Boxerworks.com

SteveD wrote: ↑Mon Jun 20, 2022 7:42 am apologies to kmisterk for a classic boxerworks thread takeover...
gspd, I'm discussing 2 cranks here.
1. it was sent away to be sorted, re grind etc.after it developed a bad knock.
2. is the one pictured. It came out of an engine that was part of a bunch of boxes of parts.
I've updated the thread I had about the parts bike gspd...so the details are on there.

gspd wrote: ↑Sat Jun 18, 2022 9:24 am

Rob Frankham wrote: ↑Sat Jun 18, 2022 5:07 am ....it's a bad idea to source new bearing shells until you know the state of the engine...

We absolutely agree on that...
I initially said: "I would tear it down for an accurate complete diagnosis before investing one red cent."
kmisterk found this impractical given his situation.

Rob Frankham wrote: ↑Sat Jun 18, 2022 5:07 am Suffice it to say that I have known a number of reground cranks go on to give perfectly good service for years.

Where we disagree is that I say "NOBODY on the planet can PROPERLY regrind these cranks".
And that's without even factoring the cost vs. a new one.
You say it can be done but can't provide a link to someone who has a good track record of doing it.
A long time ago (pre-internet) our BMW Canada service rep inquired directly to the BMW factory division where the cranks were made to see if they could regrind a few cranks for us. The factory manager's response was "Our business is to fabricate and sell new parts, not to repair old ones".
Over the years a few independent shops invested in what they thought was needed to do the job. They all quit doing it after repeated (and almost instantaneous) failures.

All repair shops will polish up a lightly worn or lightly blued crank, install new stock sized bearings and shells and call it a 'bottom end rebuild'. And there's absolutely nothing wrong with that. That's the way to do it. These 'rebuilds' will usually run 'virtually' forever. Just don't confuse this job with a regrind with oversize bearings and shells of a severely damaged crank. Some shops will say "Sure we can do anything, send us your crank" only to call you back a few weeks later and say " Sorry, your crank is just too worn/damaged to regrind, you'll need to buy a new one." By then your on the hook.

BTW RobF- You still didn't answer my question...
Can you provide a link to one of these airhead type 247 crank regrind 'experts'?
Can anybody?

jackonz wrote: ↑Fri Jun 24, 2022 12:36 am

gspd wrote: ↑Sat Jun 18, 2022 9:24 am

Rob Frankham wrote: ↑Sat Jun 18, 2022 5:07 am ....it's a bad idea to source new bearing shells until you know the state of the engine...

We absolutely agree on that...
I initially said: "I would tear it down for an accurate complete diagnosis before investing one red cent."
kmisterk found this impractical given his situation.

Rob Frankham wrote: ↑Sat Jun 18, 2022 5:07 am Suffice it to say that I have known a number of reground cranks go on to give perfectly good service for years.

Where we disagree is that I say "NOBODY on the planet can PROPERLY regrind these cranks".
And that's without even factoring the cost vs. a new one.
You say it can be done but can't provide a link to someone who has a good track record of doing it.
A long time ago (pre-internet) our BMW Canada service rep inquired directly to the BMW factory division where the cranks were made to see if they could regrind a few cranks for us. The factory manager's response was "Our business is to fabricate and sell new parts, not to repair old ones".
Over the years a few independent shops invested in what they thought was needed to do the job. They all quit doing it after repeated (and almost instantaneous) failures.

All repair shops will polish up a lightly worn or lightly blued crank, install new stock sized bearings and shells and call it a 'bottom end rebuild'. And there's absolutely nothing wrong with that. That's the way to do it. These 'rebuilds' will usually run 'virtually' forever. Just don't confuse this job with a regrind with oversize bearings and shells of a severely damaged crank. Some shops will say "Sure we can do anything, send us your crank" only to call you back a few weeks later and say " Sorry, your crank is just too worn/damaged to regrind, you'll need to buy a new one." By then your on the hook.

