Topic: Just another 71 CB750 K1 (After over a year, I finally got some 4 into 4 pipes!)

[Stev-o]

Sorry to see this Ed, Larry is absolutely right, cases are matched. 

Spare motors are fairly easy to find, maybe buy a parts bike?

[mwvachon]

Ed,
I definitely feel your pain. I was quoted about $300 to repair one of the 'punched-out' K1 case sets I had. It hasn't been a great experience dealing with this - but on the other hand, I now have some valuable experience in tearing down and rebuilding lower-end units on these. I'm almost at the point where I feel like I can tackle anything on these CB750s. The down-side is that these cases don't grow on trees, and you do have to be very careful in selecting anything to start with that is salvage. If it's not a cracked/broken case, it's a stripped fitting, or a broken fin(s). If this was easy, everyone would be doing it!

[edhaeuser]

Ed,
I definitely feel your pain. I was quoted about $300 to repair one of the 'punched-out' K1 case sets I had. It hasn't been a great experience dealing with this - but on the other hand, I now have some valuable experience in tearing down and rebuilding lower-end units on these. I'm almost at the point where I feel like I can tackle anything on these CB750s. The down-side is that these cases don't grow on trees, and you do have to be very careful in selecting anything to start with that is salvage. If it's not a cracked/broken case, it's a stripped fitting, or a broken fin(s). If this was easy, everyone would be doing it!

Yes, I recall that you went through several sets of cases before you found something usable.  I think I will probably try to get mine repaired.  I know a couple of guys around here that do this type of work.

Ed

[edhaeuser]

I have a feeling that my nice new Hondaman book is going to get really greasy in the next few months. :-)

[mwvachon]

Yes, I recall that you went through several sets of cases before you found something usable. 

Yeah, you may not want to look at my latest proj post from today... I think I may need an intervention! ;-)

[01Thomas]

Women like shoes and they can also only wear one pair at a time!

My wife says I have too many bikes in the garage....

[01Thomas]

modified: "K1 Owners unite!"

K1 builders unite !!!................Gary

[edhaeuser]

Damn the torpedos....Full speed ahead.  I'm not going to let a little thing like busted cases deter me.  Just another bump in the road.

It is a good thing that I decided to tear into the engine rather than run it with the fiberglass patch.  I will show you why later.  As expected, My pristine Hondaman book now has greasy prints all over it.  I have to say, for the tear down, the Hondaman book is the bomb.....so much simpler than the manual.  He can get the point across to boneheads like me. :-)

Over the weekend I disasembled the top end and split the cases to see what I was dealing with.  Since I know you guys like pictures, I will post a few random disassembly photos.

DISCLAIMER:  I am a complete amatuer, so if you see any improper techniques, please point them out :-)

Valve cover removed.  Don't forget those two screws under the timing chain tower cover.  I backed off all the tappet adjuster screws for easy removal of the rocker pivot shafts.  I also rotated the engine to relieve all pressure from the rocker arms for each individual tower that I was working on.  Here, I am removing the retaining bolt for the pivot shaft.



Very lightly tapping out the shaft with an aluminum drift (an old exacto knife handle :-) )



one more set of rocker arms to go



After removing all of the rockers, cam bearing caps, and the camshaft, the rocker towers just lift off the engine.  Of course, I labeled everithing as it came off so that it all goes back together the same way.



Head and cyclinders removed.  The pistons and bore look really good.  I don't have a bore guage so I will need to have them measured.  I have a feeling a light hone might still keep me within acceptable limits for a stock bore.  I cannot believe how little wear there is on the bore.





Disassembling the shifter mechanism to get at the bearing retainer so I can split the cases.





I had one stubborn bolt on the front of the case.  I tried heat.  I still snapped it off....grrrrrr.  I will have to try an easy out later on.



Everything bagged and tagged for assembly later on.  Here are just a few pieces.



That's it for this post.  Next up is the cases and the nasty damaged stuff.

[edhaeuser]

On to the cases.  I removed (I thought) all of the case bolts on the top and bottom.  It turns out that I missed a couple, but I realized my error.  No harm done, just a little head scratching.  After all the bolts were out, all it took was a few firm taps with a wood block and hammer to pop the halves loose.  Once it was loose I just lifted the top case off.

Oh yeah, Before I split the cases, I removed the oil pan and found this little present.  All the big pieces from the case damage ended up here.  I put many miles on this bike totally oblivious to what was hiding inside.  Yes, all those chunks you see are metal.




Primary chains color coded with zip ties to mark left and right as well as rotation direction.



Damage to the top case.  before I split the cases, I could not see this damage.



And, the damage to the bottom cases.  You can see that the metal was pushed back and ground away in some areas by the transmission gears.  The arrows show the cracks.







THIS IS NOT MY PHOTO.  A friend of mine had very similar damage to his 750.  He has a welder friend that welded his cases up for really really cheap...like materials and a case of beer for labor :-)  I am going to talk to him and see what he says.  Here is an after picture of his repair.



