Topic: Sandcast Engine #1770 rebuild - it made it!

[MauiK3]

You of course have new shifter spline?

[HondaMan]

Interesting.....
I'll have to open the clutch in the K0 spare motor I acquired

You can see it by just removing the engine's clutch cover: if yours is one of the un-holey ones it will be plain to see.

[HondaMan]

You of course have new shifter spline?

Well, I have a better one, from a K1 engine. It appears to be very much the same, except the spring on the sandcast version is much stronger, so I'll first just swap those. The K0's shifter drum detent mechanisms are different from the K1 and later versions, and more of a nuisance to assemble, with a double bend-tab lock plate for the detent arms' and the birdcage's nuts. The later engines just used lockwashers.

One mystery item still: the shifter-side engine cover is not among the parts in the boxes that came with the engine. And, a carefully-made sleeve was found slipped onto the shifter arm's pivot that would go into the side cover's hole (where the seal lives on the outside). I suspect that the owner was trying to "reduce the friction" of the shifter arm's pivot, and may have tried boring the hole in the side cover out a little bit and then, by installing this sleeve on the outer part of the shaft, make a bearing of sorts.

Or...it may have wallowed out that shifter-shaft hole so much from the high torque of trying to shift a recalcitrant gearbox that the seal couldn't stay wrapped around the shifter shaft, so it leaked a lot, and this was his 'fix'?

Either way, the splines being so twisted up tells an unhappy story, for sure.

[leovich]

Today's holdup: awaiting some sort of response (still) from CMS about when (or if?) they will ship the grooved output shaft's outer bearing I ordered last week, no news from them yet about it. I hope I don't have to make one, that will be expensive!

I also ordered the inside parts of the final-drive shaft's chain oiler. The K0 versions had 3 little pieces inside: it was essentially a sponge-like plug with rubber seals that slowed the oil from the little pan inside the engine from reaching the hole(s) on the final-drive shaft. The K0 was renown for its oily mess here, though, which generated the later adjustable versions: this one was essentially a medium or large leak. In this engine, all those parts are gone, so without SOMETHING inside this shaft it will drool oil all the time, yuk.

I also had to order the larger outboard primary sprocket's bearing, as I only have some used grooved ones around here. This one is not grooved (but at least is a common 6008 bearing!).

Can I suggest the upgraded adjustable version of this chain oiler Honda made to directly fit on K0 and sandcast? You can find some on sale online, I mean you can find complete chain oiler kits to directly replace the leaker original one with the felt sponge that is impossible to set.
As it is a Honda factory upgrade part I think it is the better solution, email me if you want some links for that kit

[HondaMan]

Today's holdup: awaiting some sort of response (still) from CMS about when (or if?) they will ship the grooved output shaft's outer bearing I ordered last week, no news from them yet about it. I hope I don't have to make one, that will be expensive!

I also ordered the inside parts of the final-drive shaft's chain oiler. The K0 versions had 3 little pieces inside: it was essentially a sponge-like plug with rubber seals that slowed the oil from the little pan inside the engine from reaching the hole(s) on the final-drive shaft. The K0 was renown for its oily mess here, though, which generated the later adjustable versions: this one was essentially a medium or large leak. In this engine, all those parts are gone, so without SOMETHING inside this shaft it will drool oil all the time, yuk.

I also had to order the larger outboard primary sprocket's bearing, as I only have some used grooved ones around here. This one is not grooved (but at least is a common 6008 bearing!).

Can I suggest the upgraded adjustable version of this chain oiler Honda made to directly fit on K0 and sandcast? You can find some on sale online, I mean you can find complete chain oiler kits to directly replace the leaker original one with the felt sponge that is impossible to set.
As it is a Honda factory upgrade part I think it is the better solution, email me if you want some links for that kit

Thanks for the tip! I would like those links: I have another K0 engine in the [slow] works, and someone stole the chain luber parts out of its drive shaft before I got the engine. It's missing many other parts, but someday I'll have enough to put it all together again.

I talked with the owner: he'd prefer the pan just remain gone (as it is now) as as to save adding racing stripes to his jacket.
I can't really blame him: I turned mine off years ago as we have some real good chain lubes today that cling and lube well. Mine is turned down so far that it doesn't start letting oil out until about 60 MPH: that's about what will happen when the pan is removed and the passages left open.

[HondaMan]

Today's progress, in between painting the parts of another engine in-process, was to reassemble the clutch sandcast style. This one is a 7-plate clutch without the little wire retainers I've found in other similar engines and some K1 (including my own). Instead it has the first version of the "clutch plate lifter" ring that is supposed to help shake loose the 2 top plates when the clutch is pulled in. It didn't work quite as planned at the time, but that was due to lack of oil available to slip in between the plates to break the friction as the Lifter Ring was trying to shake them apart. With the added oil from the mainshaft hole now being normal size and the hub oil distribution slots opened up like in a K4, this one should actually work, now.

