Author Topic: Ring groove clearance  (Read 804 times)

Online groily

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Re: Ring groove clearance
« Reply #15 on: 25.03. 2021 14:13 »
Jase, Happy to run through what I have done, in various stages.

I have had the bike 14 years. It was on +40s with the part number of old (which i've forgotten, but whatever was the norm back then, Swarfy etc know these things!).
After about 30,000m with me - and dunno how many if any before - I had the engine down, to deal with an end float increase on the crank.

While I was there - or at least I think it was the same visit, I only make very rare ones inside the A! - I replaced the rings, which were showing wear (oh, and exhaust valves and guides while I was on). I also replaced the big end shells while the crank was out - no wear at all there, nor on the timing side journal / bush which showed 1.5 thou clearance and was therefore good. But new shells, why not?
The cylinders themselves were also excellent still, but the pistons were  showing some signs, with skirt clearances getting towards the end. No scuffs, no nasties, just a bit of wear. Wanting to get every usable mile out of what were a good pair (because I'm a mean swine and also like bits that have run togeher to keep doing it as long as possible), I decided on 'rings only' for the time being.

After another 15K the engine was starting to get a tad noisy hot. Oil consumption modest - noticeable yes, but no smoke. Inlet valves had been excellent when checked, so I assumed probably 'Nothing to See There' then.

So, knowing the pistons were  tired last time in, after 5000 more miles I decided to see what was what. Most noise seemed to be coming from the timing cover, but all the usual suspects in there were in correct shape, and I'm belt drive on the dyn. No flop on breather, good ATD. Some possible wear on intermediate gear / cam pinion / whatever due to mileage, but nothing bad and nothing I could compare it to as I only have the one A10.

In discussing matters with Beezermacc, who knows a thing or two and does some of the same things I do, he reckoned that although the noise might mostly seem to be coming from the timing cover,  the odds were that the pistons were starting to clack about after such a mileage, and that iron head engines can apparently refer noise from pistons all over the place. Which of course tallied with where I was myself.

So apart it came.
Bores still excellent with a max wear of under 3 thou, and mostly at between 1.5 and 2, which I'm perfectly OK with. No ridge at top, no marks or funnies. As I don't want a rebore unless and until I really have to go to +60, I'd have put up with a couple of thou worse if I'd had to probably! But the pistons were now down 8 thou on skirt diameters, using the excellent data available on here for them. That was 3 thou worse than when I'd decided to keep them for the time being, so on a downhill slope, and probably accelerating towards the buffers..

The conrod eyes remained spot on for size, parallelism etc, no problems there. Head bits all still good. Even the sparking plugs, the same pair have done nearly every one of the miles I have done - B6HS NGKs - looking good for a few more years.

So it was clearly a case of 'just pistons' and nothing else.
IMDs had been recommended on here by several people, and are easily available at 7.25:1  . . . so that's what I got. +40s again.
They fitted with good skirt clearance, both cylinders, thrust faces and other sides, and no rock at tdc. Rings pre-fitted, and no need to check them, the makers' tell us. Modern oil ring looks the business.
Didn't even attack the bores with a hone, as I'm not convinced about that stuff unless things are obviously heavily glazed. New pins were a correct fit in the rods - bit of warmth, usual thing, to get everything in place - and then the  only hassle: the bloody awful circlip design, with no eyes or tangs to grab, and powerful little sods they are to squeeze too. Anyway, sorted with cursing.

Bike started first go, no smoke. Most noise gone when hot, silent cold pretty well. Oil consumption back down to 'norralot if anything' from 'bit more than I like'. Still running it gently, although without a rebore no need to be too careful I suppose. Solid copper head gasket. Checked torque (I go 34ft lbs on iron) after 200 miles, and nothing had moved at all. Brian from Oz told me they wouldn't have moved, but paranoia ruled! Rockerbox needed a tad more spannering on the four downward facing studs at the corners. Oil feed pipe banjos not leaking.

