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Offline flex

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Re: Midlife Overhaul of my Africa Twin
« Reply #80 on: January 24, 2017, 02:27:42 pm »
I actually "knyped" when I saw the picture.....
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Offline NiteOwl

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Re: Midlife Overhaul of my Africa Twin
« Reply #81 on: January 26, 2017, 01:08:41 pm »
I will provide a bank account at the end of this so you can all convert your commiseration into contributions to my rebuild  fund ;-)
Meanwhile, life goes on. After two weeks in Zim I was raring to finish this.




It took another two weeks after our return before the new pump arrived; with its removal and replacement, the workshop manual recommends replacing all the related seals and O-rings (7 items in total) as well. To my mind, Honda should really include them as a kit with the pump, as BMW typically does on their car parts (can't speak for their bikes). Since Honda SA does not stock them, you have to wait for three weeks if you forget one.



It only took about 2 hours to strip off everything so carefully assembled before, until just the centre casing was left.
The two halves are held together with 5-off M8 plus 2-off M6 bolts on the LHS, and 7-off M8 plus 3-off M6 bolts on the RHS.
There are three prying points to split the engine casings, but the two dowels on my engine were a bit corroded and required some encouragement to part company. A good idea I saw on the internet was hinging two wooden battens into an X like pruning shears, and using this as a lever to open the casing through the opening for the cylinder.
The gear selector shift cam plate needs to be in Neutral for the lobes to fit through the casing as well.
Finally all is laid bare.



For the mileage on the engine, there was surprisingly little debris on the strainer (it's not accessible from outside the engine).



The wear pattern on the inside of the crank casings (red arrow) showed signs of uneven wear- resonance, perhaps? I scoured them down carefully with a Scotchbrite pad and some scouring paste. Tolerances are tight here, and the bearing surfaces are soft, while the shafts are specially hardened.



The casing is actually double-walled (how do they cast that?!), with oil pumped directly into the cavity from the oil pump via a T-tube. From there it is fed through the radial holes in the main bearings into the crankshaft and through its oil passages into the big-end bearings.



The crank, being hardened, still looked fine, but I was recommended to just clean its contact surfaces off with a scouring pad, too. The main journals in the casings still looked good too, with no obvious signs of wear.



Not the same could be said for the conrod's white metal bearings, once the muck had been cleaned out.





Detail of  bearing halves - from what I could find on the internet, this looked like erosion damage (see notes at end of post).



With all the gunge emanating from the journals, I removed the welsh plugs as recommended by Superfoxi and blasted the oil passages with carburettor cleaner. I'm not convinced that it necessary to remove the plugs as the carb cleaner's long nozzle can be pushed a long way down the oil channels, and the solvent seems to work quite well.



To make sure of the condition of the crankshaft, conrods and bearings I took the whole lot over to the engineering shop that had done the cylinders to measure everything up. They confirmed that the crank and conrods were still within spec, and that the bearings were due for replacement.

There are two codes for the casings and crankshaft interfaces to indicate which end of the tolerance range they are on. There are three viable crankpin bearing sizes and two options for the main bearings, indicated by colour codes. It's better to measure accurately to be sure that the right bearings are ordered: another three week wait to import these!



In retrospect, I could have ended up with bearing problems within a few tens of thousands of km had I not been forced to open the engine casing, so there was a silver lining to the cracked oil pump saga, after all!

There are two oil jets below the cylinder apertures, which spray oil on the inside of the pistons and cylinders. It's a good idea to clean them too. And replace two more O-rings.




Since the final drive axle's bearing can only be removed from the inside, and is exposed to a lot of strain from the long and heavy chain, it seemed logical to replace this also.
Although this bearing was still in good condition, the main shaft bearing was noisy, and the countershaft bearing alongside it had a grating sound. Sigh - another visit to Honda for parts. It seems that motorcycle bearings just aren't readily available from specialised bearing shops, apart from the wheel bearings.