If you find an engine with this Lifting Ring, it goes in between the 2nd and 3rd  clutch friction plates, over the steel plate. Some of the K0 clutches had just 6 plate pairs instead of 7: it still goes into the 2nd position on those, too. The right-angle inner fingers point out, away from the engine, and they go in the same slots at the outer fingers of the friction plates - not in the curved recesses in the clutch outer fingers.

[HondaMan]

After applying Hondabond to the cases and closing/bolting them, I opened it back up to check the seal all around with all the bearings installed, just in case a warp may be hiding somewhere. It all checked out good! There's just one more hole that needs to be aligned, drilled and tapped: the sprocket-side rear engine boss that clamps the final-drive bearing in place (that I had the welder build back on for me) needs to be drilled/tapped in the exact center.

Then, on to the top end!

[grcamna2]

The installed cylinder studs:are they OEM Honda for the sandcast ?

[HondaMan]

The installed cylinder studs:are they OEM Honda for the sandcast ?

Yep! They work fine, so long as the O-rings in the head gasket are made 2.6mm thick with the modern head gaskets.

[HondaMan]

OK: I have oil pump rebuild pix next, those will take a while to post, though.
In the meantime: the Sandcast (and many early K0) heads had a very poor oil-metering scheme for the cam and rockers, which is why so many of them are now found with non-original top-end parts. The oiling hole was a 0.040" (0.1mm) hole drilled from the inboard 2 head studs thru to the bottom of the cam bearings, and this hole was more than 1/2" long. As with any fluid dynamics analysis, this meant that the intended flow, which was to be set by the 0.1mm/0.040" hole size, was going to be a LOT less than intended, and when cold, almost none. Without boring everyone with the engineering math, what this results in is this:

-When the engine is cold, around 10% of the desired oil will flow to the top end.
-When the engine is hot, only around 40% of the anticipated flow will reach the top end.

Now...fluid dynamics clearly tells us that the longer a tube is, the more the restriction is in that tube. You can figure this stuff out yourself with a 5-gallon bucket and a garden hose: put a 1/4" tube in a hose-end fitting, make it 5x that length (1.25") and time the fill of the bucket at full pressure: then cut off the 1/4" tube so the length of the hole is just 1/4" long (i.e., same length and diameter) and fill the bucket again: you'll find the second bucket filled up much faster. The time difference will let you figure out the increased flowrate from the "shorter" hole if you're quick with math.

In these heads, the metering holes in the normal oil jets (both domed and machined types) are 0.0375".0.095mm. In the late K7 and the K8 engines this was opened up to 0.040"/0.10mm. But, the length of the "tube" in the oil jets is only 1mm/0.040", so the flow is much closer to the Engineer's anticipated flow rate. By simply drilling a long 0.0375"/0.095mm hole thru the head to the stud (which was the early practice), the length of that hole severely restricted the oil flow by effectively making the hole smaller - much smaller. The result was the [in]famous loss of cams and rockers, and those rocker shafts, in the sandcast and K0 engines. Honda kept changing this design: I have more than 5 instances of the changes and the many mods that came out for them, and almost all of those, save one, could have been avoided.

Here's a sketch to show you how to mod one of these early heads, as I just finished, to make it last. Just run a larger drill (0.060" to 0.065" will do) into the metering hole from above, stopping about 1-2mm short of going all the way thru.

Now, this all said: a few years ago I rebuilt and engine for a rider who flew from California to Michigan, bought a (beautiful) 750K5, then rode it back to California, stopping here enroute to have me install a Transistor Ignition. When he got home he tore the bike down for a complete resto, and sent me the engine for a rebuild to go with it all. When i pulled off the rocker towers, there were NO oil jets in the stud holes: whoever was inside the engine before me left them out during reassembly. This did no harm to the engine's bottom end: the crank and rod bearings were in fine shape and the cam and rockers looked new. There were no issues with shifting nor speed problems on the rider's trip, either, and he ran at 75-80 MPH the whole way.

So, making the oiling holes MUCH bigger then causes the other holes (2 in the back of the rocker towers and 2 in the cam bearings of each one) to become the metering holes, and the oil pump is obviously well-suited to run with that much flow. These other holes are all 0.040"/0.1mm or larger, too. In this engine I left the inner hole at the original spec of 0.040"/0.1mm (as measured) so it will be metering the same flow as the later-style oil jets. This shouldn't affect the 'value' of the sandcast engine, but will make it last much longer.

