Topic: Thinking I am going to do a complete engine build 78 cb750k

[RAFster122s]

Bottom line is it may be quicker than stock but a more modern motorcycle can leave you in the dust. So trying to get major horsepower really isn't worth it or then you have to start chasing way better braking and similar things. Better to put your money in suspension improvements and modest build.  Chassis flex will limit the capabilities, but many never see that or feel that when riding. Plus, you never should be pushing a street bike that hard on public roads. Braking distances adding one second of delay to reaction times before threshold braking gets to be scary number in real life at low speeds, much less high speeds.
Seen it demonstrated to me in riders instructor at 15 and 25 mph and adding a single second really changes stopping distances by huge factors. Logarithmic distance increases as speed increases.

You will be happy with a strong engine and good perfance if your suspension and brake system are equally in good shape.

That's my unsolicited advice.
Dav9d

[Dime]

Bottom line is it may be quicker than stock but a more modern motorcycle can leave you in the dust. So trying to get major horsepower really isn't worth it or then you have to start chasing way better braking and similar things. Better to put your money in suspension improvements and modest build.  Chassis flex will limit the capabilities, but many never see that or feel that when riding. Plus, you never should be pushing a street bike that hard on public roads. Braking distances adding one second of delay to reaction times before threshold braking gets to be scary number in real life at low speeds, much less high speeds.
Seen it demonstrated to me in riders instructor at 15 and 25 mph and adding a single second really changes stopping distances by huge factors. Logarithmic distance increases as speed increases.

You will be happy with a strong engine and good perfance if your suspension and brake system are equally in good shape.

That's my unsolicited advice.
Dav9d

Both the brakes and the suspension are being upgraded. The bike will have dual disc front, single disc rear. The suspension will be progressive rear and single rate front springs. Haven't decided about eliminators in the front yet. This is going to be using the kz1000 ltd forks and eliminating the air portion.

This bike will be a cruiser. Not going to be pushing anything. Just want it to be responsive on the engine as well as the handling

[Don R]

  None of this is really sensible dollar or performance wise. I hear the same thing on the Suzuki GS page, don't bother, new bikes are faster.
  That doesn't mean I don't love riding and working on my old Honda barn rat drag bike or the 81 GS1100E I snagged last year and it surely doesn't mean I'm not close to putting my cb750 based 1124 stroker motor back together. Who knows, maybe even the old ATP turbo kit. 

[Dime]

  None of this is really sensible dollar or performance wise. I hear the same thing on the Suzuki GS page, don't bother, new bikes are faster.
  That doesn't mean I don't love riding and working on my old Honda barn rat drag bike or the 81 GS1100E I snagged last year and it surely doesn't mean I'm not close to putting my cb750 based 1124 stroker motor back together. Who knows, maybe even the old ATP turbo kit.

I agree. I have a tattoo around my wrist that says "better rodded than rotton".  If I wanted out of the box performance a modern bike would be better. I just want to have some fun on my dream bike. Nothing crazy just dependable, twist the wick, enjoy the ride type fun. Always wanted a sohc Honda. Now I get to build one from the frame up and get exactly what I want.

[RAFster122s]

I find it more fun to ride a slower bike and be able to take corners and enjoy the scenery in an upright position in a comfortable position without my wrists bothering me or my low back or neck complaining about being crouched over. That's why my storage building and modern bike all feature upright riding positions and the adventure bike which is the modern one gives me that same sit up and beg easy on back and neck riding comfort.

[Dime]

If I was questioning doing a full rebuild all doubts are now over.

Besides finding all this in the oil pan the primary measurement is 67.3mm. Still serviceable but not ideal.

[Dime]

The screen seems to be doing it's job but who knows what actually passed through this engine

[seanbarney41]

Meh.  Once again, that's basically what's you find in every mildly abused or poorly cared for cb engine.  I have found that so many times, clean it out, fit a new gasket and enjoyed the next 20k miles.

[Dime]

Meh.  Once again, that's basically what's you find in every mildly abused or poorly cared for cb engine.  I have found that so many times, clean it out, fit a new gasket and enjoyed the next 20k miles.

Figure the primary measument at 67.3mm is still good for awhile yet too? The tensioner is in good shape. On the hard side but good.

[seanbarney41]

Meh.  Once again, that's basically what's you find in every mildly abused or poorly cared for cb engine.  I have found that so many times, clean it out, fit a new gasket and enjoyed the next 20k miles.

Figure the primary measument at 67.3mm is still good for awhile yet too? The tensioner is in good shape. On the hard side but good.

I don't know any numbers and have never worried about the primary chains on anything but the hairiest scariest engine combo's...never seen or heard of one failing.

The one thing that needs to be checked on a bike that has not been ridden is the transmission, in my opinion...one of the few things that goes wrong on these

[Stev-o]

Besides finding all this in the oil pan...

What are those "sesame seeds" in there? Doesnt look like metal.

[Dime]

Besides finding all this in the oil pan...

What are those "sesame seeds" in there? Doesnt look like metal.

That was air bubbles in the oil.

I just cleaned out the pan onto a clean piece of cardboard and there are a couple of very small flakes of metal but nothing indicating a failure

[BenelliSEI]

Get it running. Usually a complete tune up, clean carbs, fresh plugs and caps, points etc and you’ll be amazed how well it runs. Put a few hundred miles on it before tearing into it!

