cylinder walls

Alright XJ wizards, I need your help again. I've spent the past couple of days honing my cylinders out in anticipation of getting new piston rings. I was just wondering if you guys wouldn't mind looking at these pictures and letting me know what you think. Thank you.











And just for fun here is my baby as she currently sits, so naked but with new handlebars and grips.

 

Also, I measured the inside diameter of the cylinders at the top and the bottom. Both ends on all 4 cylinders are right around 63 cm. Assuming the cylinders look honed out well enough can someone enlighten me as to what size piston rings I should order?

 

63mm is the standard bore size for a 650, so you would use the standard size rings............although oversizes are in .25mm increments (63.25mm, 63.50mm, 63.75mm, etc.) so "about 63mm" isn't all that accurate enough!

Ring sizes should match the piston size, and piston size is matched TO the bore. It is common for new pistons to not be "exactly" 63.00m or 63.25mm etc., and therefore the procedure is to:

a) order the new pistons
b) measure them, exactly.
c) hone or bore the cylinder to the ACTUAL piston size + the specified skirt clearance
d) fit the piston rings to the piston wall and size them (file the gap) to the specified clearance.

 

I don't plan on replacing the pistons, just the piston rings, do I NEED to replace the pistons as well? I am working out of my garage and don't really have the tools to bore out the cylinder walls. The hone I am using is a glaze breaker that I understood to just be used to break the glazing inside the cylinder so the new rings will seat properly.

 

The pistons look ok. If so then you can just re-ring it. You should still check the ring gap as Chacal has suggested. Place the ring one at a time in the prospective cylinder at the top. Read the gap. If too tight they will shatter so you'll have to file the end of one side to get the gap right. Check the book for the proper spec. Make sure you file the rings squarely. Some auto parts stores have ring gap tools. You put the ring in and turn the crank and the wheel files the gaps stright. Just get them in spaec and don't go too much.

 

So you are saying at this point I should go ahead and order the standard size piston rings?

 

My opinion is that I think you need to hone a little more.
The hone marks also look a bit deeper than I'm used to, but that could just be the camera.
It's been a long time since I have honed a cylinder, but IIRC, the engine guy that was helping me told me had me lube the hone with...something. I can't remember if it was penetrating oil or cutting oil or diesel fuel?
Someone that knows what they are talking about should chime in before I steer you wrong.
There are also different stones (course or more fine). Depending on how much you need to take off, will let you chose the tool.
Technically, you shouldn't be able to see where the piston has normally stopped on it's travels.

 

The proper piston-to-wall clearance is:

.030 - .050mm (.0012 - .0020")
MAXIMUM CLEARANCE ALLOWED: .10mm (.0039")

The proper ring end gap clearance is:

Top:
.15 - .35mm (.0059 - .0138")
MAXIMUM CLEARANCE ALLOWED: 1.0mm (.0394")


Center:
.15 - .35mm (.0059 - .0138")
MAXIMUM CLEARANCE ALLOWED: 1.0mm (.0394")


Lower:
.3 - .9mm (.0118 - .0350")
MAXIMUM CLEARANCE ALLOWED: 1.5mm (.0591")




The proper ring side clearance is:

Top:
.03 - .07mm (.0012 - .0028")
MAXIMUM CLEARANCE ALLOWED: .015mm (.0059")


Center:
.02 - .06mm (.0080 - .0024")
MAXIMUM CLEARANCE ALLOWED: .015mm (.0059")


Lower:
none specified
MAXIMUM CLEARANCE ALLOWED: none specified

 

Jon, here is what I would do:

a) take those jugs, along with the pistons, down to a local machine shop and ask them to measure:
1) each piston
2) the corresponding cylinder hole for each piston, both upper and lower bore and taper (there's a spec for that, too!).

Having a competent machine shop just do the measurements shouldn't set you back more than $25, especially if they:

i) like you, or
ii) have a cute girl along with you, or
iii) seem like you might be interested in having them do some further work............


Then:

b) compare the measurements. Remember, you need a certain piston-to-wall clearance; and like Goldilock's porridge, not too much and especially not too little.

c) if the clearance is too small, then more honing is required.

d) if the clearance is too large, then you should follow the previous recommendation.....meaning new pistons will be required, new rings, and a further hone and/or boring to the proper size to match the new pistons that you'll be needing.


The above is THE correct way to do things.

 

Mike, I am using PB fluid to lubricate the hone, and the stones are 220 grit.

Chacal...I do have a cute girl to take with me, but she seems endlessly bored by what I am doing. Do you think it would be in my best interest to buy a good precise digital caliper like THIS so that I can take the measurements myself, especially if I am going to need to keep remeasuring as I work more?

 

Hey Jon, well, calipers like those aare VERY handy to have, but to measure the cylinder bores, a machinist will actually use a bore gauge rather than a set of calipers.

Maybe she just needs to be honed, rather than bored? 8O

 

ROFL Chacal!!!

 

If he's just "re-ringing" a not-too-worn out motor, he shouldn't need to refit his pistons; he sure can't ADD material anywhere so better to not over-hone; and just be sure to correctly gap the rings. It should be fine. If NOT then he's have to buy new pistons anyway which shouldn't be necessary unless the poor thing was horribly worn.

In answer to the original question, I would hone a BIT more, to remove all traces of where the pistons had been stopping; and try to get a slightly wider angle on your cross-hatch.

Stock size pistons will require the stock rings; but the gapping advice is right on; checking/adjusting the ring gap is ABSOLUTELY necessary.

I would also take the cylinders to a machine shop and have them checked with a bore gauge. Record the findings. Drop the jugs back on the "naked" pistons and check piston-to-wall clearance; as long as it's not too great then proceed as planned.

I think you'll be fine. If NOT then you'll be looking for new pistons too, and my advice no longer applies.

 

psshhh...She'll get over it

I took the block and pistons down to a machine shop here in town and the guy said the fitment was fine between them and that I should stick with standard sized piston rings for replacement. He did recommended that since I have been using a 220 grit stone on the cylinders that I should up it to a 400 to clear up the scratches the rest of the way and to finish honing it out. I also dropped my head off to him so that he could do the valve job for me. I have heard from quite a few people that it's the best machine shop in town so I'm confident they will do good work. I can almost start to see the light at the end of the tunnel...for this part .

 

If the piston skirt clearance was too great, didn't they use to knurl the skirts? Haven't heard anything about that in years, probably wouldn't be advisable on these high revving engines though.