Author Topic: CB550K - engine rebuild (partial or full)  (Read 2065 times)

Offline Erny

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Re: CB550K - engine rebuild (partial or full)
« Reply #75 on: February 23, 2021, 07:43:47 AM »
Thanks Bryan!
CB750K7 US model (1977)
CB550K1 US model (1975)

Offline K2-K6

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Re: CB550K - engine rebuild (partial or full)
« Reply #76 on: February 23, 2021, 12:51:41 PM »
As Bryan says,  all ok.

To take it underneath that which is needed for good mechanical condition, it can tell us more about the conditions during running so far.

The outer two bearing surfaces show just a flattening of the original boring marks and exactly as you expect to find as witness marks.

The marks are consistent with the design in that the bore size has to have a tolerance in relation to the camshaft journal that avoids seizure and allows for oil film effectively not under pressure.  You can see from the wear marks how far up the "wall" of the bearings that the two depart and no longer touch each other. 
The centre two bearings show their witness marks travelling further than the outer two,  a little like judging plastiguage. Meaning the camshaft has worn into the bearing further on these two,  but a very very small amount.
This would happen if the oil film was unable to support the load as it should. Mostly this is associated with oil condition and specifically dilution/service interval in the engine's life so far.

It seems consistent with the amount of wear in the primary chain too. Those bearings (within the chain) are possibly the highest loaded individual parts in the engine with their lifing giving a good indicator initially of running conditions to that point.

As first stated, it's perfectly normal to see the bearings in the head like this and it's not a fault as such in the overall condition,  just that you can have more of a picture of progress so far in the engine's life.

Offline Erny

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Re: CB550K - engine rebuild (partial or full)
« Reply #77 on: Today at 12:26:28 AM »
Small update on my side.

Took carbs and pipes off and did again leak test under these conditions: measured cylinder was in TDC, input pressure ~22psi as per leak tester manual.
result - all cyls:
- shows approx up to 10%-12% leak
- all IN and EX valves are tight (no air or sound goes off intake or exhaust port), air is leaking and is audible around cam chain and oil dipstick, so leaks past the rings (?).

With great weather over last days, I started to consider changing strategy - just fix valve cover, cam and rocker issue and keep riding bike this seson as is. Rebuild (partial or full) can be done next winter.

Before putting bike back to road, I'd like to test oil pressure - where people connect manometer to measure oil pressure? What fitting / tool I shall look for?
CB750K7 US model (1977)
CB550K1 US model (1975)

Offline Bryanj

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Re: CB550K - engine rebuild (partial or full)
« Reply #78 on: Today at 12:38:04 AM »
Thats not a high percentage so should be ok when running as combustion pressure gets behind ring and increases tightness to bore.
For oil pressure either remove the pressure switch and screw an adaptor in there or you have to drill and tap the hexagon "bung" below the points cover

 

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