Author Topic: New (to me!) '77 CB400F - US model  (Read 11836 times)

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #345 on: June 02, 2020, 11:55:56 AM »
Thanks for the input, guys.  I guess I can only try it and see what happens.

The history is as follows: I rode the bike in the summer of 2015.  It seemed to run ok then, decent power up to the red-line at least, anyway.  The PO rode it a couple hundred miles next summer, 2016.  It was stored in an unheated garage from the fall of 2016 through fall of 2018.  The guy who stored the bike said he drained the fuel tank, but not the carbs, and that he "kicked it over a few times" during that period, but I have no idea what that really means.  When I got the bike in 2018, I examined the dipstick oil and found it clean and clear, removed the plugs and squirted some oil in the cylinders, then kicked it over myself and found it to spin freely.  I buttoned it up and put it away.  It spent the winters of 2018 and 2019 in two different heated garages.

Stuck rings are certainly a possibility, the cause being rust also a possibility.  Just giving some recent background.  Wondering... how often does an engine's compression fail this badly, but also uniformly across all four cylinders simultaneously?

Offline Bryanj

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Re: New (to me!) '77 CB400F - US model
« Reply #346 on: June 02, 2020, 02:21:02 PM »
One big problem is the legth of flexible hose on the compression tester, i know you tried 2 testers but if they had about the same hose legth it could be your problem. The space left in head when piston at tdc is not much and could easily be doubled.
Thats one reason i say try it and see

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #347 on: June 02, 2020, 02:39:00 PM »
One big problem is the legth of flexible hose on the compression tester, i know you tried 2 testers but if they had about the same hose legth it could be your problem. The space left in head when piston at tdc is not much and could easily be doubled.
Thats one reason i say try it and see

Yes, that thought entered my head as well.  Both the testers I tried had similar 12-inch-ish length rubber hoses.  I've read posts espousing that effect on the US site, but I've heard other smart people reject that theory with arguments that sounded very convincing to me, partially ignorant as I am to the finer points of internal combustion engines.  I do find the uniform nature of my test numbers to be suspicious.

Is it a linear relationship?  If the tester is doubling the "compressed" chamber volume, would that imply a reading of one-half the normal value could be expected?

EDIT: I just tried the "thumb test" on cylinder #4 - did my best to get a good seal, cranked it over... it blows right by my thumb.  I folded up a "latex" glove to help get a better seal, and tried again with enough force to cause discomfort to my thumb... I may have been able hold against the compression, but not sure.  Does this suggest anything?
« Last Edit: June 02, 2020, 02:45:28 PM by mattsz »

Online K2-K6

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Re: New (to me!) '77 CB400F - US model
« Reply #348 on: June 02, 2020, 03:15:48 PM »
Where is the release valve on the test gauge?

As Brian says the tube will be part of the volume ( and give problems of reading) if the control valve is away at the gauge end of the tube as the tube volume is then evacuated at each exhaust stroke.

If valve is located right where the spark plug location is,  then the tube remains charged and should then report peak psi,  which should be close to specified data for the engine.

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #349 on: June 02, 2020, 03:19:19 PM »
Where is the release valve on the test gauge?

As Brian says the tube will be part of the volume ( and give problems of reading) if the control valve is away at the gauge end of the tube as the tube volume is then evacuated at each exhaust stroke.

If valve is located right where the spark plug location is,  then the tube remains charged and should then report peak psi,  which should be close to specified data for the engine.

The release valve on both the testers I used is located at the base of the gauge, not at the engine end.  I guess the volume of the gauge should be considered as well...

Online K2-K6

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Re: New (to me!) '77 CB400F - US model
« Reply #350 on: June 02, 2020, 03:44:38 PM »
Looks like your error is there.

Just a rough guess from generally available gauges would suggest pipe volume similar to combustion volume above piston.

Shot in the dark estimation,  150 psi true effective reading would be somewhere near current status  ;D that's my first "range finder" any advances ?

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Re: New (to me!) '77 CB400F - US model
« Reply #351 on: June 02, 2020, 03:53:54 PM »
For reference,  I've had this type for more years than I care to remember

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That tag showing at the end is the Schrader valve to reset the gauge and evacuate the previous pressure. Bit of a pain to use,  no sophistication as you have to hold it in tight and get someone else to crank it if you can't reach the button. But always reliable.