BTW RobF- You still didn't answer my question...
Can you provide a link to one of these airhead type 247 crank regrind 'experts'?
Can anybody?

All you need to do prior to getting a crank regrind is establish if you can get bearing shells under-size to perform a regrind and that the crank is not too far worn for the grind, second is taking it to a reputable engine re conditioner shop who have a good crank grinder and operator, in the shop I used to work in (now closed down) you could do a book grind and that means simply grinding the journals to the next nominal size in the manual, or and this is the best method a measure and grind, this entails fitting the bearings to the rods measuring them at the vertical oil clearance point and then grind to the specified clearance.

Note and this is important that if you ever get a big end knock to check that the big end bore in the connecting rod is still round and correct size (bearing shells out cap on and tightened) if not get it re sized or you will have a bearing failure real quick. I've seem many people re build a motor with a re ground crank only to have it fail for this very reason.

Note there is no such thing as oversized bearing for a regrind of the crank journals they are all termed under size as you are grinding the crank to the next under size, there are some engines as in the old VW air cooled engines where you can get over size backs with under size for the crank and this entails line boring the crankcases for the shells to fit, some D Series ford Diesel engines had over size backs from the factory and they were +15 thousands.

My advise to anyone building a motor no matter what make or type measure everything before you start assembling and check its all within specification, if you don't know how find a friend who can help.

Rob Frankham wrote: ↑Fri Jun 24, 2022 4:41 am Note there is no such thing as oversized bearing for a regrind of the crank journals they are all termed under size as you are grinding the crank to the next under size, there are some engines as in the old VW air cooled engines where you can get over size backs with under size for the crank and this entails line boring the crankcases for the shells to fit, some D Series ford Diesel engines had over size backs from the factory and they were +15 thousands.
As has been mentioned, there is an issue with the balance weights on airhead cranks. They have to be removed for grinding to take place and few shops have the necessary equipment to replace them with guaranteed security. Buying the equipment for the low volume of use it would get isn't cost effective. This is why many engine shops won't even contemplate grinding an airhead crank. With the balance weights off though, regrinding is quite straightforward. As an aside, I've often wondered how a 247 series engine would run without the balance weights... but not enough to try it...

gspd wrote: ↑Mon Jun 20, 2022 12:27 am

Kurt in S.A. wrote: ↑Sun Jun 19, 2022 1:44 pm I always thought that the names of Chris Chambers, Joe Groeger, and Ed Korn and possibly Dan at Cycleworks were capable of regrinding cranks.

Thanks Kurt, I emailed them for info, awaiting a response, but I'm pretty sure they only do /2 cranks. I'll report back when I get an answer.

SteveD wrote: ↑Sun Jun 19, 2022 10:46 pm My engine wasn't rebuilt by me. The local guys at BM Motorcycles in Ringwood, Victoria, Oz did the work. They sent it out to a place in Sth Oz. I don't know that place but I do remember asking if repair was wise. They were very confident.

So I guess there's no way to know for sure if it was actually reground and fitted with oversized bearings. Maybe it was, maybe it wasn't. I hope it lasts forever for you. The only way to really know is if something goes wrong, otherwise there is no reason to take it apart.

SteveD wrote: ↑Sun Jun 19, 2022 10:46 pm That picture of my spare crank is after I polished it slightly. It looked ok so I had it professionally measured to be sure. I can't remember if that pic is before or after the inspection.