[HondaMan]

My next interesting item: I've not seen this before in a 750 engine, maybe one of you out there has?
The shifter shaft has a collar that slips onto the shaft. This collar mates with a PHENOLIC bearing that was inserted into the shifter case for this shaft.
Did Honda do it? Dunno...never seen this before!

It's no secret that shifting the sandcasts and early K0 engines was often a PITA. The oil metering hole in their mainshafts (see above posts for that mod) were much too small - matching the sizes found in bikes like the CB160, which was the most-similar clutch to this one - making for too-dry clutches that wore out their plates quickly. IIRC there are 4 different K0 clutch arrangements, which were:

1. This one, which has the too-small mainshaft oiling hole and no oiling holes in the inner clutch hub for the plates.
2. The 2 inner steel plates were held in place with 2 steel wires that mounted thru 2 holes in the inner hub, much as in the CB160 and other engines.
3. The loose steel "lifter ring" (like this one has, see posts above) that was there to shake loose the 2 top cork plates when the clutch was pulled. (This version sometimes also had the 2 steel wires holding the back steel plates in place.)
4. The inner hub had oil holes in it to lube the cork plates better than "by osmosis", or whatever that Clutch Engineer had deemed was happening.

Personally, I think all of them before the holes in the inner hub were done by someone who enjoyed too much saki and was too well-connected to lose his position as Designer...these various clutch arrangements kept reappearing in later engines, too, because of the practice of 'recycling' a defective engine, as found during one inspection or another, which pushed the engine back into the shop for corrective action before it went to the Production Line. My first 750 was a K1 built in 4/71, and it had the clutch hub with the 2 wires in it to hold the rear steel plates in place: my [present] K2 also had these when I first got it, and it obviously has a recycled K1 engine in it, from the Old Factory. It doesn't have those anymore, and has a later hub in it now, with enhanced oil holes and sipes, as shown in my book (and pix above). The only issue with those wires is: in city traffic on a hot day when the oil is getting thin, the inner 2 plates will not release well during a 2-1 or 3-2 downshift unless the throttle is simultaneously 'blipped' while the clutch is pulled. I have noticed when riding even now that I still do this (unconsciously) after all the years of doing it with both my 750s, and I tend to do it when riding other bikes, so I guess old habits die hard?

[BenelliSEI]

Wish I’d seen your sketch above, before I put mine back together…….

[HondaMan]

Wish I’d seen your sketch above, before I put mine back together…….

Uh-oh, sorry!  :'(
I think the lore of the sandcast is a lot like the lore of the M1911: more has been forgotten than remembered. You can build a functioning unit with the typical manuals, but making them smooth and take-all-comers reliable sometimes needs ... an old guy?

This mod can be accomplished with the engine in the frame: it's painful, though. All the pipes, airbox, and all the engine mount bolts but the lower rear one come out to drop the engine down far enough to remove the cam cover and all that top end 'stuff' to get to the 2 inner rear head nuts. Then those get removed, a [plastic or cardboard] tube slid down into the stud holes to stop any debris falling down inside, then the 2 tiny oil holes get drilled just short of 1/2" with first a 0.055" drill bit (by hand and pin vise), followed by the 0.063" bit until you feel it hit the step in the holes. Then you just clean it all out of chips (they collect in the recess where the O-ring lives) and put it all back together(!). It's been done (in Illinois), not by me, though. More often, the holes were just drilled thru with the 1/16" bit they bought at the local hardware store, with the engine out anyway because the cam bearings were all torn up.

It would also help if some certain parts were still available somewhere - like proper head gaskets.

[HondaMan]

Started putting the head on and discovered the RH sealing bolt's holes had no threads(!). A 6mm Helicoil fixed that up.

Then came sealant apply, since the front of the gasket at the camchain tunnel will need some assistance to stay dry: no one offers the old-style head gaskets with the un-holey front center strap now.

With head gasket and oversized oil port O-rings in place, head goes back on.
This might run yet!

[HondaMan]

I discovered the 4 6x35mm crosspoint head sealing bolts are missing from the bags of screws, so I had to use some normal 6x35mm flanged bolts instead. The only way to tighten the outer 2 of these is thru the fins if there's no crosspoint, using a thin 10mm wrench. This arrangement remained until the K4-style head came out in late 1973.
(Film at 11...)

[HondaMan]

The Oil Pump refurbish consists of replacing the inner shaft seal between the 2 chambers and the O-rings inside the chamber covers.
This seal gets PUSHED in using the ballpeen hammer face, no pounding, please...
The covers go on and the screws get snugged and the gear turned alternately until they align and the screws are tight, then a whack with the impact driver and final check to make sure the rotors spin easily. a hint: make sure the rotor punch marks are both on the same side if the rotors are pristine: if they are worn then sometimes flipping one will help with reassembly and alignment, and pump performance is the pressure was low.
The pressure-relief valve was cleaned out and the checkvalve to the oil filter was still soft and pliable, and seals well, so it goes back in after cleaning.

