broken ring. what to do?

[johnny gaijin]

my '75 cl360 wasn't running so i took it to the shop.
bad leak down test and bad compression. they pulled the engine and apparently i have a broken ring. the mechanic wants to bore out the cylinders and put in bigger pistons but it's gonna cost an arm and a leg.
i asked if buying this would be an option and he said no that w/o measurements there's no way of knowing if those pistons and cylinders are any good.

this mechanic is new to me so i just wanted to double check i'm not getting screwed.

what do you guys think?

thanks!

 

[Swapmeet Louie]

what he's saying is correct. with out measuring you would be putting a lot more faith in the seller, whom you've never talk too, than you mechanic.

 

[AlphaDogChoppers]

What is the condition of your bores? What is the condition of your pistons? What is the piston clearance? YOUR OWN pistons and cylinders need to be measured. THEN you can intelligently decide on whether you really need a re-bore, or if you can just re-ring.

Ask your mechanic what the piston clearance is. Is there a wear ridge at the top of the jug where the limit of ring travel is? If there is a ridge, how much ridge is there?

If he cannot answer those questions, go get your bike away from him. He doesn't know shit.

If there is little or no ridge at the top of the cylinders, you could probably just get away with doing rings only. That ridge indicates just how much wear there is in the cylinders. Half a thou, you can feel with your fingernail, but not with your fingertip. One thou you can fell with your fingertip. More than one thou ridge, and I would say re-bore. Less than that, re-ring only, with a VERY light honing. You don't want to remove much material prepping the cylinders.

If there are any gouges or scratches in the cylinder walls that you can feel, re-bore.

 

[frogman]

Most mechanics probably wont have the tools to tell you if it needs re-boring, a machinist (guy that does the bore job) will.

 

[hillsy]

Most mechanics probably wont have the tools to tell you if it needs re-boring, a machinist (guy that does the bore job) will.

Sorry - it's a basic part of mechanics to be able to measure tolerances like this. If you can't do that, then you're not a mechanic.

 

[frogman]

That's why I'm saying MOST. ;D

 

[crazypj]

Sorry, got to mostlyagree with frogman, most mechanics don't have a bore gauge measuring to 1/10,000" or a full set of micrometers (and lot wouldn't know how to use the tools even if they had them)
I trained as precision machinist (mainly so I could make parts fit bikes they were not designed for)
I would say a mechanic needs a 0-1" and 0-25mm micrometers to measure shims, etc, plasti-gage for plain bearings, multi meter (don't need a $200.00 one when 99% of use is volts and Ohms) plus a bunch of hand tools
As for this question, mechanic can easily make a judgement when a re-bore is necessary, machinist would need to say how big a re-bore though
A few years ago I bought several CB360 cylinder/piston sets off e-bay, all advertised as removed from good running bikes, not a single one was useable by my standards (which are not that high for mule motors)
some were rusted pretty bad one side (where valves were open)
I wasn't bothered though, did a bunch of 378cc bores last year

 

[johnny gaijin]

thanks for the info guys.

the mechanic did measure the cylinders. i don't remember what the measurement was but he said it was significant. he recommended going up two piston sizes to compensate.

anybody know a source for cl360 oversize pistons?

 

[crazypj]

Same as CB360 and a lot easier to find than GS850 pistons (for a 378cc )

 

[AlphaDogChoppers]

the mechanic did measure the cylinders. i don't remember what the measurement was but he said it was significant.

That is pretty important information to come to the forum with when asking our advice.

he recommended going up two piston sizes to compensate.

So, you would lose one whole rebuild for those cylinders.

A lot of machinists like to go two oversizes because the can bore to within 3 thou of the desired bore, and hone to size. There is micro fracturing from the boring tool, and the finish honing removes that. Trouble is, you can't really bore if going only one oversize. You have to hone only, and that makes a less precise bore. A GOOD machinist maintains his hones with a truing sleeve that corrects any taper the honing stones may have developed. This is especially true of hones used for automotive blocks. They usually only get honed from one end, and because bores wear more at the top, the hone can develop a taper. A good machinist will hone a motorcycle cylinder from both ends to keep his hone more true.