On the road, slight vibes in the 45-50mph area in top which used to be elsewhere, but not a nuisance. When I've done a few more miles it'll be back to 55-65mph at all times, where it's always been happy. And here's hoping the IMDs do as well as the old jobs, on a bike that has really been ridiculously reliable on a diet of fairly modest maintenance. I have been very lucky! Or maybe, you just can't beat the combination of LJ crank, thick-flange barrels, low compression and an iron head with the larger inlet and a 389 carb. It's supposed to be an SR according to the paperwork, but it very isn't, obviously.
Bill

Offline Minto

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Re: Ring groove clearance
« Reply #16 on: 25.03. 2021 16:48 »
Groily, thanks very much for your info and write up. I've been calling round local engine workshops to get an idea of the cost of balancing the crank but no one I've called does bikes, let alone 70 year old ones. So it will probably get built up without.
I hope that my pins fit straight in too, new bushes are cheap enough but getting someone to ream them to size might be problematic.
I use the same NGK plugs but mine are useless in no time, probably due to it burning oil. Last time I was inside I lapped the exhaust valves which seemed to help with cutting down the smoke from the left pot, but not completely cured.
Current pistons are +04 I'm going to get the bores measured by someone with better kit, skills, eyes than me as I've got wildly different results every time I've measured them. (One set of measurements reckon my bores are smaller than the pistons!!) But that was using a Vernier rather than a micrometer to measure the piston skirts, don't know whether it makes a difference. Hopefully I don't need a rebore, they look ok just a little glazed (to my untrained eyes).
I think I might replace the ex valves and guides this time around if I can find a shop to home the guides to suit, we'll see.
Again thanks for the helpful advice.
Jase
52 A10 plunger
Aprilia RSVR

Online groily

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Re: Ring groove clearance
« Reply #17 on: 25.03. 2021 18:11 »
Crank balancing can be had Jase - I have used T&L Engineering in Beds for other machines, they have good dynamic kit. I paid about 140 quid though, in 2013, for my last one, so not cheap. But, they are very very good. There's a post here somewhere with the data sheets that came with the last job (AMC twin), I think.
If your crank is standard as far as you know, (as in not had its factor altered like mikeb's) I reckon you'll be OK. I don't know much (anything!) about balance factors and so on, but BSA's used a lowish % compared to some others. Whether that gives us a bit of leeway I dunno, but whatever mine is now is 'OK' for me. Speed merchants and racing types go as far as 70% I believe for smooth high end performance. As long as you don't get the vibes at your preferred road speed - or if you change your habits - you should be OK. It's not as if we're riding around on turbine-smooth bits of kit.
If your gudgeon pins were a decent fit before, and the bushes are OK, I can't see why they'd need any attention. Mine didn't anyway, nice smooth rotation in the eyes, sticky when cold in the pistons. Over the years I've mixed and matched same-size gudgeon pins with never a problem. Sounds bad, but often isn't.
If your plugs keep fouling, then yup, could be any / all of oil, or mixture, or timing. Inlet valves might be worth looking at - a bit of wear in the guides there can do a lot of no good to oil consumption and state of combustion chamber, without necessarily making a lot of blue stuff out the back. Correct jetting through the range? And correct timing on both sides - these will all affect things. I almost never replace plugs, honestly, and the ones in the A are good despite mileage way beyond what's normal. Rusty as hell on the outside, but clean as you like on the bits that matter.
Measuring inside things is hard. I did mine, then got a mate who's a fitter and turner to use his measuring sticks, which are better than mine, and when we were agreed, I was happy. A good caliper across the bore in various spots, and an external mike big enough, is often easier than using internal mikes, or at least I find it is. Using a vernier at top or bottom of hole won't tell you a lot really, or not enough to make decisions unless they're so obvious you don't need to measure!
Valve guides might not need a lot of final fitting. But if they do need a thou off here or there, then a not too pricey expanding reamer will do it. I use them (got a cheapo box from RDG Tools I think), but care needed. Not sure of running clearances here, but on iron heads I've gone for about a thou n a half, maybe 2 (dry). Too tight is bad - been there once and won the T shirt for Git of the Year trying to be too clever by half and making things too tight.
Bill

Online RDfella

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Re: Ring groove clearance
« Reply #18 on: 25.03. 2021 18:40 »
Reaming small end bushes is not really recommended, as it's easy to cant the hole. Should be honed to size. Clearance is basically nil - gudgeon pin should just slide through. Remember, when it gets hot it will be slacker. Some engines have no clearance at all as the pins are a press fit in the rod.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Offline Minto

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Re: Ring groove clearance
« Reply #19 on: 25.03. 2021 21:27 »
Groily, thanks for your time and advice, all this is very helpful and encouraging.
Yup, I reckon it'll get built back up without any work on the crank, the subject of balance factors is just foreign to me at the moment, I need to do some serious reading around this. if it's unbearable I'll rethink and tear it down again (it'll give me a bit of time to squirrel some beer tokens away ready).
The pistons were measured by a Vernier at 90° to the pin 1/2" from the bottom, then a bore gauge with dti used in the bores, then on the locked Vernier to find the clearance. Trouble is, I seem to be putting either too much or not enough pressure on the Vernier to get a consistent measurement each time.
The bore gauge results are the same time and again.
Once the engines back together and back in the frame, I'm going to spend some time getting it all set up right, it's not really been right since I bought it 2 years ago. Misfires, drops on to one cylinder from time to time, fouls plugs at a rate of knots, smokes etc etc. Oh where to start!

