Topic: CB750 K2 engine + bike project, frame will come

[PeWe]

Cleaned the bench enough to work on a refurbished ported old head. This before doing the engine that will invade the bench for a longer time.
Small jobs first

I found the head at a bike scrap yard for 6 years ago. Home ported early head, probably K2.
I let my shop nearby restore and improve it earlier this year.
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UPDATE:
This head work fine on my billet block 1005cc. The top case on the K2 engine this build will use is bored to welcome the billet block.
Intitially an 890 kit to be used.

For this K2  bike build, the billet block's first head that had 5mm  34/28mm valve  kit where guides were totally shot after 21.000 km. That head restored with CycleX iron guides 6.6mm stems 34/28 mm valves
*****************

Valve guides were OK. Inlets ported further to use my F2 34mm inlet valves earlier used in my K6 head that got 5mm stem kit.
(Have CycleX shiny 34mm K valves and TI retainers for all to be done before next use. That inlet valve fill the chamber more than stock F2 in valve. Tested and measured chamber to be 0.3-0.4cc less)

Ex valves Kibblewhite also from my K6. Only around 5000km.
Port job to make it look good and mounted my old not used valves and my Action Fours springs from the 80's with controlled spring force.

Head have some bad threads I have to fix. Shop need to be paid per hour for a job I can do.

I do not like helicoil. Risk that they either come up with bolt or will damage bolt thread since the small end is not removed enough at assembly.

I prefer Time-Serts.

The head had one really bad repair, M8 cut bolt drilled and threaded for M5! When I got it off suffering an x- screw bit I hammered into it and could grip the bit and unscrew it.
When off I found more, M8 helicoil!
Off it went with help of a small screwdriver and hammer.

I'll enter a Wurth self threading insert OD 10mm, M6 inside, drill 8.7-9.4mm before in that big hole.

The other cam holder bolt pair bolts will get the size smaller of Wurth self threading inserts, OD 9mm. Drill 8.2-8.6 mm before.

One hole is drilled thru so it must get a new bottom with help of JB Weld before thread insert.

When the threads are fixed on this head, another head need to be fixed. An old K1 head with smoky ex guides without seals My K2 used earlier this year..

 I'll remove valves and check them all if OK before the shop will replace ex guides. I have in guides too.

[PeWe]

Here a K1 engine not to be used in this build.
An old bottom end. Rod 2 is stucked on crank.
I have " warranty" getting usable parts if not possible to use

I hope I'll can use stock cyl studs. I think these are PITA to remove.

Case is welded near rear right hanger bolt. I'll see how it look like when apart. As it look now I can grind and apply some JB Weld to almost stock look.

I can visit my friend that sold it to me. He has several complete  cases, K1, K2, K6....

[PeWe]

Some threads fixed.
1 self threading insert OD 10mm
Prepared for the 9mm version. Glued bottom with JB Weld. From under thru the rubber puck hole JB Weld Putty that blocked hole. Then JB Weld from inside. Dropped acetone on top to let it flow better.
 Insert will enter tomorrow when hardened enough.
2 other threads fixed with Big- Sert inserts.
The other holes with knock pins have helicoil that might be OK.

 PITA to remove that deep under the knock pin area. One seems to have helicoil way to deep. I intend to use Honda bolts so threads must sit where it should, not too deep.

All inserts fastened with red Loctite 272 except for the biggest one  and time-sert at cyl 1, thread with knock pin that got green 648.

Studs look OK. Their holes to be sealed off in the plug cavity with JB Weld to ensure no future leak that way.

[PeWe]

Bolt test on head successful!
All threads found by ease, one deeper time- sert landed nice. Knock pin have room and bolt thread lenght like the other. Threads not tested by torque. Later try with 10Nm.

I had to search for my new bolts from France. Not sold everywhere and rather expensive.

One thread not inserted yet, have to wait for JB Weld to harden to a sealed bottom not leaking oil. 

[NalydStrea]

That looks good, I hope the J-B Weld holds up!
I'm using helicoils in mine, because that's all I have laying around.
You're not a fan of them, but what loctite would you use on them te prevent them from coming back up?

[PeWe]

I use Loctite 272 most of the time on the time- serts.
Some of them got the harder Loctite 648 designed for gluing bushings, bearings and similar.

JB Weld work fine, here only plugging the hole drilled too deep by PO inserting helicoils. I did not replace all helicoils, only those that looked crappy, with bad threads abusing the bolt.

I'll perform a thread test tighten all cam holder bolts and nuts by 10Nm, valvecover will get same torque.
All threads look OK.

[Stev-o]

Hey PeWe....subscribed

[PeWe]

Hi Seve-o,
welcome to this thread

I took home bore micrometer and std micrometer from my jobs lab to measure my recently bored cylinders with their pistons to verify clearances.
+ 0.5mm cylinder K7/K8 pistons my K2 will get.
Cylinder with used 836 pistons
Total clearance around 0.025-0.03mm

Cylinder with 849 pistons a little bit loser fit 0.04-0.05mm.

900cc cylinder, lightly used with forged pistons 0.06-0.08mm. Another quick treatment with flexhone 10- 15 quick strokes did not make much, max 1/3 of an hundreds mm.

