Author Topic: 750 K2 Strip & Rebuild - help please  (Read 8670 times)

Offline AshimotoK0

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Re: 750 K2 Strip & Rebuild - help please
« Reply #45 on: March 29, 2022, 04:54:21 PM »
I've talked with a few guys whose opinion I really rate and have hundreds of thousands of miles on Honda 4 engines under their belts. I still think the jury's out on this one but my gut feeling now I know the debris is probably in there but well compacted it to ideally clean it out by removing the balls (or screwed in but still staked plugs on early cranks). However I agree that if you are not going to do that then dont mess and try to soften the debris as you may soften but not remove it ..only for it to become dislodged when you run  the engin It's a pity we dont have any close up photos of the peened area post removal of the balls and also some idea of how much force it takes to pull the balls out. Nevertheless, I think I will have a go with my 750 crank simply because I have no idea of its history , other than Bryan kindly sold me it yonks ago and I think it came from a batch of engines he had....In terms of wear it's very nice though.
« Last Edit: March 29, 2022, 04:58:50 PM by AshimotoK0 »
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Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #46 on: March 29, 2022, 05:37:31 PM »
I don't think you can dissolve carbon Ash, is that true in chemistry?  Only mechanical means I've been aware of. It's essentially, the soft element grease with carbon black in it as far as logic determines.

Ordinarily something like oven cleaner, sodium hydroxide should dissolve the "fats" to release the debris and flow it out. Also in chemistry labs steam is used to remove tarring from glassware, vessels etc. Small bore probe attached to a wallpaper stripper could be used. Maybe, in the interest of science, it'll be worth steaming one or two before then removing the balls to gauge effectiveness of method Ash.

Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #47 on: March 29, 2022, 08:01:38 PM »
Well I've managed to remove the ball bearing out of a 500 crank. I'll be really honest here and say I do think this is a storm in a teacup. First off, the buildup is a grey powder, this is on a crank that's sat outside in the rain and such for some years and the buildup was still bone dry. The powder smells exactly like old burnt oil, it's just got that distinctive smell that we all recognise. The hole is 6mm and the buildup was quite solid, I didn't drill it out as that's wouldn't show how deep the powder was, so I used a small straight pick and essentially just pushed it in and turned at the same time. The powder was approx 1" deep, the gallery was completely free of powder after that. So I think what happens is that old oil collects in this pocket below the ball bearing, over time as Nigel has explained due to heat and such it just dissolves leaving the polymers, strands etc behind, this keeps collecting and is compacted due no doubt to the rotation of the crank throwing it together. However it only forms I think because this pocket is a dead end, below the journal the oil doesn't collect so it doesn't dry out and form this powder.

In short I think the powder isn't really a problem, ok if you've got the equipment yeah you can remove it but it's not going anywhere IMO. The powder is extremely fine and doesn't seem abrasive at all.

So let's hear your thoughts on this opinion.
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Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #48 on: March 29, 2022, 10:36:26 PM »
You’re possibly right Ken; I’d submerged my whole crank in a degreaser for 24 hrs - which may be the reason its collection was a paste versus powder. On the other hand, it was an active crank versus a log-time unused… could this be the issue? Given a crank normally lives in a very wet & oily environment how could a dry powder result?
Notably the remnant sludge (ex drill extraction) dissolved easily with multiple squirts of degreaser down the hole - going to almost a grey thick ink. (The crank / holes were then power washed using a high pressure hose, with compressed air blown finally blown through the galleries. You’ll forgive me Nige not suggesting Lindsay that I take it home to steam it through 😂!)
Ash, yea sorry wrt pics. Certainly not much force needed striking the balls out with the cold chisel… I’d describe it as a ‘middling’ strike. But, there was no visible damage to the holes and the new balls had to be lightly punched back in before the OEM peening holes were used a second time buttoning it all up.
The reason the buildup was in there was described due centrifugal forces, ie any small crap migrating there / into the blind alley.
As a final comment to your post Oddjob, if Honda agreed the buildup was of no consequence to the longevity of the big-ends why would they go to the additional expense of modifying the balls to grub screws?
« Last Edit: March 29, 2022, 10:41:53 PM by Lobo »

Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #49 on: March 29, 2022, 10:51:52 PM »
Who knows why Honda did things. It could be for safety reasons, maybe one of the ball bearings let go and they decided to modify it to stop that in future. You've got to admit it's a cowboy way of doing things, punch holing a ball bearing in order to keep it in place, maybe there was oil leaking past and reducing oil pressure. TBH we'll never know why they changed it, don't forget they probably didn't make the cranks, they'd have sub contracted them out, maybe they specified a grub screw instead of the ball bearing and there was no additional expense for them but for the sub contractor.

As for the paste versus powder, maybe we need another source for comparison, either way I don't think it would ever shift as there is no flow past it to cause it too move. Plus, and think about this. The oil trapped there was already filtered as it had already passed through the filter, so what exactly is the sludge/powder but dried up oil, as I said it felt non abrasive, so if it did let go and move what would if affect and where would it go, it should just dissolve into the new oil and get filtered out by the filter as it passed through. IF it felt abrasive, and I'm not saying it couldn't be, I'd be saying for gods sake remove it before it does let go. However IMO the potential for damage doesn't warrant the effort to remove it.

Just my opinion of course but I won't be doing my crank and that's done MAJOR mileage, well over 100000 miles.
« Last Edit: March 30, 2022, 02:25:25 AM by Oddjob »
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Offline Bryanj

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Re: 750 K2 Strip & Rebuild - help please
« Reply #50 on: March 30, 2022, 12:06:58 AM »
Having done more than a few Triumphs, their sludge trap gets quite full and does restrict oil flow BUT they have no filter and the trap is in line with big end pins so gets max centrifugal force. The Honda is on a blind line so theory says it will only be a problem if there is so much it fills that line.
On an asside Fiat used small core plugs to block the oilways, i rebuilt one that had knocked an end where the plug had fallen out!

Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #51 on: March 30, 2022, 09:03:10 AM »
The "Ash" content results from sulphated ash (phosphorus and sulphur) that's part of these original mineral oils and shows the oil has gone over temperature at that location. It's not abrasive, so low risk from that. This is what low SAPS oils are about now, if the oil gets into the combustion chamber it burns (over temperature same as this crank site) and forms ash which is detrimental to exhaust cleaning equipment. 
The older engine types use these components in combination with their metallurgical makeup to help stop wear.

The sludging is only from oil going over it's critical temperature AT THAT SPECIFIC LOCATION because the component is too hot if the oil there becomes slow moving. It's also seen in turbo bearings (hence the addvice to keep running a turbocharged motor after extreme heat to prevent the oil becoming stationary. Also other strategies are now more common with flow pumps after switching off and watercooled casings etc, this to prevent localised sludging. Often seen on Rover V8 in rocker cavity as the aluminium skull caps over combustion chamber eject a lot of heat that way and particularly above the exhaust ports. Notice how Honda put airflow passages throughout the head to control that effect on these sohc engines. 

I'd view the ball bearings as more gentle solution than threads to block the holes. Threads always carry more risk of propagating cracks from their form rather than a peaned ball arrangement.

I should be considered that the potential blocking with sludge can be serious in terms of oil distribution.  If the crank pathways impede the volume of oil in any significant way the pump when meeting this resistance can blow the pressure relief valve open (this is to save it's own drive mechanism from potential hydraulic locking of oil pathway) too much of this can obviously starve the crankshaft and bearings, but just as serious is the interaction of the pressure check "jets" going to the head. These must be capable of containing 60psi as that's what they do in separating the pressurized crank from the open bath camshaft area. If the oil pump pressure relief opens, it's likely that no oil will be pushed into the head while that's happening.  It'll also be worse when cold as the oil is thicker. Part of rebuilding would sensibly cover this off surely?

