done. When inserting pistons into the jugs, all the books say lower the jugs on to all 4 at once. This is what I did on the 1100 a while back, and of course it works, but was a two person job while wrestling rings and clamps, ring clocking be damned as I struggled them into place.

On the 750 I put the jugs on the upper case and dropped the pistons/rods in one at a time in the same manner as every other motor rebuild I've done (except the VW of course!). This was much more controlled and easier in my opinion.

If you are doing a top end rebuild only, obviously you don't have a choice, but if the case is already split, why would you ever choose to do all 4 at once?

And then just a photo for amusement...remember to put the chain guide tensioner bolt on BEFORE the jugs!

 

I set the pistons up so that the inner two are slightly higher than the outer two. That makes it a one-person job (for me anyway). I also cut some wooden blocks to use as cribbing so I can lower the head gradually and not risk damaging anything should a hand slip.

 

I do the same two inside pistons first and use wooden sticks to get the rings into the bores with the blocks below the pistons. Broke a piston ring on my Honda CB 750 four in the 1970's very cautious now .

 

Ditto that. Always done two at a time, never all four at once.
A lot depends on the chamfer inside the base of the liners, some makers do it better than others, so it all just slips on nicely.

 

When I say all 4 at once, I just mean dropping the jugs onto the pistons versus having the jugs already installed WITHOUT pistons, and then installing the pistons and rods one at a time from the top of the cylinder rather than the bottom.

This method just made more sense to me, and is the same as dropping pistons into a Chevy or Ford. I didn't know if I was missing some secret to the other method.

I did bolt the rods up to the crank while it was out of the case ahead of time to check clearance, and I don't see why you couldn't plastigage with the rods in the case other than it gets pretty tight to reach in there.

 

I don't think you would have the space to be able to do that. Let alone get two done and then rotate the crank to get the other two done. I would stick with having Rod, pistons and rings ready to go and then do the center two with the blocks of wood to help hold the pistons up. I just can't wrap my brain around the Chevy or Ford analogy from your above post. I don't think you can do that with this XJ motorcycle.

Would love to see some pics if you are going to do it the other way. Good luck, what ever way you plan on doing it. I would stick to the center two outer two method.

 

Did you replace the bolts I think they are one use. Must be easier to torque the big end caps on the Chevy and Ford's if the bolts are not upside down unlike some of our bikes.

 

The rod bolts? I reused them. If they're single use I must have missed that in the book.

 

I already did it, and it was easy. That's why I posted the question, wondering why this isn't the normal method, or at least more common.

If rod bolts aren't reusable as Franz says, that could be a good reason.

 

I am not 100% sure I just don't want you having problems with your rebuilt motor. I will have a look at the manual when I get home.

 

I also wondered if maybe this could only be done on certain models/years as it does require that the big end of the rod is small enough to drop through the cylinder. The rod was about 59mm (going from fuzzy memory here) so it easily fits the 750 bore, and the same rods would fit through a 650 bore.

 

@Roast644 see the note at the bottom of the page it does not say bolts should be renewed.

https://www.xjcd.org/750RH_crank_bearings_repair

For future reference.

https://www.xjcd.org/index.php/

 

Thanks for checking @Franz. I just looked in the Haynes book also and it does say this...



So they recommend new bolts, but from the wording I don't gather this to mean they are originally TTY, or designed as a single use. At any rate, they're in and I'm going to run them, and if they come apart it will certainly be a learning experience.

Didn't get any photos when I assembled it, but just now took a pic with the parts motor to illustrate. To slide the rings into the bore a ring compressor obviously is used since there's no taper on the top.

 

I printed some of these "piston holders" that hold the piston under the skirt while you get them in the cylinders. First doing 2 and 3, then 1 and 4.
https://www.thingiverse.com/thing:4365062

They work pretty well. Nothing special about them, similar devices could be made out of wood.

 

The pistons need to go into place before putting the cylinders on. This isn't a car engine.

 

That's what the book says, but why? That's why I asked this to begin with. It works, so if there's a reason that I'm missing, what is it?

 

Probably got a lot do with having to align the cams once the head goes on.
Can see it being more fiddly jostling everything upside down with no head attached to join the cases and bolting the rods into the crank.

Sounds harder to me at any rate.

 

Well I thought it was easier anyhow, and that's how I will do my next one also. I guess if somebody had a motor to put together, give it a try and see what you think.