Lets see which cylinder this K1 engine will get. Risk for more hp in need of better rods.

I need another registered frame

[PeWe]

4 threads did not survive the 10Nm torque test. Typical for these, look good  but start to spin when bottom the cover .
Threads gave up early.

I'll see how many left that have  no insert or working helicoil. Maybe better to do them all. I guess 2, 3 more than these bad 4.

Update: I found 5 threads without good helicoil or inserts. I'll do them too. A few of them WILL cause problems at a future cover off or retighten  or just crack and cause a leak.
9 inserts more to do.

I need to order more Time- serts. Engine covers on that K1 engine will most likely need 10 more. My 2 bikes will need at a future cover work

[Terry in Australia]

Subscribed Per, and timely for me too, I'm pretty sure my early K1 head will need some threads repaired too, when I start the build. Good job!

[PeWe]

I had a weak moment today when I concidered cheaping out using cheap helicoil type of thread repair.
I noticed that one of the bad threads that gave up when test assemble the cover was a helicoil. Bad mounted one. I had to use a Big- sert in that hole.

I have ordered 25pcs 9.4mm M6 Time- Sert from UK.

I have also an eventual self threading inserts order  from Hongkong if OD is 9.0mm.
I have same size from Wurth. 9.0mm OD, M6 ×12mm
Good for threads with meat around. Wurth cost a lot, China a little.
This head got 3 of that model holding the cam holders. One neded one size above, OD 10mm.
Pic from today.
There is a risk that the K1 engine will get this head, ported with  F2 34mm inlet valves using lash caps.
900cc cylinder would be a good match. It is an early model with CycleX "915 kit"

 I need to look for better rods.  My CB750 repairing and part hording friend has rods that look like old RC steel rods, OEM with bushing in the small end. Maybe MTC or AF?

[RAZZ]

Hi Per

It looks really good, i have a old head with old beat up helicois in both camtower and cover holes.. ( the old hot head from spinning wheel ) Can you put some links up from where and what to buy ? I live relativly close to you, north of Copenhagen so i Think i Can get same shipping as you - Thanks in advance


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[PeWe]

I ordered Time- Sert kits from threaddoctor US on eBay.
Inserts, drill, tap etc.
I have found on eBay UK too.
It cost more today to order from US.
 The threaddoctor can be better to order from their home page and hopefully avoid multiple shipping as eBay wanted last time so I was forced to delete my orders.
 Not multiple small itens in one shipping

Denmark might have better customs as Sweden where we now have to pay customs fees for orders under 50 USD, a few years ago direct to mailbox when max 50 USD.

They have Big- Sert kits too. Also good to have when fixing ruined helicoils .

Order extra inserts. M6× 9.4mm lenght very useful. Some 12mm lenght good too, when upper oart oif thread is bad but can get good thread fit deeper.

I fasten the inserts with Loctite 272 red hard hi- temp. Some with looser fit, replacing helicoils with time- serts  Loctite 648 green made for gluing bushings.
Loctite found on ebay UK for good price. It cost 3 times more here.

[BPellerine]

I fixed some on my ko head,then others would give out,finally just did them all,had the cam towers on and off a few times,got tired of that.bill

[PeWe]

I did the rest of the time sert install. As usual not deep enough seat cut for insert upper wider part on most of them so I had to file the insert flash with gasket surface. I used the battery drilling machine which cut easier and deeper, still not enough. 0.5mm more next time to ensure no filing. Mostly 0.1-0.2mm stickout.

I refreshed all threads with M6 tap afterwards for smooth surface and easy for the future M6 bolts.
The few good helicoils got a drop very thin Loctite 290 each that hopefully could creep inside thread and lock them better against head.

[Terry in Australia]

Is there a Loctite product that's impervious to hot oil Per? I've tried several, but found them to be useless once hot oil comes into contact with them?

[PeWe]

Loctite thread lockers should withstand hot oil.
I have used on cam bolts many times (blue 243 or similar). It sit good at next removal.
272 for higher temps and no plans taking it apart again.

I usually clean with acetone first, no oily threads.

222 ( weak) my new favourite for all kind of bolts that can vibrate and come loose. Like front sprocket M6, rear exhaust bolts.

[PeWe]

Another head.
Stock K1 I suppose, with ex guides without seals.
New ex guides and all valves to be installed. I gave it some thread fixes 1 year ago.

[PeWe]

The build will use a K2 1975 case.  The old K1 bottom end will wait.
Transmission and crank from a K7 or parallel F bike from 1977 or later.
The final shaft need to be replaced by a K where the final sprocket with new bearings will be mounted on.

Removed all stock cyl studs with 2 nut and 2 spanners. Worked fine. The trick was to keep the nuts tightened with the 2 spanners with my both hands, a short quick twist tighten the stud made it to click, next remove it, sprayed some WD40 to lube the threads.

One block is glass beaded, probably before welding the font lower hanger bolt ear to easier find eventual other issues.
Both block match when looking inside, Honda graffity and old sealer. This block also a BBBBB block as both my CB750 have.