[Dime]

Get it running. Usually a complete tune up, clean carbs, fresh plugs and caps, points etc and you’ll be amazed how well it runs. Put a few hundred miles on it before tearing into it!

Way past that now, LOL. The bike is down to the frame, the engine is out due to low compression, the top end is off and is micing out of spec.

Definitely into a bore job but if you guys are not too concerned about the debris and the primary chains measuring at 67.3mm than I will just pull and clean the oil pump and reseal it. Got to re find the thread I saw about that.

[Dime]

Meh.  Once again, that's basically what's you find in every mildly abused or poorly cared for cb engine.  I have found that so many times, clean it out, fit a new gasket and enjoyed the next 20k miles.

Figure the primary measument at 67.3mm is still good for awhile yet too? The tensioner is in good shape. On the hard side but good.

I don't know any numbers and have never worried about the primary chains on anything but the hairiest scariest engine combo's...never seen or heard of one failing.

The one thing that needs to be checked on a bike that has not been ridden is the transmission, in my opinion...one of the few things that goes wrong on these

I forgot to mention my buddy I bought this off had been running it up and down the road going though the gears before he parked it. So the transmission should be good to go

[Stev-o]

Meh.  Once again, that's basically what's you find in every mildly abused or poorly cared for cb engine.  I have found that so many times, clean it out, fit a new gasket and enjoyed the next 20k miles.

Figure the primary measument at 67.3mm is still good for awhile yet too? The tensioner is in good shape. On the hard side but good.

I don't know any numbers and have never worried about the primary chains on anything but the hairiest scariest engine combo's...never seen or heard of one failing.

The one thing that needs to be checked on a bike that has not been ridden is the transmission, in my opinion...one of the few things that goes wrong on these

I forgot to mention my buddy I bought this off had been running it up and down the road going though the gears before he parked it. So the transmission should be good to go

Then why are you doing a complete rebuild?!  I dont get it.

[Dime]

Meh.  Once again, that's basically what's you find in every mildly abused or poorly cared for cb engine.  I have found that so many times, clean it out, fit a new gasket and enjoyed the next 20k miles.

Figure the primary measument at 67.3mm is still good for awhile yet too? The tensioner is in good shape. On the hard side but good.

I don't know any numbers and have never worried about the primary chains on anything but the hairiest scariest engine combo's...never seen or heard of one failing.

The one thing that needs to be checked on a bike that has not been ridden is the transmission, in my opinion...one of the few things that goes wrong on these

I forgot to mention my buddy I bought this off had been running it up and down the road going though the gears before he parked it. So the transmission should be good to go

Then why are you doing a complete rebuild?!  I dont get it.

The thought about going into the bottom end was insurance.

Between the poor maintenance I am finding on this bike and what I am reading about the primary chains I thought it might be a good idea to address it all now if need be.

If the debris I am finding is of no concern, it almost looks like gasket material, and the lack of metal shavings, if the primary chain numbers are not alarming, then there is no reason to do the bottom end.

The top end definitely needs to be done but I knew that anyway.

I am new to these engines so I trust your guys judgement.

[M 750K6]

I had top end problems requiring engine out. My primary chain was at 68.2mm, so I was tempted to go in. However it quickly gets expensive. I resisted and sorted the head out, to then ride the bike and see if I like it.

Several thousand miles on. Bike's pretty much perfect.

[Dime]

I had top end problems requiring engine out. My primary chain was at 68.2mm, so I was tempted to go in. However it quickly gets expensive. I resisted and sorted the head out, to then ride the bike and see if I like it.

Several thousand miles on. Bike's pretty much perfect.

Good to hear. Thank you

[M 750K6]

Bet I've jinxed it now! But I do love my 750k6. Gorgeous looking bike.

The advice you've had from folk more experienced in these bikes than me, is pretty refreshing. There's clearly a lot of confidence in these engines.

[Stev-o]

This is a really bad pic but I bought a bike and this is what I found when I removed the oil pan.  The bike ran fine with no issues so I was not concerned, installed a new [polished] pan and the bike has been fine for years.

[Dime]

This is a really bad pic but I bought a bike and this is what I found when I removed the oil pan.  The bike ran fine with no issues so I was not concerned, installed a new [polished] pan and the bike has been fine for years.

Ya man that is pretty nasty. I am looking into rebuilding the oil pump. I want to check that out at bear minimum. Been reading a few posts that PeWe put up on breaking it down and removing the inner shaft seal.

My hope is the pump gears are not torn up. Definitely want to do the pump rebuild at minimum for peace of mind.

[Dime]

Broke down the pump last night the gears have some marks on the top and bottom but nothing I can get a fingernail in. The inner part of the gears where they mesh together are near perfect.

I can't find anything on the oil pump in the manual, I am sure I am just missing it. Will have another look now.

[MauiK3]

Replace the consumables, freshen up the top end, go 1 or 2 over on the cylinders, new pistons and ride into the sunset!

[Dime]

Replace the consumables, freshen up the top end, go 1 or 2 over on the cylinders, new pistons and ride into the sunset!

I dig it man!😎 I am either going with 62mm pistons or a 836cc kit. I have both lined up for a great price.