Here is some info from Tom Nichols, one of the most knowledgeable machinists I know. He has an automotive machine shop in Texas, and has done a great deal of research on the subject. This particular treatise was written in the context of Harleys, but the information is valid for pretty much all engines. I've included a link to his Web site:

"There's a ton of M&M's (myths & misinformation) floating around about how to break-in a rebuilt engine. my advice is to stop and think about what we're trying to achieve when breaking in the engine after a top-end rebuild. Basically two simple things: most important one is to microscopically lap (mate?) the piston rings to the cylinder wall. And secondly, expand/contract (heat/cool) cycle the gasket/metal interfaces (joints?).
Typically, by the time we first fire up and tune the engine, check for leaks, etc and shut it down, the gaskets/joints have expanded and contracted, and are as good as they're gonna get. So that only leaves the rings to break-in.

With today's machine shop equipment, if your machinist knows WTF he's doing, very little break-in is needed. When the jug is bored, it should be held in torque plates to simulate the clamping loads/distortion it sees when installed. (and yes, contrary to what some folks say, even Shovel jugs distort when installed & torqued) With TQ plates, the jug is bored and honed in to truer round cylindrical shape. First the jug should be bored 0.003" to 0.005" smaller than the finished size. Then honed - honing should be a three to four step process. 1st hone with a coarse grit, say 280, to withing 0.002" (If the jug is bored to within 0.003", we can skip the 280 grit step.), then hone with a 320 grit to within 0.001". Hone the last 0.001" out to finished size with 400 grit. All honing should be done with plenty of flood coolant/ honing oil. Most shops will use honing stones - they must be in good shape, parallel and not worn tapered... most hone stone sets in most shops will not be true. Ask to see their truing sleeve for the hone set if you have any doubts. At AMS, we use very expensive diamond hone sets to avoid the wear and tear that stone hones exhibit. If a shop only used one grade of stone or just hones a jug instead of boring it, its likely you'll need a L-O-N-G break-in period, as its highly likely the bore will be hour glass or barrel shaped, and not "square to the gasket surfaces. If a shop bores to size, or only leaves a 0.001 or less to hone out, chances are the micro-fracturing of the cylinder wall when the boring tool removes metal will not be completely removed, leaving tiny divots even after honing...so again a L-O-N-G break-in will be requires. At AMS, we diamond hone the last 0.003" in two steps. Why two steps? The coarser grit diamond hoen cuts cooler, so we remove the first 0.002" and most of the divots with it - to avoid heat distortion. We hone the last 0.001 with the fine diamond hone to achieve the proper Rpk, Rvk, Rk (old Ra) surface and crosshatch angle finish. Even with a fine free-cutting diamond hone, and especially with a stone hone, if you look at the "crosshatch" marks under a microscope, you'll see some jagged thin peaks. If these are left as is (as many shops do), even if the jug is thoroughly washed befoire use, these thin peaks will fold over when the rings pass over them. That increasess the break-in peroid as well. It is also why some engines will have very dirty, black oil at the first oil change after a rebuilt. In extreme cases it can even cause hi oil consumption and/or score a piston. To avoid this, AMS uses a flexhone to plateau hone the jugs. This knocks off these thin peaks and leaves a flat, mesa or plateau shaped crosshatch finish. In essence, it is a head-start on the break-in process. Lastly, AMS washes/rinses the jug in hot soapy water - this is a very important step, especially if your shop uses a stone hone. Many shops will simply wash the jug with solvent or carb cleaner or brake cleaner and wipe them out "clean". This does not remove the grit/metal particles at the bottom of the crosshatch grooves - in fact it makes it stick even more. The ionic charge of most solvents repels the grit and makes it stick tighter to the jug wall. Soapy water tends to surround the grit, its ionic charge attracts the grit and pulls it away from the wall. Read almost any ring manufacturer's installation instructions and they will suggest washing the cylinder with hot soapy water. Then oil it with clean motor oil (an exception to oiling the cylinder is some Total Seal rings).

Break-in is essentially just "scrubbing" or lapping the rings against the "rougher" crosshatch surface until both the ring and jug surfaces wear enough to microscopically seal and create a surface area large enough to support the normal combustion gas pressure load - where the psi load is supported by enough area to stabilize and nearly stop the rate of wear. How long this takes is determined by the quality of the jug bore (as described above) AND the type ring used.