RDfella
I'm hoping that the new pins will just slide in without need for reaming or honing, the only hone I have is a cylinder sized one so I'll take it to someone who knows more than me (read anyone and everyone!) and has appropriately sized kit.

Cheers
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Ring groove clearance
« Reply #20 on: 26.03. 2021 09:04 »
  Jase. The engine design carries a certain amount vibration, the severity of which varies with engine speed and the balance factor employed moves the so called sweet spot to where the machine will spend most of its running time. Replacement pistons are made to be a direct substitute, no rebalancing was ever done in the normal everyday world.

  Rough running, higher compressions, worn parts and less than adequate engine mounting are more frequent cause of vibration than a major imbalance.

 Use heat to expand pistons to allow a straight from the freezer pin to slip in. Assemble pistons onto loose rods if possible, fitting them to a built up crank carries the risk of sideways loads to the rods no matter how careful you are. Going the other way, the hot air gun gets pins out without risk of damage.

  A  micrometer is really the only way to measure pistons, at  pin height, right angles to the pin is the basic dimension. Pistons are oval, very slightly narrower measured parallel to the pin. Also top land is a smaller diameter than the rest of the piston. Folks look down the bore, see the top ring, think it's worn out!

 Swarfy.
 

Offline Minto

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Re: Ring groove clearance
« Reply #21 on: 26.03. 2021 19:20 »
Hey Swarfy, thanks for that. I've just scored a 2-3" micrometer off eBay, nice old Shardlow, just to make sure I order the right size pistons. I'm going to give the bores a light honing prior to measuring them.
But following yours and Groily's wisdom it's all getting put back together without work on the crank, unless removing the rods reveals any unexpected horrors, in which case, another rethink will be in order.
To be honest I was wondering about leaving the cases alone as they don't appear to be the source of my oil leak, ( the reason for stripping it out in the first place) but if the pistons are better fitted to the rods off the crank, it'll give me a chance to try to reseat the ball bearing in the wet sumping valve, it's not really bad but I'm sure it could be better. Oh, and I sourced a crankcase to bearing shim (oil flinger) thing to replace the one that isn't there.
Backtracking, you say the pistons should be measured at pin height, I've been measuring about 1/2" from the bottom after reading somewhere (??) to do so, kind of tricky as the current pistons are split skirt and split right where I'm trying to measure, might be why my readings have been so inconsistent, there's bound to be a little flex at that point.
I'm hoping my mic turns up swiftly, so I can get stuff ordered. In the meantime I'll strip the rest down to bear bones and measure the crank journals, I'm sure I've got a 0"-1" and a 1"-2" mic in the garage somewhere.
Thanks again
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Ring groove clearance
« Reply #22 on: 26.03. 2021 19:45 »
Jase With the crank out, grasp the nettle and get those sludge plugs out. No excuses, this is the single most important aspect of any tear down.

 Expect a nicely scored centreline on each big end shell. This is due to the sharp edge on the oil hole in the journal. Crank grinders never smooth this off and  carefully relieving the edge of the "cup" improves matters, as does widening the cup if it has been reduced by successive regrinds. This will improve the oil film distribution across the journal. Steady hand on the Dremel does it. Shells are marked as STD or  the appropriate underside, dimensions for regrinds in Service Sheet 207.  Ovality limit is 2 Thou on the Journals.

 Split skirts go to the front (non thrust side) as do the big end shell locating tabs, putting the left rod oil hole facing the flywheel. Don't rely on a previous owner's idea of what was correct.

 Swarfy.

 

Online mikeb

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Re: Ring groove clearance
« Reply #23 on: 26.03. 2021 20:38 »
jase - sorry if my references to imd piston weights and balancing increased the stress. its what i'm dealing with right now, so as they say: a problem shared is a problem doubled. in your situation I'd go with what swarfy and groily suggest.