The gearbox assembly has to be removed to access the final drive bearing. The three shafts can be pulled out without taking them apart. Fortunately.



Tapping out the double row final drive bearing with a socket turned out to be quite easy, and replacing it was not difficult either. No freezing required. Same for the other two ball bearings.



This was also an opportunity to see how the neutral indicator switch operates (I've always wondered): this is the spring-loaded contact ...



...which is grounded when it's aligned with the contact of the shifter drum when the gears are disengaged:



Presumably, sequential / concentric contacts are used for engines where every gear is indicated.


A WORD ON BEARINGS
A number of different bearing types are used in the engine, the choice being determined by the type of load and available space.

Since huge forces are transferred by the conrods, they require a large contact area in a confined space. Hence white metal bearings (journal bearings), which are only 1.5mm thick. The actual load is borne by a layer of lubricant forced in between the shaft and the bearing by the oil pump (this type is known as hydrostatic). This film also provides damping, a function not available from anti-friction (ball) bearings.

The camshafts, piston crown and gudgeon pins are sprayed with oil, and rely on the rotation of the shaft relative to the bearing to create a wave of lubricant between the rotating surfaces (hydrodynamic type). In the close-up photo below, you can see the plain bearing that is press-fitted in to the crown of the piston; the conrod top end is case-hardened. Both of theses interfaces are only subjected to a rocking motion with the piston movement, so there is considerably less friction wear. 

   

Needle bearings spread the load over a larger contact area (compared to ball bearings of the same size), allowing for a smaller cross section, particularly if the shaft is placed in direct contact with the needles, as done in the clutch and flywheel. This does require special hardening of the shaft, and special diamond cutters are required if you ever have to machine them.



The final drive bearing is exposed to both radial and axial forces due to the eccentric load on the drive sprocket. Deep groove double bearings are usually fitted for such applications.



I contacted a few tribologists regarding the wear pattern on the crankshaft bearings, and got this reply from Sandy Polak, consulting engineer (UK) on my enquiry:
I suspect this is cavitation erosion damage. I deduce this from the radial patterns. It looks like it has only penetrated the thin "overlay" layer.  This layer is soft and often eventually suffers cavitation damage on highly rated engines.

If it is cavitation, it could be caused by low oil pressure in the engine.  I guess that also if you are at high altitude (much of South Africa is at 1500 to 2000 m above sea level), the lower atmospheric pressure could also have a small effect on the risk of cavitation. 

The low oil pressure comment makes sense: when your engine uses oil, there are times when you run the level down low and sometimes I over-filled before long trips. This probably contributed to the wear rate, even though my oil pressure light never came on whilst riding.
Do it before you die!
 

Offline Sam

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Re: Midlife Overhaul of my Africa Twin
« Reply #82 on: January 26, 2017, 05:20:55 pm »
Wow - amazing how much scunge there was on those big-ends!

Also amazing to see how short / narrow that crank actually is.

Thanks for the detail.
 

Offline Sam

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Re: Midlife Overhaul of my Africa Twin
« Reply #83 on: January 27, 2017, 09:29:31 am »
As a matter of interest, how often did you do oil changes? ie how many km between changes?

Also, what type of bearing are the main bearings? Rollers or white metal?
 

Offline flex

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Re: Midlife Overhaul of my Africa Twin
« Reply #84 on: January 27, 2017, 09:36:46 am »
Never seen muck like that in a big end ?
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Offline NiteOwl

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Re: Midlife Overhaul of my Africa Twin
« Reply #85 on: February 02, 2017, 12:44:00 am »
As a matter of interest, how often did you do oil changes? ie how many km between changes?

Also, what type of bearing are the main bearings? Rollers or white metal?

Oil changes always before a trip; usually between 6000 and 7000 km. More on this later.

