Topic: CB550 Top End Rebuild

[CJK]

It all depends. How deep are the pistons sitting below the deck when assembled? How tight a squish band do you seek? I used the 0.040 with a final squish to 0.032, but I had the deck milled until the pistons were sitting just about dead flush (they were 0.032 in the hole). Don’t forget if you mill the deck, the locating dowels need to be trimmed else they will suspend the head.

Cal,

I haven't assembled it yet. So if my understanding is correct, the critical measurement is the piston TDC to chamber because that affects both clearance but also the volume of the combustion chamber? What is the actual measurement that I'm trying to solve for?

Since I know 0.004" was removed from the head, the variables that I can alter to end up with the proper measurement are:
- head gasket thickness (course adjustment 0.030", 0.040", and 0.050")
- amount of material removed to deck cylinders


Process:
1) Re-assembled cylinders with pistons
2) Measure height of pistons in cylinders at TDC


Should I be concerned with using a new, uncompressed base gasket between cylinders and case?

[CJK]

Head arrived back from MReick completely rebuilt and what he called a “Stage 2.5” job.

Ring end gap measured and set as per Wiseco Specs. Pistons assembled back in the cylinders and connected to rods.

Next, I need to measure across the top of the pistons to determine gasket thickness.

The pictures below are with the pistons at TDC.

I did an initial measurement but what it was getting late so I was rushed.

Where should I be measuring the piston? At the center or the edge?

Is my measurement method correct or should I be using a flat ruler across the top and a feeler gauge?







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[CJK]

I’ll be running a CB650 Camshaft, which from my memory provides increased duration but no additional lift.

I think the engine clay clearance is a solid idea. I’ve already invested enough time and money to do it right, might as well continue on the path rather than shortcut and risk damage.

[CJK]

That would make sense why I’m measuring about -0.010” from yours (assuming you haven’t had any material decked).

Head -0.004”
Cylinders -0.005” (by Recollection)

I just watched a YouTube video on the clay method. I’ll order both 0.040” and 0.050” MLS gaskets. Does any company make spacers that are are like 0.005” (to use as like shims)?

EDIT:

It seems only Dynoman has 0.040” and 0.060” thickness 59/60mm gaskets.

[CJK]

I did install the base gasket supplied with the Vesrah kit, but have not yet put the head on or torqued anything down. I used a dead blow mallet to gently pound down the head to seat it.

Thinking about it, when talking about thousandths, that could affect the measurements.


I’m a little confused as to your last comment for next steps, you would recommend ordering a 0.040” MLS Head Gasket?

Or I should assemble head (without a HG) and torque to spec to squish/seat the cylinders/head, remove head, then measure for final depth?

By the way, the MotoGP pipe will sound and work well once it’s all back together!


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[CJK]

I suspect an 0.040 will be just fine unless you mill the block more (unnecessary). Torque everything down with clay on top of pistons. Rotate the cam to get your clearance. Remove head. Then you’ll know which gasket to get.

Roger, will do it on Saturday! Thanks Cal.

[dave500]

I put xl125 pistons into a cb500 once,the xl are domed,gotta check clearance,standard cam on this motor was fine,my 550 still hauls better than this did with flat tops!

[CJK]

Ok, one step forward, and I’m stalled again.

Cylinders, cam chain tensioner installed. Then I installed the head on top of cylinders with dowel pins but no HG. The pins won’t need to be trimmed at all as the head and cylinders mated together perfectly.

After that, I torqued the head down to spec (after using tap and die to clean stud and nut threads). Then installed CB550 cam with the CB550 Cam sprocket.

To ensure I didn’t bend any valves, I backed the  rocker arm tappets all the way out as well as used the rubber band trick to hold the rocker arms up.

The problem I am running into is when I place the valve cover on, whichever lob is at TDC is pushing the cam shaft all the way down to the valve stem. In order to torque the valve cover down, I would have to keep tension on the valve stem and there would be 0 tappet clearance




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[bryanj]

There will always be valve(s) that are open at any point of engine rotation, as long as the adjusters are not pushing the top of the valve stem sideways you are good to go.

[CJK]

Thanks Bryan and Cal, I’ll give it a try right now


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[CJK]

Piston to Valve clearance completed using the clay method.

Without any HG, the Intake clearance was 0.100” across the board and the Exhaust was 0.065”.

I would assume a standard thickness MLS HG (0.040”) would be appropriate. 

[CJK]

Well the MLS head gasket and adjustable cam sprocket arrived from DynoMan so was finally able to begin final re-assembly. I used assembly lube in the cylinders, installed HG and torqued down the cylinders to 15 lbs.

Then I installed CB650 Cam + CB550 Adjustable cam sprocket, + more assembly lube on the journals, and cam lobes. Set 1-4 to TDC, and secured the sprocket to the cam with the notch parallel to head surface.

All was going well, all the screws were going in, then it was time to begin torquing them down the 0.8-1.2 kg/m (I set torque wrench to 7 ft lbs). I started evenly and in the center, similar to process for torquing down cylinder head nuts.