I added a thin layer of acetone thinned JB Weld in the ign cover lower thread I have repaired, built up the ear with JB Weld. I'll refresh the thread with an M6 tap when fully cured. It was a little loose after molded the thread with a bolt fastened.

I'll do a test build bolting cases together with all covers to verify all threads. Learned from earlier restores that a thread look OK, but spinn when tighten the bolt. Easier to install thread inserts before assembly. No worries to get metal flakes inside.

[HondaMan]

Here the engine. An old bottom end. Rod 2 is stucked on crank.
I have " warranty" getting usable parts if not possible to use

I hope I'll can use stock cyl studs. I think these are PITA to remove.

Case is welded near rear right hanger bolt. I'll see how it look like when apart. As it look now I can grind and apply some JB Weld to almost stock look.

I can visit my friend that sold it to me. He has several complete  cases, K1, K2, K6....

I have seen quite a few of the K1 with the welded top left rear bolt boss. The chain, when it broke, whipped up there and cracked it, just before it took out the sprocket cover like a chainsaw... 

[PeWe]

This K1 case is welded on the other side, not sprocket side.

The K2 case I started with is welded on right lower side.

It is interesting to know how this happened. Maybe a collision or crash with both sets of cases?

About snapping chain, My K6 (blue avatar) snapped its chain (July 1988) on Autobahn in an uphill to pass slow going trucks, geared down twice to 3rd and WOT. It snapped direct. I was lucky to see a side pocket direct where I could park. I was waiting to see dripping oil. No oil, real luck!
Chain almost sliced the registration plate, chain cover sat loose when brackets on swingarm snapped.
A new chain and chain cover with the luggage (later tossed in France) and we could continue.

Chain had too much slack, had plan to fix it at next gas stop. DID 50HDS o-ring chain. Rear wheel got chew marks from the chain, the flat area inside the sprocket. If no chain cover that took part of the hit, probably damaged hanger.

[PeWe]

I had to verify the transmission I'll use. It was purchased as an CB750F-75. Found that the final shaft is a later model as K7, F2 use.
I had to check the gears that differ from earlier K just for sure. The seller might have mixed up parts. The final gear is differrent and must match correct trans.
Trans OK! I compared with an old K6 I have.

The parts must have been taken from an F2. I have complete crank with rods, starter gear and alternator from same engine. It look fine and not much used as the trans and primary hub.

Counter shaft has one gear with 32 teeth, K6 31. (In the end towards the gear mechanism)
Main shaft has one gear closest to primary hub: 30, K6 has 31 teeth.

I had help by an old thread so I knew what to look for. Maybe not crystal clear exactly where.

http://forums.sohc4.net/index.php?topic=169359.msg1965282.msg#1965282

[PeWe]

Case threads and bolts check day.
I use Honda M6 bolts. Some with longer thread lenght just for sure. Rear bolts are strange. M8 in a hole for M10 since the head will sit too tight for socket.

From rear left, M8, M10 and M8.
K2 block with only M6 behind drive sprocket. 15, 25, 15 Nm.

I guess the left (close to final shaft with drive sprocket) M8 bolt with nut will handle 20Nm (grade 8.8 can 24Nm). The alu threads to the right on clutch side are fragile.

I use 12.9 allen head bolts for crank. Torqued 25Nm which is max the 1/4" torque wrench can. Allen head key for 1/4".

Engine will handle +85-90 whp range.

Ignition cover fits fine! No issues from an old damage that cracked the lower thread boss I repaired with JB Weld.

The cover is tightened by hand and shiny X-screws. I guess around 5Nm.

I'll continue to fasten all other covers to verify bolts and threads.  All covers will get allen head M6 which is easier to handle.

Oil pump and oil line threads must be verified too. Boring to find a bad thread late when most parts sit there. 

My brown K2 bike build has a bad thread for one oil line, quick fix with a longer bolt. It should have got a thread insert much earlier before engine assembly in frame.

I'll verify crank in with green bearings, tighten it to ensure no issues with cases and OK clearances.

When this is done, clean  cases inside as well as outside. Then paint the outside.

More work with not known parts coming together.

[PeWe]

The bosses for ignition plate are fine. Both tested plates sit tight, no movements sideways as my K6 and K2 bikes blocks had. I had to hammer them tighter.

If plate can move sideways, good luck adjusting the ignition, especially with points that will change point gap when the 3 screws are loosened adjusting 1:4. A never ending chain of adjustments.
I'm sure that's why people love the Dyna and similar. No issues if it slide a little sideways.

I forgot... I have NOS TEC points for that non TEC plate

I wonder if this will work? It fits fine though!

[PeWe]

I managed to find bolts in OK lenghts and torque test all covers.
No bad threads at all, tested oil pump and oil line adaptor threads too.
Here  with test covers. I'll use other covers.
The mission cover I'll use was too dirty so I tested a NOS cover that must come off asap before scratching it.

The alternator cover I'll use look very good. It has the electrical stuff mounted.

Next is to remove all covers, open cases and test crank clearances.
Then another torque test with crank in, rotating it freely at 25Nm tightened bolts to be sure about no bad findings too late.