Offline Nurse Julie

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Re: New (to me!) '77 CB400F - US model
« Reply #352 on: June 02, 2020, 04:03:05 PM »
I have seen someone in the USA test for equal compression across all four cylinders by dropping the exhaust headers off and placing a ping ping ball (table tennis ball) in each exhaust port. Crank the engine over on the kick start and if all the balls hit the garage wall at the same time, compression was close enough to equal to not worry about it 😁😁😁😁😁
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #353 on: June 02, 2020, 04:06:18 PM »
I have seen someone in the USA test for equal compression across all four cylinders by dropping the exhaust headers off and placing a ping ping ball (table tennis ball) in each exhaust port. Crank the engine over on the kick start and if all the balls hit the garage wall at the same time, compression was close enough to equal to not worry about it 😁😁😁😁😁

 ;D

Equally low is my concern...

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #354 on: July 01, 2020, 11:51:46 AM »
Ok, so I've decided for the moment to deal with the possible low compression using an old tried and tested tool: denial.  I'll revisit the issue if I find problems with it after I try to get it running.

I've moved on to the oil - draining it, specifically, to inspect and clean the oil pan and strainer, and also to remove the clutch cover and examine the release mechanism (the subject of another thread).

This job has progressed like most of the others - the drain plug must have been last installed by Eddie Hall.  I needed quite a long breaker bar extension to loosen it; remarkable, really, that the threads were never stripped.  What I assume is an aluminum washer on the plug seems to have been crushed so tightly that it and the plug are now permanently joined...

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The oil filter bolt has been abused - but it wasn't overly-tightened, and a 6-point socket fit it and removed it easily...

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« Last Edit: July 01, 2020, 12:06:27 PM by mattsz »

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #355 on: July 01, 2020, 11:58:11 AM »
While the old oil that I could see (lifted on the dipstick, pumped up to the cam shaft when cranking the engine over) looked clean, I found it wasn’t really so.  The drained oil was pretty black, as was the filter.  The filter cover had some dark residue settled in it - bearing material?  combustion products?  both?

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The oil pan itself came off easily, no overtightened bolts.  Of course, I couldn’t access them all with the exhaust in place, so the headers had to come off (except for the common surface rust around the tops, the rest looks good, including the collector).  There was a fair amount of the dark residue in the pan as well; not sure how it compares to some others I’ve seen… recall the bike shows 26k miles, and the cam shaft bearing surfaces look pretty good - haven’t laid eyes on the crank bearings though…

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« Last Edit: July 01, 2020, 12:08:56 PM by mattsz »

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #356 on: July 01, 2020, 12:01:49 PM »
I dredged the oil pan muck for debris - here’s what I found.  The flecks on the rag remained after the black oily residue soaked in - metallic looking, but seemingly more like paint flecks:

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The pieces above the rag are proper metal shards:

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There isn’t any obvious evidence that the pan has been off before - except for one strange thing: near one of the mounting holes for the “oil separator plate,” there’s some spiral skip marks which look like someone was trying to drill the hole and allowed the bit to wander off… twice!  I can’t imagine that would have happened at the factory… but why would anyone be waving a loaded drill bit in that direction?

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« Last Edit: July 01, 2020, 12:12:45 PM by mattsz »

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #357 on: July 01, 2020, 12:04:36 PM »
Finally, the oil pan appears to be cracked (hmm... thumbnail upside down again?):

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It’s not, however, in the “usual” spot, around the drain hole.  Plus, no matter how carefully I look, I can’t see any evidence of it on the inside:

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Is it possible that there’s some sort of fracture that doesn’t go clear through?
« Last Edit: July 01, 2020, 12:14:16 PM by mattsz »

Online K2-K6

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Re: New (to me!) '77 CB400F - US model
« Reply #358 on: July 02, 2020, 09:20:58 AM »
The shrapnel looks slightly concerning,  that piece of an arc appears to be heading toward 20/25mm diameter and at a preliminary guess could be something from the gearbox.  Are you continuing to strip motor?

The sump "crack" you could tip it at a slight angle and put petrol into it to above the crack line to see if there's any pathway through it. Generally a crack in casting will pass all the way through it even if pinched tight on opposite face,  I'd suspect it would need attention all things being equal.  Cleaning with a solvent prior to getting it Tig welded would probably be a decent solution,  and leave the weld seam in place,  not ground off.

The sump looks almost as if the bike has been lifted by jack on the sump plug at some point,  not the usual clobbered on the ground that's often seen.

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #359 on: July 02, 2020, 12:05:36 PM »
Thanks K2-K6!

If it matters, the curved piece appears to be more like a 12mm diameter rather than 20-25mm...

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... but to be honest, when examining it closely from all angles, it looks more like a curved shaving rather than a broken piece pre-formed at that arc.  I was not planning to strip the motor at this point, I intended to see how it runs first!

(FWIW, that pile of rubbish looks very much like what came off the oil strainer during my 2011 Royal Enfield's first oil change!  ::) ;D )

I'll leak-test the sump once I get a new plug washer...

 

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