Offline AshimotoK0

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Re: 750 K2 Strip & Rebuild - help please
« Reply #52 on: March 30, 2022, 10:26:56 AM »
I just had a quick look in Hondman's book on the CB750 and couldn't see any mention of removing balls/plugs or  internal cleaning of the crankshaft ... surprised really and it's a very in depth book.
Unless I have missed it of course  :-[
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Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #53 on: March 30, 2022, 03:31:15 PM »

I'd view the ball bearings as more gentle solution than threads to block the holes. Threads always carry more risk of propagating cracks from their form rather than a peaned ball arrangement.

I should be considered that the potential blocking with sludge can be serious in terms of oil distribution.  If the crank pathways impede the volume of oil in any significant way the pump when meeting this resistance can blow the pressure relief valve open (this is to save it's own drive mechanism from potential hydraulic locking of oil pathway) too much of this can obviously starve the crankshaft and bearings, but just as serious is the interaction of the pressure check "jets" going to the head. These must be capable of containing 60psi as that's what they do in separating the pressurized crank from the open bath camshaft area. If the oil pump pressure relief opens, it's likely that no oil will be pushed into the head while that's happening.  It'll also be worse when cold as the oil is thicker. Part of rebuilding would sensibly cover this off surely?

I'd agree with the blocking comment IF the part being blocked was in use, the area in question is a dead end or blind gallery as Bryan puts it, no oil passes through it. As soon as this area filled after the first fire up of the engine it most likely stayed there, it's ability to drain is severely compromised by the way the shells are made, conrods shells do not have the recess in them like crank shells so they'd effectively block the gallery as soon as the engine stops, when the engines running the oil pressure would be the thing pushing the oil through the very small gap between the shell and the crank journal, I suspect the oil is far too thick even when hot to get through the same gap without pressure. That's my opinion anyway. My findings were that below the blind gallery the oilways were free of all powder/sludge. When I ran a drill down them it came back clean except for the occasional sliver of metal where it caught the side of the gallery.

As for the peened ball question, surely that can't be oil tight, the very act of peening would distort the area around the ball causing small openings, maybe the fact they are quickly blocked by the sludge/powder is a good thing otherwise you'd surely have some loss of pressure. You wouldn't get that with threads especially with thread lock used.
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Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #54 on: March 31, 2022, 08:58:21 AM »
Aren't carb galleries regularly plugged with peened balls? And if so, you’d have to assume the method as good engineering practice in terms of high performance / reliable sealing.

As a fan of ‘simple is best’ (been a LONG learning process that one 😂) I got to say I quite like the elegance of it all ….

Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #55 on: March 31, 2022, 11:43:04 AM »
Haven't looked in detail at them, but peaning will easily do this.

Regarding method though, ideally it would involve peaning round the ball in one operation.

Imagine a ball bearing that's larger than the one used in the hole, with a hole bored in itself, placed over the crank and ball assembly, then when you thump it (technical term for lumping it one  ;D ) it's own surface will compress the ring around the installed ball to pean the surrounding material in place to hold the ball and make it oil tight.

It's basic riveting really,  but with a different "snap" set to give the required metal displacement.  This stuff is pretty routine on steam boilers etc, implemented properly been holding stuff together since the industrial revolution  ;D

Guess you could call it "angular riveting" and that would certainly make your eyes water  :o

Ballls actually seal really easily,  another example is 1/4 turn ball valve in plumbing.

The issue with threads is that it cuts into the structure and makes a stress raiser all round the pointy section. Why you're unlikely to see threads cut into conrods etc.
Honda obviously okayed that though on the late cranks from observations further back.

Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #56 on: March 31, 2022, 11:59:59 AM »

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That one on the right hand side looks like the arrangement you'd need. It can't touch the ball though as you don't want to push that inwards just set the material uniformly around the ball to enclose it.


Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #57 on: March 31, 2022, 03:24:56 PM »
The cranks though Nigel are peened using 3 strike areas, well it is on the 500 crank. Seems they just used a centre punch.
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Offline Trigger

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Re: 750 K2 Strip & Rebuild - help please
« Reply #58 on: March 31, 2022, 03:28:34 PM »
You just use a center punch at 3 points  ;)

Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #59 on: March 31, 2022, 03:52:49 PM »
 :) no wonder they don't mind threading them then.

 

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