There are no anti-friction (ball/ roller type) bearings on the cranks or pistons. I think the conrod big ends are white metal (in steel backing plates) while the crank ends could be tri-metal (golden colour).
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Offline NiteOwl

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Re: Midlife Overhaul of my Africa Twin
« Reply #86 on: February 02, 2017, 01:21:05 am »
Once all the internal seals and bearings mentioned previously had arrived, the engine reassembly could finally commence. External parts are less of an issue, as they can always be serviced without the need for major disassembly.

The first step should have been to refit the welsh plugs in the crank (nearly forgot those!) and punch the rim again to secure them.



There is plenty of depth to accommodate the plugs.



Here are the new conrod bearings. The two halves are identical, so you need four of them. They can be slid in and out of the housing bore sideways away from the locating  tang; the alignment of the ends is important for the "crush" of the bearings, which ensures a snug fit to minimise bearing movement at the specified torque..

 

The two bearing halves are fitted with the locating tangs facing each other (arrows). Note the pale green marking which is the thickness code.



The green colour code is rather inconspicuous. Note the slight overhang on the left hand side (for the crush).
The fastening torque is a considerable 42 N-m, and probably critical to achieve a Goldilocks fit.

So here are all the parts in the correct locations of the two crankcase halves.



Prior to locking all of this up, it's worth doing a trial fit. With my recent experience, forcing it is not advisable.



I couldn't get the casings to fit together again. It's difficult to find out why, because you can't see inside! There were two reasons:
1. Corrosion on the dowels, which needed some sanding and lubing
2. The oil feed T-piece from the oil pump to the crankshaft cavities did not line up; turning it around and smoothing the tube end sorted that out.



Once everything fits, it's a good idea to check gear the changing mechanism. No problems there, just a bit hard to rotate the shifting drum by hand.
I marked the fasteners after torqueing them, to keep track and as photographic reference,



Preparing for the reassembly requires clean crankcase faces: I scoured with a Scotchbrite pad and mixed off with meths.



The next trick is to lubricate all the working interfaces in the LHS case without wetting the mating faces. I mixed a bit of lithium grease with motor oil for this.
The sealant for the casings needs to be applied sparingly to the RHS, to avoid getting it into bearings. It needs to be done quickly, as it cures rapidly.



I think I got the correct amount of beading on the outside and inside of the splitline on my second attempt.



The Permatex instructions advise hand-tightening all the bolts and leaving it for an hour before torqueing to spec.
Once that is done, the pistons can be refitted on the conrods, after which the cylinders are slid in position (I'm sure there is a trick to it, but I found this quite difficult, as care is required to avoid damaging the rings).
 


Once the pistons were in, I checked for smooth movement and even spread of the oil around the cylinders when turning the crank. Looks good to me! Note that the pistons have an indentation on the exhaust valve side.



After refitting the cam chains, flywheel, clutch and heads, I was finally back at setting the timing. Best to make sure that all is well before fitting the engine back into the frame. No drama with the water pump this time- lesson learnt.



I considered the suggestion to lay the bike on its side for refitting the engine, but opted to call Eddie over instead!
Basic problem: the engine weighs 60-odd kg, and is difficult to handle, plus most off the mounting bolts slide in from the closed frame side (LHS). SO they cannot be inserted with the bike on its side.
So, more ropes, plus the bike stand to take the weight of the engine.



The trick is to get it in at a tilt, parallel to the frame, heads first, and then rotate the crankcase in.

Once the engine is supported by the frame, it's a good time to fill up the oil and check for leaks before re-installing everything.
I connected up the starter motor without the sparkplugs and cranked the motor. A good check is the time it takes for the oil pressure light to go out (after starting to crank) and how long it stays off once cranking has stopped.
Once the coolant hoses and radiators are refitted, the same check can be done for the coolant.



