On the road again at 40.............the bike that is

Rob, downloaded and studied your pics.

Please revisit this post:

http://www.xs650.com/threads/on-the-road-again-at-40-the-bike-that-is.49360/page-10#post-515147

In our old shop environment, those cylinders would warrant an instant bore job. Wouldn't even bother measuring. Going with crusinimage 2nd over set, you can ignore trying to save the old pistons and pins. But, you can use the unblemished outer parts of your old pins to evaluate the conrod small ends.

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/131956383746

If you manage to get this kit (limited availability at this moment), you can use its wristpins to evaluate the conrods.

The crusinimage delivery is surprisingly fast. Can you arrange acquisition thru a nearby member?

Edit: IMPORTANT - I'm assuming that your cylinders are stock bore. Need to measure them to be sure that they haven't already been bored, otherwise may need to go to 1.0mm over...

Replace the front guide. Use the recommendations from the senior/guru members on your choice of gasket set.

Completely decoke/clean the head and valves, then closeup crisp/clear pics of head seats, valve faces, stems, end.

Lighting angles, reflections, oily surfaces always throw me off. After cleaning/degreasing, need good pics of the cam lobe surfaces, rocker pads, adjuster tips.
 
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Thanks Pete. That's the plan after clean up. Can't fool cruizinimage with a PO box thats not linked to a Paypal account but maybe have a US buddy or two who will help.
 
Hey 2M, Thank you very much for your speedy reply and wisdom again.

TwoManyXS1Bs said:
Please revisit this post:
Click to expand...
Yup, that's what started all this.....lol.

TwoManyXS1Bs said:
But, you can use the unblemished outer parts of your old pins to evaluate the conrod small ends.
Click to expand...
I will do some searching on how to do this. I'm guessing we're looking for play/slop?

I'm sure purchase can be arranged through some forum contacts once I know for sure what to get.

Front guide is already in my shopping cart, along with some other goodies, just have to pull that trigger.

Gasket kit already here as recommended by 5twins along with valve seals and the requisite tools he recommended.

I will get to cleaning and then post some more pics of the items you noted, and will then get them to my machinist for some measurements so we know if they're stock and then what to get. I don't think anyone has been in here before, but certainly am no expert on what to look for to determine that.

Once again, Thank you for your advice.
 
A little scuffing and some scrape marks on the pistons and in the bores is pretty much normal but I think yours are pretty bad. The scraping on the pistons usually begins near the bottoms of the skirts on the front and back side. The area the scrape marks cover grows as wear increases on the pistons and in the bores. Looking at yours, they are pretty much fully covered. What causes the scraping is too much cylinder to piston clearance. This allows the piston to rock back and forth on the rod as it's pushed up and pulled down by it. When new, with tight clearances, the piston doesn't rock as it goes up and down, and no scraping occurs.

The discoloration on the pistons below the rings indicates blow-by. The partially clean top on one of your pistons indicates oil was getting to it and washing/keeping it clean. In your pics, that piston does look wet with oil on top, as does it's corresponding combustion chamber.

Yes, measure things up, but I think you're going to find those bores and pistons out of spec.
 
Thank you for all that info 5twins. I appreciate it. I guess it's pretty surprising that it ran as well as it did...lol.

I will do my best to get things cleaned up, post some pics for you guys and then get my machinist to measure things up.
 
Can't read the piston tops yet, and couldn't see anything on the sleeves.
 
You can measure across the skirts to get a close idea of bore size.

PistonMeasure01.jpg

PistonMeasure02.jpg
 
OK then. The bores on these are just over 75mm, as in 75.xxx mm. The 3 digit numbers you find stamped on the parts are the fractional portion of the measurement and will replace those 3 x's. So, your original bore size when new was 75.010 mm. The new piston to cylinder clearance spec is .050-.055mm. The pistons are just under 75mm, as in 74.xxx. That means you will want to find something between 955 and 960 stamped on your piston tops. I think I can just barely make out 959 on one of them. That would have given a new clearance spec of .051mm.

Measure the parts now to see what they've worn to. The piston begins to wear 1st and usually more because it's softer than the steel bore. Eventually it's rocking and scraping will start wearing the bore. Minor wear would show as a small patch of scraping on the front and back of the piston near the bottom. The bores would have a small amount of scraping about midway up the stroke. Your bores look scraped pretty much the entire length of the stroke.

A "quick and dirty" check for wear can be done by sticking the cleaned piston back in the bore, rings removed, and seeing how large a feeler gauge you can jam down in between it and the cylinder wall. .004" is about the most you want to see. Above that indicates excessive wear and clearance.
 
5twins said:
A "quick and dirty" check for wear can be done by sticking the cleaned piston back in the bore, rings removed, and seeing how large a feeler gauge you can jam down in between it and the cylinder wall. .004" is about the most you want to see. Above that indicates excessive wear and clearance.
Click to expand...
That "quick and dirty" method works well. I'd add two things to that... First, find some "tapered" feeler gauges. You'll get a more accurate measurement. Second, If that's good you'll need to repeat that after dressing up the piston and honing the cylinder to make sure you didn't clean your way past the max allowable clearance.
 
Wow, this is great info 5twins. Your explanation makes it very easy to understand. I have been reading about piston/bore sizing but now understand how all those numbers relate.

Will get some clean up done this weekend and post measurement results.

Thank you.
 
Ok, thanks Jim. I have a few sets of feeler gauges but will see if I can track down a tapered set.

This quick and dirty method may very well provide some answers without bothering with a machine shop measuring things as 2M suggested.
 
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