I guess there's nothing wrong with having it professionally measured, but just for the record, if you know what to look for, and it looks that good, it IS that good. A bad crank just can't look that good.
"You don't have to be a weatherman to know which way the wind blows". - Bob Dylan

RANT (does anybody actually read this shit?)
I was taught by more than one of my bosses that smoke and mirrors is a HUGE part of doing business, it's part of "the customer experience". For example, a client walks in with a box of parts and pulls out a cylinder he would like inspected. He wants to know if he needs a new one. At first glance you notice a 1/8th inch ridge at the top, a few very deep rusty scrapes, all the original honing marks are totally worn away, and there are visible signs of a partial seizure.
Don't immediately tell him it's scrap.
Instead, wipe off the counter, pull out the fancy velvet lined bore gauge box loaded with its shiny precision tools from the top shelf in the office, wipe the cylinder down with some brake cleaner and a clean shop rag, carefully take a dozen measurements of the cylinder in different directions, top, center and bottom of the bore while meticulously writing each one down. Then, pull out the 'big book' shop manual, and after a bit of page flipping, pull up the spec sheet and ramble off some numbers to the customer, who is now looking at you like you're Einstein. To add icing to the cake, do some simulated math on a piece of paper for a few minutes.
THEN, and only THEN, tell him it's scrap.
Customers love that kind of service.
The bonus is that if the customer choses not to buy a new cylinder from you, or chooses to buy one elsewhere, you can charge him something for your 'inspection' time.

gspd wrote: ↑Fri Jun 24, 2022 5:58 am

Rob Frankham wrote: ↑Fri Jun 24, 2022 4:41 am Note there is no such thing as oversized bearing for a regrind of the crank journals they are all termed under size as you are grinding the crank to the next under size, there are some engines as in the old VW air cooled engines where you can get over size backs with under size for the crank and this entails line boring the crankcases for the shells to fit, some D Series ford Diesel engines had over size backs from the factory and they were +15 thousands.
As has been mentioned, there is an issue with the balance weights on airhead cranks. They have to be removed for grinding to take place and few shops have the necessary equipment to replace them with guaranteed security. Buying the equipment for the low volume of use it would get isn't cost effective. This is why many engine shops won't even contemplate grinding an airhead crank. With the balance weights off though, regrinding is quite straightforward. As an aside, I've often wondered how a 247 series engine would run without the balance weights... but not enough to try it...

Lineboring is a common practice in engine rebuilding.
Type 247's are a breed apart. Balance weights are one definite issue, but so is the fact that the 247 cranks are so short. You need some custom precision made spacers to make it long enough to fit the machine. As far as running one with no counter weights, it would be an interesting experiment. IMHO, seeing that there is no center bearing between the left and right throws, I would predict that the intense vibration (from no counter weights) would cause it to snap like a twig almost instantly. I'd like to see that, so if you ever try it, be sure to youtube it for me.
PS. In the industry, replacement bearings that are thicker than standard whether to compensate for crank grinding or case boring are all referred to as 'oversize', even though their I.D. can be smaller.

Not sure where you get the idea that you would need spacers to fit a short crankshaft in a crank grinding machine as none are required at all, all crank grinders have movable heads at each end with one being the drive, each end also has balance weights so that the crank no matter what size is balanced and spins at a constant speed, next is the issue of no centre bearing it makes no difference whatsoever when your grinding a big end journal the chucks at each end of the machine are set to half of the stroke of the engine from the centre, this then has the journal spinning to the centre of the machine and the rest of the crank running off centre, first time you do this it can feel quite odd and some people cannot get used to it at all, once you bring the grinding wheel in you have a steady that supports the journal from both the bottom and also 180deg from the grinding wheel, you take a small grind to clean up the journal back off and measure, when you continue the machining you then have what is termed a flying micrometer this is a dial gauge and you set it to monitor what you need to machine down to and that's it, you do the same on all the journals, when it comes to the mains its easier as they are all in line and run centre.

As I have not had one of these cranks out yet and not seen first hand how the balance weights are secured I cannot comment, however it would not be the first time iv'e seen a crank with this arrangement and removed them for machining so I doubt it's impossible.

Sadly worldwide it seems reconditioning engines with the exception of large Diesel Motors is becoming less common and finding quality machine shops the same, here in NZ in the city where I reside there used to be 3 workshops now only one.

I'm leaving for a long awaited (and disconnected) 4000km ride now, back next week.
You're in charge (Rob F) so be good.