Ed

[Garystratos201]

That looks like a nice job of welding on the cases and the price is right. Especially if you get to help consume some while he welds. I had the same thing happen to My K1 back in the day and welded the same way and leaked very slightly. Be sure to seal with a good quality sealer when reassembling and you should be ok.......Gary

[Garystratos201]

Nice looking Triumph IW. I owned a 1967 Triumph Bonneville back in the early 70`s at least I believe it was a 1967. Loved that bike...........Gary

[iron_worker]

Can I ask why you are so concerned with how the primary chains are oriented?

IW

[edhaeuser]

Can I ask why you are so concerned with how the primary chains are oriented?

IW

I read that I should do this in the Hondaman book.


EDIT

OK, now that I am back home and not typing on my phone, I will elaborate on my response IW.

A quote from Mark Parish in the "My CB750 Book"

"First things to do here: mark the primary chains as "inner" and "outer", and the direction they are running. The MUST go back in the same positions and directions upon rebuild."

Ed

[Stev-o]

Nice write up Ed.

[mwvachon]

Thanks for the updates/photos, Ed... For me, it's all deja vu - all over again x 2! It's amazing that these things ran with that much metal just sloshing around in the lower case, eh? Make sure to check the play in the primary chains, on two of the cases I opened, they were at the limit or beyond. While you have this opened is the time to address anything that is even questionable! I also inspected all my shaft bearings. The one that goes into the center of the case (part #22 on the parts listing titled as Transmission) was particularly bad in one engine. I couldn't help but think if the gears took a thrashing from the broken chain, SOMETHING must've been damaged in there!

[iron_worker]

Can I ask why you are so concerned with how the primary chains are oriented?

IW

I read that I should do this in the Hondaman book.


EDIT

OK, now that I am back home and not typing on my phone, I will elaborate on my response IW.

A quote from Mark Parish in the "My CB750 Book"

"First things to do here: mark the primary chains as "inner" and "outer", and the direction they are running. The MUST go back in the same positions and directions upon rebuild."

Ed

I just wonder what the reasoning behind it is?

IW

[edhaeuser]

Can I ask why you are so concerned with how the primary chains are oriented?

IW

I read that I should do this in the Hondaman book.


EDIT

OK, now that I am back home and not typing on my phone, I will elaborate on my response IW.

A quote from Mark Parish in the "My CB750 Book"

"First things to do here: mark the primary chains as "inner" and "outer", and the direction they are running. The MUST go back in the same positions and directions upon rebuild."

Ed

I just wonder what the reasoning behind it is?

IW

I'm no expert, but maybe the chains wear into the individual sprockets with use and kind of "mate" together for a lack of a better term.

Ed

[edhaeuser]

Thanks for the updates/photos, Ed... For me, it's all deja vu - all over again x 2! It's amazing that these things ran with that much metal just sloshing around in the lower case, eh? Make sure to check the play in the primary chains, on two of the cases I opened, they were at the limit or beyond. While you have this opened is the time to address anything that is even questionable! I also inspected all my shaft bearings. The one that goes into the center of the case (part #22 on the parts listing titled as Transmission) was particularly bad in one engine. I couldn't help but think if the gears took a thrashing from the broken chain, SOMETHING must've been damaged in there!

I will definately check the bearings out.  You are right.  As long as I have it apart, I should make sure everything is in good shape.

Ed

[edhaeuser]

Can someone please tell me how this kickstart shaft retaining pin comes out? (The hollow one) I can't see anything holding it, but I can't get it to move.


thanks

[MoMo]

It is a roll pin, you'll need to heat the aluminum case, pinch the pin and pull up.  It can be a tough one  to remove...Larry

[edhaeuser]

It is a roll pin, you'll need to heat the aluminum case, pinch the pin and pull up.  It can be a tough one  to remove...Larry

Got it. Thanks!!  I used heat like you said, and ended up running a small tap in the end of it so I could thread a small bolt into it.  Grabbed the bolt with a vice grips and whacked the vice grips with a hammer to break it loose.

[MoMo]

It is a roll pin, you'll need to heat the aluminum case, pinch the pin and pull up.  It can be a tough one  to remove...Larry

Got it. Thanks!!  I used heat like you said, and ended up running a small tap in the end of it so I could thread a small bolt into it.  Grabbed the bolt with a vice grips and whacked the vice grips with a hammer to break it loose.

Good idea with the tap...Larry

[mwvachon]

I've actually just been taking a pair of needle-nose vice-grips and getting a good bite on the pin and was able to work the few that I've done straight out. The fun is getting it back together...

[cheftuskey121]

keep at it Ed, I am watching this engine rebuild with a strong eye. please take LOTS of detailed pictures and explanations. I'm sure I will be needing it some day!

[edhaeuser]

keep at it Ed, I am watching this engine rebuild with a strong eye. please take LOTS of detailed pictures and explanations. I'm sure I will be needing it some day!

I will try to keep up the pictures.....  There are so many good engine builds on here already, I feel like I am rehashing material that has been covered so well in the past.

I've actually just been taking a pair of needle-nose vice-grips and getting a good bite on the pin and was able to work the few that I've done straight out. The fun is getting it back together...

I tried the needle-nose first and then a vice grips on the pin.  I could not get it to budge, everything just slipped off.  Even with heat and a bolt threeded in, it took considerable force to get it moving.  Yes....getting it back together...that will be a challenge.

Ed