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Discussion Starter · #1 ·
Last thread of the night Fellas, I promise.

Final issue (I hope!) that I am having with my engine ('72 CL350) is my pistons. I've not ridden the bike since I purchased it. Have had it started a number of times but no luck throwing a leg over her due to some ignition & spark issues . . . did I mention there are other problems with it? ;)

During my attempt to get this going only the right cylinder was getting a spark and firing. Due to the other issues going on I never really had the bike running for more than 45-60 secs before she would die. I know the issue now (bad coils), but doesn't explain some of the marks on these seemingly new pistons.

The PO had the cylinders bored out, head machined, and new pistons & rings installed - by whom I am unsure. He got the pistons through Bore Tech. They appear to be one size oversized (+0.25). I've checked the ring gaps and they all fall into spec. I do not have a micrometer to check the pistons nor cylinder but did measure the best I could with a calliper.

IMG_1617.jpg

IMG_1620.jpg

Scuffs on the non-firing piston.

IMG_1621.jpg

Dings on the piston skirt (firing side)

IMG_1624.jpg

Ding on non-firing side piston skirt. Possibly could have gotten dinged during installation.

IMG_1623.jpg

IMG_1625.jpg

IMG_1626.jpg

IMG_1627.jpg

IMG_1628.jpg

As per the FSM, standard value is between 63.97 - 63.99. Based on my finger and toe counting, that would give a +0.25mm oversized piston a tolerance of 64.22 - 64.24. However, from my measurements, which again I used a calliper, and did across the piston pins and again perpendicular appear to be somewhat larger. That all said, I did not measure the cylinder (it's soaking to be cleaned up.

Left piston measure at 64.90 and 64.57 (across the piston pin)
Right piston measure at 64.97 and 64.56 (across the piston pin).

Thoughts please?
 

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Those pistons are suffering from poor installation practices. Dings from miss handling and scuffs from dirt in the cylinder. You measure pistons 10mm up from the bottom of the skirt perpendicular to the wrist pin. To measure piston to cylinder clearance just use a feeler gauge between the piston and cylinder. You should have some drag with a 0.002" feeler gauge.
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I think the dings could be blended out. Pretty sloppy work by the PO. Noot an expert on the 350 or what Bore Tech uses for pistons, but the valve relief looks pretty deep. We have run into a case on this forum where a member purchased a 'rebuilt' but not running right 350. Turned out he had Wiseco 13.5 to 1 CR pistons for an alcohol engine. You might check with Bore Tech and see what you have.
 

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Double check the rings are installed the correct side UP.
There shuold be marks that indicate the TOP side.
If they are installed wrong you will have long term compression problems.
 
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Discussion Starter · #5 ·
Thanks for the feedback guys.

piston1.jpg

Did some measuring and confirming based on the FSM:
- piston ring side clearance for all three rings are within spec
- piston ring end gap for both pistons/cylinders are within spec (0.2 - 0.4mm); mine were 0.330mm on the left, and 0.279mm on the right
- ring thickness is good for all

Confirmed that the pistons and rings were purchased from Bore-Tech by the PO. As per the Bore-Tech page:

Ring Alignment (2)_Fotor.jpg

So no markings on the rings to orient them. Weird. I had a hard time telling the colour but got it sussed out.

Checked the piston to cylinder clearance - and it was exactly at 0.002 mm like you said it should be Tools.

Cylinders appear to have good cross hatching:

cylinder1.jpg

cylinder2.jpg

So, if everything looks good I will spend some time repairing the dings and scuffs on the pistons.

Oh, here are the nasty old pistons:

piston3.jpg
 

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Nah, not stupid... I thought we were supposed to go full metric by the time I was an adult, as told to us in school in the '60s and early '70s, but it never happened - and now we're one of only a few holdouts
 

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Yeah the whole SAE vs. metrics thing drives me nuts. I HATE working on American cars and bikes for this very reason since I could never keep it straight on all the various sizes (1/8", 5/32", 3/16", 13/64", ....)

Makes my head spins LOL
 

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and there are few true cross-references, like 13mm and 1/2" (not exact but really close) or 14mm and 9/16", 7/16" and 11mm, 5/16" and 8mm... just find one that fits! :D
 

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And that is why most things that require high-precision use metrics for measurements.
 

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Discussion Starter · #12 ·
Funny thing up here is most people weigh themselves in pounds and their height in feet & inches. In the UK and New Zealand they also use "stones" - just to make it more confusing. Most contractors that I've worked with/for also use inches and feet, but then throw in metric measurements from time to time. ;)

Everything else is metric. Though.....since today is the first day in cannabis legalization, both recreational & medicinal, I wonder if they're measuring by grams or ounces? I know on "the street" (don't ask how I know) they sell by the ounce....well, if you're buying a lot! :eek: But that is a totally different thread.

Thanks for the help Fellas!
 

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Feet and inches is used in construction because a foot (12 inches) can be divided evenly by 1, 2, 3, 4, 6, 12. Also a 4'X8' sheet of plywood can be divided by 1, 2, 3, 4, 8. evenly. Try that with the metric system based on "10".
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Yeah the whole SAE vs. metrics thing drives me nuts. I HATE working on American cars and bikes for this very reason since I could never keep it straight on all the various sizes (1/8", 5/32", 3/16", 13/64", ....)

Makes my head spins LOL
Add to them the whitworth sizes I have for my old Brits...lol
 
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