Ready to fit the carbs... I did find the routing of the myriad venting and draining hoses quite tricky, even with the pics I took during the disassembly.
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Offline 1ougat

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Re: Midlife Overhaul of my Africa Twin
« Reply #87 on: February 02, 2017, 07:36:48 am »
Think you caught it just in time - engine was on its way om "bearings te slaan " with all that muck - maybe wrong oil ? or is this normal ? but I doubt that
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Offline NiteOwl

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Re: Midlife Overhaul of my Africa Twin
« Reply #88 on: March 20, 2017, 11:39:54 pm »
ELECTRICS

The only chapter in my workshop manual that was untouched after rebuilding the engine was the starter motor. It’s never given any trouble, but while everything was exposed, it seemed logical to take a closer look at that too.
 


The brushes can be replaced when they are worn below their 6mm limit, but mine had hardly any measurable wear.



There are a number of washers and a shim on the opposite side. And another O-ring, which I replaced, too.



The rotor runs in roller bearings at the drive end, and a bush on the side where the brushes are (possibly because of the carbon deposits from the brushes).

The outer casing was quite dirty and a bit corroded. After some brushing and scouring, it looked much better, but that bare metal would need some protection again.



Unfortunately, zinc (re)plating of the steel casing (the end parts are cast aluminium) is not really feasible- the pole pieces are bonded to the casing.

The simplest solution is therefore to paint it. I mixed up some more of my remaining 2K paint and got the bolts re-zinced (just the natural finish, without the yellow chrome treatment afterwards) together with all the engine mounting bolts, which could do with some cleaning up.



Almost like new again!


The OEM fuel pump is another aspect of the Africa Twin that causes many owners to replace it with a Facet pump. The Facet pumps work, but have to be shoehorned into the frame. For one, the outlet is opposite the inlet, instead of adjacent to it.



I rather prefer the original design as it is easy to inspect and quite reliable except for the wear of the electrical contacts, which can be cleaned in the field unless the contacts are REALLY worn. They can also be replaced with a new contact kit from WEMOTO for about GBP 20.



So why does this wear happen? The reason is the energy that is stored in the windings of the pump (effectively, this is an inductor) from the current flowing  through it while the contacts are closed. When the contacts are opened, this stored energy tries to counteract the interruption of the current through an effect called "reverse Electro-Motive Force". The reverse EMF can result in voltages much higher than the battery voltage across the contacts, as can be seen on the oscilloscope image below.



The vertical scale is 10 Volt/division, so we have a peak of more than 50V when the contacts open, which happens every 25 milliseconds (5 ms/div on horizontal axis) or at 40 Hz. This voltage ionises the air between the contacts, resulting in arcing.

Of course, it would be better if no replacement of the contacts was needed. This requires protection of the electrical contacts; either by absorbing the energy stored in the windings of the pump, or by using a solid state switching element to carry the current for the solenoid (controlled by the contacts). It's also possible to fit a capacitor across the contacts (as done for the points in older ignition systems) to absorb the energy, but the capacitor will be discharged when the contacts close again, increasing the current through the contacts. On a practical note, the size of such an additional component is a problem- it will have to be fitted outside the pump housing.



Since diodes of the appropriate voltage and current ratings are fairly small (about 5mm diameter by 10mm body length) it is feasible to mount one inside the dome of the fuel pump, next to the contacts. A bit of silicon sealant provides mechanical support. The effect on the reverse EMF is obvious: less than 14 V and no more spikes. The cycle time and duty cycle is increased, but should not have any detrimental effect.

The arcing across the contacts is now negligible and the protected contacts should last a very long time- start the clock!
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Offline 1ougat

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Re: Midlife Overhaul of my Africa Twin
« Reply #89 on: March 21, 2017, 06:54:16 pm »
Did you use a Zenner or Avalanche diode ?
Make mine a Boxer with a shaft!!!!
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Offline Herklaas

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Re: Midlife Overhaul of my Africa Twin
« Reply #90 on: March 21, 2017, 07:52:42 pm »
 :sip: I see very little carbon from the brushes in that cup, unusual for a bike that age, must be good quality, seeing that I had to replace my bikes starter at 29 000
with the brushes gone.
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