Assuming your jugs were bored and honed and cleaned to today's state-of-the-art condition: rings for most Harleys fall into three categories: cast iron, steel with plasma moly face, and chromed rings.

Many older engines used cast iron rings - back in the old days these were not made as round as they are today, so they took longer to break-in. But today, they are made much better, and seat quickly. These are usually very inexpensive rings & almost goof-proof, they'll seat no matter what you do - but they don't last as long as other type rings. And if your jugs are honed wrong - they'll seat so fast they wear in and out PDQ. typically folks will think they never seated - when in fact they seated , and kept right on seating until they wore completely out in just a few hundred miles. It wasn't the ring's fault - it was either a too rich tune or a bad hone job.

Steel plasma moly rings are made to very close standards. They cost a little more, but last a lot longer. The moly cuts down on internal friction, helps mpg, and lowers oil temps. These are my favorite type of ring for Harley engines. I prefer the "2M" series Hastings rings.

Chromed rings last a long time - but that can be a bitch to seat, especially on carbed engines where the A/F mixture may not be tuned to the best ratio. The hard chrome tends to wear the jug more than the ring when seating. I do not recommend chromed top rings for HD jugs.

Steel moly rings require a bit of break-in process. The best way to seat these rings is to load the engine, intermittently, for max combustion pressure. The high gas pressure enters between the ring and upper piston land. then goes around behind the ring to force it against the cylinder wall. This speeds up the lapping/seating. It should only be done intermittently - so as to let the ring and jug remain lubed and relatively cool/undistorted from excessive heat. How you to do this? Simple - ride in stop and go traffic for about the first 200 to 300 miles. Vary the throttle - avoid steady throttle/speed/load riding. Also to keep the face of the ring and jug wall relatively cool and distortion free during break-in, we want to avoid high surface speeds between the jug and ring. So avoid revving the piss out of the engine when shifting or sustained high speed runs. Best way to do this? Ride like you're a Yankee in rural Alabama and the county-mount was followin' you <grin>.

Usually, AMS bored jugs, with 2M series Hastings rings, the rings are fully seated and broke-in after only 100 to 200 miles of this type of riding. After the first 100 to 200 miles, change the oil filter, and ride the wheels off 'er.

sorry for the long post - just trying to share a bit of info.

Respects
Tom-AMS
www.automotivemachine.com/

p.s. your machinist should also gap the rings while the jug is clamped in TQ plates."

 

[crazypj]

I've done a LOT of 883 to 1200 conversions.
Forgotten exact numbers, but, HD cylinders distort a surprising amount if honed with or without torque plates
883 has a liner about 1/2" thick so isn't a much of an issue but it's still easily measurable (in the 0.5~2 thousandths of an inch range)
Big twins (88 cu/in or more) distort further, the cylinders are quite 'flimsy'
The 'hot' and 'cold' measurements can also vary quite a lot
There are specs for minimum thickness torque plates, 'JIM'S' exceed the spec
It possible to hone 'true' I've done it multiple times with no more than 0.0002" (2/10,000") variation in taper or out of round
I've even tried deliberately tapering cylinders, tighter at the top as it expands more (wasn't 'brave' enough to try more than 0.001" though ;D )
It seemed to make a difference in finished motor but couldn't get dyno run to verify 'feel'
The Honda cylinders don't need torque plates
Hone with 400 grit and it's good for 12,000 rpm on second start, with 0.0017"piston/cylinder clearance (17/10,000")
I don't usually 'plateau finish' Honda cylinders, they use 'chrome' top ring and the sharp edges help them seat.
I do use real cheap oil for first start and change it as soon as engine is hot, (about 2~3mins)
High detergent (diesel oil) as it's mainly to make sure everything is flushed clean
Second oil change is usually around 100 miles and third around 300 total miles
BTW, fit cylinder completely dry and oil piston skirt on thrust faces below oil ring with chrome rings, if cylinder is oiled it will take several thousand miles to break in

 

[isal]

Freakin awesome info, AlphaDog. Thanks for that!