I made it to the second bolt of the center 4 under the breather cover and the bolt sheared off in the head. I wasn’t at 7 ft lbs, yet so really I just got unlucky with an old bolt. My fault for re-using old hardware. The bolt is 10mm head, 5.25mm shaft diameter.

My question is...now what? Any recommendations?

I’m currently sipping Japanese whiskey, and walked away from it for the night because I’m pretty upset and hoping I didn’t ruin the head Mike modified for me.




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[flatlander]

just take that cover off again and see what you got. depending on how it broke off, there are different methods to get it out. if you're lucky you can just grab it with some pliers and turn it out. if it's too far down you could use a small sharp chisel, gently tapping it to turn the bolt out. post a pic of it here and people will give you more advice how to remove it without causing damage.
anyway, the head is not ruined. the bolt just needs to get out.

[dave500]

ive said it before and ill say it again never torque any 6mm bolts down.

[CJK]

Thanks Flatlander, Dave and Cal. I’ll pull the valve cover off after work today to take a look.


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[CJK]

I took the valve cover off to look at the bolt.

Thankfully, it doesn’t look too bad. It did shear off above the hole so I have something to with.

I’ll be ordering 4 new bolts (M6x1x32.5mm) to replace all of the center bolts. I have stainless steel bolts for all the other valve and breather cover hardware. The center (4) weren’t included in the kit.

I may be able to grab it with vice grips. If not, I might be able to grind a small notch in it, and unscrew it with a flat head.

Any other ideas I’m missing?




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[bryanj]

Hopefully not bottomed and will turn out easy. Pretty blue pucks, not seen those before.

[CJK]

Hopefully not bottomed and will turn out easy. Pretty blue pucks, not seen those before.

I hope so, too. I’ll take a crack at it Saturday morning.

I was expecting black ones, but they fit and feel nice. I got them from 4into1, which is local to me.


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[dave500]

ive said it before and ill say it again never torque any 6mm bolts down.

Nothing wrong with torquing 6mm bolts, just crappy hardware. The "torque value" is so low for a 6mm that "firm and hand tight" is plenty, absent of a torque wrench.

torqueing 6mm not only risks snapping bolts but moreso stripping the soft alloy thread they go into,just nip them down they aint wheel nuts.

[addictedtocafe]

I think a dremel notch in the center and an impact screwdriver might be your best bet.

I don't like torquing m6 bolts either - and I have had lots of failures of original hardware. All new bolts in that size for me, these days. In fact, if it isn't a specialty fastener (IE washered nut, or special non-standard sizes), I replace all hardware.  FWIW

[CJK]

Thanks, all. I’ll be removing the cam and head tomorrow so that I can work on this. I think I’ll try Cal’s idea of tacking the nut first because worse case there’s no damage. If that doesn’t work, I can still grind a notch into the bolt and unscrew.

I think the lesson learned from me is that 1) Use new hardware as cheap insurance and 2) While you *could* torque these bolts down to 5 ft lbs as Honda recommends, hand tight is sufficient and much less risk of destroying the soft aluminum threads or shearing small bolts.


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[CJK]

Good news: after removing the cam, I was able to grab the threads with needle nose pliers and unscrew the bolt.

After that, I reinstalled the cam, then used non-hardening gasket material to seal the pucks in place (following along in Hondaman’s book. I cleaned it all up and put the valve cover back on and hand tightened all the bolts

Tappet adjusted to spec and the engine is back together. I noticed my timing mark (T - F) for 1-4 is slightly off TDC (5-10 degrees).

I set the cam timing based on piston 1-4 TDC, not the timing plate as I noticed it was off at that point. From what I remember, I can bend springs to adjust the timing plate to the proper location.

Exhaust headers (MotoGPwerks courtesy of Cal) with SS spigots were installed.

Next step is to finish cleaning carburetors to be spotless, then put them back on. With the JMR Stage 2.5 head work, CB650 cam, the MotoGPWerks exhaust, port matched intake runners and TinTop Anti-pod filter, I think this engine should breathe nicely.

Living at sea level, I think I’ll start jetting at 1 size up from Stock specs. My beginning thoughts are #40 Slow Jet, Lift needle +1 notch, #105 Main.

Any other thoughts/recommendations?


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[CJK]

Carb settings should be VERY close as you describe them.

Awesome! Thanks for confirming my thoughts.

I’ve learned from reading the many threads, where the person overestimates how much fuel is actually needed. The classic case of thinking more fuel = more power.


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[RAFster122s]

Any updates to share Chris?

[CJK]

Any updates to share Chris?

I wish, I had to come down to 29 Palms for two weeks for military work so that hindered me.

Everything is back together.
Carbs are bench-synced. 
Static timing is set.


So next step is to gas up the carbs and get it running, then carb tuning and dynamic timing.

I do have an adjustable cam sprocket that I wanted to advance the timing in the future, but I wanted to get it running nicely before I do that so I have a reference point. I still need to get a degree wheel to do that.


I ended up putting 100# mains in the carbs. I realized I didn’t have 105# so I’ll order those.

I anticipate having it running by the weekend of 22-23 June. Bummer because I wanted to be riding around, but it’s been a long term project anyway so I’d rather not rush an imaginary timeline.



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