Topic: Rebuild the K3 Basket case.

[Pecantree]

Decided to rebuild the 750 K3 engine now as I have it in hand. Won't get my K6 back till xmas. (Thanks brother!)
Hopefully just swap out engines so I can get it back on the road!
Recounted here.
Bought this on CL from a kid who's a dirt bike racer.  He'd started a rebuild and then abandoned it.
I think he was rebuilding it in the dirt.
I used to rebuild VW engines 30 years ago but this is my first bike engine.
I have Hondamans book and am following his directions for teardown and rebuild.

A bunch of parts, and a basket! Carbs and  whatnot all thrown together.


And an engine


Here's the carbs sorted out. Internals are marked but I can't find any marks on the bodies or slides. I'll sort these out later but for now just padded them in a box and stashed on the shelf.


Teardown!
Inside of the valve cover. Are the metal edges supposed to be broken like this?


Top of head. Missing the center bolts that go in the center of the rocker towers. Would the shafts have even stayed in place without them?  In reassemble I'll lose the two 5mm bolts on either side of the new center bolt.


In taking the cam shaft off the top and bottom cam bearings were mismatched.
Next was pulling the head. Several of the flanged nuts were missing washers.

Flipped the head over and found some major gouges by the cam chain tunnel.


Also there is a small amount of warpage on one end of the head. Should I have the head reurfaced?


Pulled the jugs off. Whats up with the o-ring around the cylinders? It looks like it was put in during an earthquake. up and down. All 4 of them are like this. Do I need to replace these?


Pulled the pistons. Here's a picture. I think he used a belt sander!

A closeup of one

Do I need to buy new ones or can I sand and polish the tops of these?

I'm going to split the case because of the amount of grit! And I want to know what condition it's in.
The Kid put new rings and valve's in. I have to buy a valve compression tool first. Looking into the exhaust ports I can see some rust on the seats. Hopefully I can lap it out.

I know I'll have more questions as I get into this deeper.
Thanks!

[d9canada]

Pecantree,
I haven't done a 750 SOHC but I've done a top end on a 900C DOHC, and several sets of CV carbs for same, so my experience is limited and different.  I won't comment on most of your questions directly other than to say your worst suspicisions are pretty much your best re head level (although the service manual should state the allowable limit from flat), the O rings, etc. 

However on the carbs, the uppers may be stamped with 1,2,3,4 and if not you can figure it out.  From the pictures it looks like one carb has a choke actuating lever so that's #1 (rider's left).  Find another where the choke and fuel tubes go in only on the left and are plugged on the right.  That's #4.  Number 2 has the choke spring etc. on it's right side and Number 3 has none of that stuff. 

Here's a link that hopefully covers your carb version:
http://www.salocal.com/sohc/tech/carb/carb.htm
Click on a picture to expand it and follow the steips.

Hope this helps

[ekpent]

Those missing center bolts that go through the rockers towers have a tendency to strip out very easily,may be why they are missing. Be a good idea to just helicoil them while everything is apart,especially if they feel punky at all 

[Rigid]

Measure everything per the manual, replace all gaskets and seals that come in a Vesrah kit, plus any that are suspect, clean thoroughly, apply engine assembly lube as you go back together with correct torque values, don't trust anyone elses work, rock on.

[Pecantree]

Rigid.
Your location sig sounds like directions for getting that itchy spot on your back scratched!

[AbbyRider]

Your valve cover photo showing the missing chunks is similar to the photo and questions that I just posted today (see post "Three Top-End Questions). I think the walls there are fairly thin, and maybe the cam chain flies around a bit and knocks the metal out?

[ekpent]

Rigid.
Your location sig sounds like directions for getting that itchy spot on your back scratched!

  Sounds like it may be in Indiana,down a little and closer to the left side.   

[Pecantree]

Down sick the last few days. Ordered some parts for the 360 and the clutch nut tool.
When that comes I'll pull the clutch basket and get into the bottom end.

Able to spend some time with the top end parts today, along with various gauges.
Realized that the Kid was just slamming some new parts in here and was gonna run it like that.
He'd cleaned it, put new rings and valves in but nothing else.

Measured the cylinder bore's.  #4 is the worst at 61.38mm, the others are a little less but still outside limits.
This answered my questions about buying new pistons as they are standard.

