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Engine rebuild - to bother/not bother


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My early K750 resto.

I have the frame in bits, along with the wheels and other stuff.

The rear mudguard is worse than I thought and I keep looking it ....

 

The engine itself, on the other hand, seems pretty good and unworn

The speedo reads 9k km.

The pistons are standard, the ring gap is well within spec and there is no wear in the barrels at all. I will get new rings and relap the valves as a matter of course.

The big ends feel great, the little ends have no play, the clutch is good, as are the clutch pins, and also cam and crank gears.

The bottom of the sump does have some deposits, but they all get that.

 

I am wondering if it is really worth stripping it down to take a look at the oil slinger, which is likely pretty empty too.

It's a dilemma as if I strip it that far, then I must replace the bearings with modern SKF stuff. I think I will also need:

  • rear and front crank bearing
  • cam bearing
  • Some seals ? I think there is one in the back and one in the front ?
  • I believe I will also need a big socket for the flywheel bolt and a puller ( tools for one use .. grrrr)

 

I bought this bike really, really cheap and wanted to get it done on a budget. However the wheels, especially, are really going to knock the cost up .

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Is the oil slinger that your mentioning. The centrifuge separator? And is it not external of the crank like a 650 Dnepr? And if so . Why replace the bearings? Or is that being a little obsessive? Just asking because I have to catch myself sometimes. Always trying to somehow make it BETTER (= stupid money) on something Ill never relize that money back if sold.

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I went through my M66 gearbox. I replaced the bearings - it was quite easy. Some of the bearings were a bit gritty when I took them out - stands to reason as the M66 was a cheap as chips motorcycle and therefore owned by people who thought maintenance was too expensive an endeavour to worry about. My slinger was also full of crap.

I'd do it. Puller and other tools can be made or borrowed - and if you buy it'll make maintenance of your fleet a bit easier. Whole enterprise shouldn't take more than a weekend once you have all your bits to hand and you can then dispense with worries.

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The oil slinger is internal - the crank needs to come out and this is my primary reason for considering a complete engine strip.

 

So, should my shopping list consist of:

  1. 36mm socket for the flywheel bolt ( I think I have a 36mm one !!)
  2. harmonic puller for the flywheel
  3. bolts to mount the puller (thread size anyone ?)
  4. front crank bearing 72x35x17
  5. rear crank bearing 72x35x17
  6. cam bearing (front)52x25x15
  7. cam bush (rear)
  8. new felt seal for rear bearing
  9. new seal for the front crank 16x30x7
  10. Is there a seal on front of the camshaft ?

Do I need new bolts for the bearing carrier or flywheel or anything ? How about tab washers ?

 

Don't worry, I have enough british bikes to deal with the valves. I guess I should have said clean up/lapping depending - they need to come out to check the guides.

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I'd just ride it, and then fix it if it breaks..

My KMZ K750 did something like 10000 km with an engine using random used pistons in the cylinders that had been running for a

while with broken rings, and a lot of play in the crank.. it was noisy yes, but it ran..

 

After a while it had a catastrophic failure, but I'm pretty sure that was due to me being stupid and not noticing it not running on the right cylinder...

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The flywheel puller bolts should be M10x1.5 about 75 mm or longer. The bearing carrier puller bolts should be M8x1.25 about 75 mm or longer. (I say should be as there's a chance earlier bikes used metric fine, but I doubt that for puller bolts).

 

Crankshaft bearings are 207 with a C3 tolerance - sloppy.

Camshaft bearing is 205

You could probably replace the rear felt seal with the later seal. Contact Serious Black about that, he's the SV expert.

I always replace the flywheel bolt and tab washer as they're cheap from Sidecar Pro. Almost everybody re-use them. You'll probably need a rattle gun to remove it.

The bearing carrier bolts are lockwired. I reuse them but use Loctite and rewire them.

 

post-1839-0-36006300-1501747245_thumb.jpg

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Im of the fix it before it breaks variety. It's not a big job and peace of mind is worth something. For a couple of hundred bucks you get an engine that has the basics covered. Depends on whether you intend to keep the bike for years or if it's a short term novelty.

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My $0.02

Depends on your Skill set, and experience level with Old MC engines..

Experience is capable of determining what is good/bad about any piece of equipment..

I have Never experienced any engine Failure, that did Not Announce itself prior to Exhibiting itself.

Anything that is going to fail without any warning is Usually Not something that is Easily detectable.. IMO

Therefor, Even [actually especially] newly rebuilt engines have certainly been known to fail...

In fact, I have friends who shouldn't Own Tools!!! Because I have seen many more problems caused, than they have Cured!!!

YMMV

and Not knowing your Skill set, it is Not Possible to make a Recommendation!!!

FWIW

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