[PeWe]

Good photos and description Mark!
They will help at next pump job.

Taking the old seal out was  tricky without damage the alu.
I read about in a post somewhere on this forum  using a thread tap, rather big size to grip it and pull.

[HondaMan]

Good photos and description Mark!
They will help at next pump job.

Taking the old seal out was  tricky without damage the alu.
I read about in a post somewhere on this forum  using a thread tap, rather big size to grip it and pull.

Yeah, I read that, too, but he couldn't remember what size the tap was? Mine don't fit it.

[HondaMan]

Before I forget: I learned that this early Sandcast has a different size (length) of pivot for the can chain tensioner! I never knew this, or at least it wasn't that way on the later Sandcast that I did a couple of years ago, which was much closer serial number to the K0 bikes.

The sandcast's assembled pivot is shorter in overall length, but the (outer) bearing itself is the same as the later engines. The Sandcast's rubber plug-in mounts have longer inner portions that slide into the pivot bearing than the later ones, and the outer (round) portions are shorter. Their overall length, however, is the same. The slot in the top of the engine cases only fits the early, shorter pivot.

So, in this one I got lucky: the inner shaft of the pivot assembly was OK, while the outer was badly pitted and rusted, but it is the same size as in the later engines. Here's some pix showing how wide the standard assembly parts are compared to the engine's hole, and some measurements of the various pieces in case you get caught up in one of these. This pivot MUST be free to flop in your way while assembling things: once in a while the parts come with burrs on the steel collars, and this will seize it up after a short while in use. This leads to the failure of the lower roller as it seizes onto the pivot and gets abused during every throttle-down event.

[BenelliSEI]

The pivot in #581 was the same and I used the same mix of old and new parts!

[MauiK3]

I some times wonder what version of these motors Dick Mann was riding at the Daytona 200 he won.

[HondaMan]

The pivot in #581 was the same and I used the same mix of old and new parts!

Thanks for the note!
I wonder when this changed? The last sandcast I did was toward the end of their run, and it was 'normal'.

[HondaMan]

I some times wonder what version of these motors Dick Mann was riding at the Daytona 200 he won.

Our Honda rep at the time said it was a K0 engine, but with the Yoshimura parts that became the "racing kit" and the lesser cam as Dick's choice, called the "85 HP cam". This would have been 2nd oversize pistons (749.8cc) and a heavy-duty cam chain with harder-rubber guides and steel tensioner roller, maybe a steel guide roller at the bottom side (both came in those kits at different times), a modified sprocket oiler that flung less goo, and the larger carbs we see as "CR" carbs today. The rockers were harder, and the oiler jets at the top were the domed type as found in the K0-K1 engines. I'd wager they had a larger oil hole at the top, too! My guess would be 0.063" size, or so. The fatalities in those engines were all the same: the cam chain tensioner rollers got all chewed up and ate the cam chain. That's what killed all his teammate's bikes: he chose the lesser cam and (n?) less teeth on the rear drive sprocket, knowing the race would bear directly on the bike's weakest link: insufficient top-end oiling over 10K RPM. Today we have 'fixes' for most of these things.

[HondaMan]

Rocker Shaft sleight-of-hand..
The rocker shafts had "good" sides if swapped backward over the cylinders 1-2 side. The shafts are Honda parts: they came as notched-out ones like these in 1969-1970, and simultaneously around early 1970 they became the wasp-waisted type more often seen in the K1 engines.. In the late K2 they became the bolted-down types more often seen after 1996, with the wasp-waisted middles and 2 thru-bolt threaded holes. The late shafts will work in the early engines and vice-versa if the little 5mm lockdown bolts are left out.

[HondaMan]

Sadly, the cam was a different story.
The lobes all had water damage in at least 1 place each, with one lobe fully compromised and the cam sprocket's teeth (below the water level) deeply pitted and misshapen. Even the flat washer that locates the cam is deeply pitted on both sides, so over time it would gnaw away the #1 cam bearing side face, making a lot of aluminum glitters in the oil.

I dug out a very young K4 cam and sprocket I have from a stock-class racing engine that didn't survive the drive chain parting a link one day. I haven't seen a good K0/K1 cam in many years: it would be nicer to have that in this engine, but I don't have one, nor have a source. Most of the K0/K1 cams that sat for a long time in wet-oil engines ("ran when parked") end up pitted in the lobes and inner 2 bearing journals just because of the lesser metallurgy before the 3/1972 build engines. Things got better after that.

With the new cam, all went back together: as soon as I find a cam chain tensioner (this one's missing) I'll be trying to apply oil pressure!