After sludge trap, I'd also go one step further and suggest you check and re-seat the anti-wet-sumping ball (behind the plug by the timing side bush). easy when the cases are already open. Or consider the a65 mod to this (as per here: https://www.a7a10.net/forum/index.php?topic=13668.0) - I'm weighing this one up today - no-one appear to regret doing it.
New Zealand
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Offline Minto

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Re: Ring groove clearance
« Reply #24 on: 26.03. 2021 21:16 »
Mike, no worries, your input got me to start looking into the subject (dark art) of crank balancing, not something I'm going to go into just yet but very interesting. Previous understanding = 0.0
I did the sludge trap last time it was apart, less than a few hundred miles ago, but reseating the bearing in the anti wet sumping valve is going to get done ( I think it needs a bit heavier a tap with the tapping stick this time.)
Also going to look at the big end shells and measure the crank journals, it'd be rude not to while it's apart. I might even treat it to new rod bolts and nuts, who knows.
Cheers
Jase
52 A10 plunger
Aprilia RSVR

Offline Minto

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Re: Ring groove clearance
« Reply #25 on: 28.03. 2021 00:10 »
Hi Swarfy, sorry I somehow missed your last post til just.
I've been looking at the service sheet for regrind figures, it states two sets of figures, the diameter, and the other "face radius" which I'm unsure about.
Ive split the cases today and the crank is on the bench awaiting rod removal surgery tomorrow.
Do you think it's worth removing the sludge trap plugs again so soon after doing it? I've only done about 300 miles since, if that! It's just the drilling the punch marks out. It's got an aux oil filter fitted as well so I can't see there being anything in there to clean out. But if the cranks out, I suppose it'd just be daft not to.
There is no perceptible verticle movement in the rods o the rank but I can rock them slightly diagonally, if that makes sense?? Does this mean that there is ovality? Or does the ovality you mentioned refer to sectional ovality of the crank pin?
As you know this is a big steep learning curve for me, so your, and everyone else's help and patience is really very much appreciated.
Thanks again
Jase
52 A10 plunger
Aprilia RSVR

Offline Colsbeeza

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Re: Ring groove clearance
« Reply #26 on: 28.03. 2021 05:50 »
Hi Jase, Re your question regarding the sideways movement of the small end of the conrod when assembled.
I fitted new shells to a new crank last year. I have always wondered myself whether measurement of the movement indicated any significant wear down below. I still don't know *dunno*but measured both rods as a base figure.
Big end eyes were measured for ovality and next to nothing, so rods seemed OK.
I pushed the small end either way and measured the travel with a dial indicator.
I could not get perfect consistency, but measured 1.03 - 1.16mm on the Timing side, and 1.08 - 1.24mm on the Drive side.
That may be a fair guide for a new assembly, but someone else may be able to nominate maximum acceptable travel.
With big end journals and bushes on maximum wear tolerance, it may be possible to calculate the travel with a bit of geometry but I haven't done that yet.
Col
 
1961 Golden Flash
Australia

Offline Swarfcut

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Re: Ring groove clearance
« Reply #27 on: 28.03. 2021 10:37 »
 Jase. The engineering stuff is done by the men in white coats behind the big desks. All we mere mortals have to do is work to the published dimensions.

 In plain terms a crank ground to the correct size fitted with the correct bearing shells in a rod eye conforming to published dimensions and bolted up  will have the correct running clearance. This clearance will manifest itself as some sideways rock in the rods, even a small amount is magnified when you get to the small end.

 But what is important is the amount of "lift" in the big end. It should feel solid, no up and down movement at all. Any movement up and down represents wear, and in practice this gives a certain roughness to an engine, over time resulting in the  dreaded big end knock.

  From your description all is as I would expect, if it ran smoothly there is little amiss with the crank.

 As it is stripped this far, whether you examine the big ends is up to you, but with your new micrometer to hand seems a worthwhile exercise.

 I'll send a PM with more detail of what to look for.

 Swarfy.

Offline Minto

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Re: Ring groove clearance
« Reply #28 on: 28.03. 2021 13:09 »
Cheers Swarfy, I'm in the cave right now and have the rods off. Just measured the pins both look like there on their second but about ready for third grind at 1.438, but look clean and smooth, with no perceivable ovality, even with my glasses on. What is concerning me is that the face radius (is this the same as fillet radius?) looks to have been machined off!! Still there on the timing side journal.
The shells are nice n clean too.
There was no "lift in the big ends, just that bit of rock, but as you say that will have been magnified by the length of the rod.
There was no bottom end noise when it was running, just slight tapping from the timing side (gear lash??) Or maybe more likely piston slap, I've read that these old iron head machines transfer noise very effectively from one end of the motor to the other (very helpful.)
Thanks
Jase
52 A10 plunger
Aprilia RSVR

Offline Minto

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Re: Ring groove clearance
« Reply #29 on: 28.03. 2021 15:50 »
Swarfy, thanks so much for your valuable in depth pm response.
Best regards
Jase
52 A10 plunger
Aprilia RSVR