I do have a question about the head, the top left rear corner cooling fin is broken.
Can I still run with this? I think it will be alright, just slightly hotter right there.


Also purchased a valve spring compressor and pulled the valves.
Measured the Valve/Guide clearance per the shop manual.
Intakes are way loose, around .008, Exhaust is much tighter but will have all replaced.

This will all go to the machinist when I find one. Any recommendations for Austin, Texas!
Still want to strip the black paint off the head and cylinders. It's chipped and applied much to thick.
Trying to keep a stock look.

Thanks
Steve

[78whiteorbs]

I dont think that fin is gonna slow you down but aesthetically it's an eyesore. What you need is a donor head to harvest some fins from , then tig and file down accordingly- also have heard you can JB them and file but the epoxy isnt gonna transfer the heat. 

Being as you already have the engine out and apart why not just get another head ? There are plenty of them and pretty cheap-  if you do go that route let me know , I could use some fins too !

[CycleRanger]

This will all go to the machinist when I find one. Any recommendations for Austin, Texas!

Thanks
Steve

Give these guys a call: http://www.limeybikes.com/

They can probably put you on to a reputable machinist.

[Xnavylfr]

There is a place  that specializes in CB750s. They also have all the kits to go as big as you DARE on the bore.
http://cyclexchange.net/ call them and talk to KEN.
The break out on the HEAD is that way on every bike I've seen apart.
The broken fin does'nt hurt the engine just the looks, I've NEVER heard of cutting fins from a head and adding it another but I have heard of the JB WELD to build up a new fin, this is only good if you repaint it.
 The .002 on the head will be taken up with the gasket and not enough to worry about. IF you do have it milled flat you will need to clay the top of the pistons to make SURE you still have clearance in the valve cutouts ( TAKES A LOT OF TME)to do!!
If you clean the inside of the valve valleys (ESPECIALLY the intakes) don't make them SMOOTH, this will not atomize the fuel/air mix properly.
If you need MORE info check HONDACHOPPER.com  Lot of great people there and YEARS of experience on these beast!

Xnavylfr(CHUCK)

[Pecantree]

Finally had some more shop time and have broken the case down.
Lot's of questions as I've never been into one of these engines before.


Pulled out the primary chain tensioner and noticed what looks like abrasion. The edge is very sharp.
Is this an oil capture feature?


Down to the counter shaft. Lots of wear on C5.


Guess I'll be on the lookout for a low mileage gearbox.


Didn't picture it but all gears that slide on bushings have very perceptible wiggle motion.
The gears themselves seem to be okay.
Hondaman's book talk's about boreing out the center of the gear and having standard bushings installed.
Does anyone have experience with this.

Here's a shot of the shift forks. The tangs themselves are within tolerances. The inside seems to have a lot of galling.
Is this passable?


The kickstart gear has a good amount of wobble. Mark's book talks about a loss of oil pressure because of this. May be looking for a good used one also. The rest of the dogs and gears on the mainshaft seem to be okay except for the bushing wobble. I'll see what turns up with a replacement tranny.
Spinning the shafts while listening to the bearings I can hear some gritchies. This engine has unknown mileage on it so I'm going to replace the bearings.
Here's what the bottom looked like after everything was out. Lots of ceder needles.


Thanks All!
Steve

[Pecantree]

Recap my questions from the last post.
Does the primary chain tensioner have a oil capture feature or is this abrasion?
Is the wear on the shift forks okay?
Has anybody done oversized bushings in the gears?
Pictures in my previous post!
Thanks

Removed the cylinder studs last nite and ended up breaking the #4 cyl rear outside one.
Even after a week of soaking and a torch.
I'll leave this for the machine shop. It's snapped flush with the case.
Oh well!

[Old Scrambler]

What is the goal.............standard rebuild or high-performance?  I would get a replacement barrel with good fins........any K2 - K6.  Same with tranny.  Cycle X has the best gasket kits because they are new and have all pieces required for every model. The cam-chain tensioner looks OK if the wheel is free.

Keep the head for asthetics..........its an early casting like the K2 but with later internals.  Think about the Honda-Man advice regarding the low-cost 836 piston kits on ebay.........he likes them if they are prepped and installed correctly.