Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: 400 Cafe Racer on May 19, 2021, 04:45:09 PM
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Hi Guys,
I mentioned when congratulating Nurse Julie on her Engine Rebuild thread, and on my "Splitting the crankcase problem" thread, that I was was going to investigate a mechanical "Screech" sound that lasted for several seconds after resarting the bike while it was warmed up after my second ride.
My hunch from my experience, was that it sounded like the main bearings were tight and could seize up if not rectified.
Recent History
The PO had carried out a full engine rebuild with the majority of work done by an engine specialist (THIS WAS NOT TRIG AND JULIE I must emphasise), just leaving the PO to do final assembly. This work was done in 2015 and the engine has run 3000miles since. Advice on which shell sizes to use on which journals was made by the specialist.
Having experienced the noise I consulted the PO who thought it might be the timing chain adjustment, but this "Screech" sound was far too solid and friction sounding to ignore. I decided NOT to run the engine again and do a full strip and inspection.
Having just split the casings and inspected the journals and shells it looks as though the centre bearing has been the main offender with journals 2 and 4 not far behind. See photos. In the order of 1 to 5.
It was noticeable that 2,3 and 4 had little oil film on the crank or the shell (oil squeezed out due to lack of clearance)and you will see the highly polished face on these journals and shells. Compare these with 1 and 5 which are relatively unpolished and wet with oil, showing that a good hydrodynamic film of oil was present to "float the bearings" 1 and 5 rather than grip them.
I think this has only shown up because of the heat sinking and oil draining from the heads and barrels after a ride causing the extra heat transfer and differential expansion on these components at the time, and the fact I started the engine again shortly after.
Journals 2,3 and 4 will now come under closer scrutiny with Plastigauge measurement to see the actual clearance measurement.
To be continued as time allows.
Dennis
PS my next post will show the Shells 1 to 5
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Shells 1 to 5
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Have you inspected the camshaft bearings yet?
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Hi K2-K6,
Yes thanks,
The camshaft bearings, Camshaft, Cam followers/rockers and all valve gear all appear to be near pristine condition. I think the lubricity of the oil along with regular changes have resulted in no replacements needed, as was the case when the engine was rebuilt by PO. The only minor flaw I can see fnom initial inspection is that when the cylider head cover was refitted at some previous point, the operative did not engage the teeth of the rev counter drive gear by "feel" while progresively tigtening down the cover. This has resulted in some minute chipping of the camshaft teeth edges of the worm drive. This looks as though it was dressed off and has been used without further problem. There are no marks on the cable drive gear.
I believe one of the main reasons for rebuild at that time was someone before had insalled an oil scaper ring badly, this caused a wear groove in the bore, which resulted in a new liner being fitted on the rebuild by PO.
All pistons are marked HONDA.
Thanks
Dennis
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Hi Oddjob,
Thanks for your input and the important points you make, which I will check out. I will possibly get time tomorrow to lift out the crank and do an inspection behind the shells to examine further.
In general everything seems very clean internally with no particulate matter visible. No bits in the oil filter or pump pick up screen. Pistons seem rather sooty, with just a hint of slight leanness (white carbon fringe) on the edge of No1 Exh valve edge and centre electrode. There is probably some fine tuning I need to do later. In general it seems to be set up slightly rich and was running between 12.4 and 12.7 A/F ratio on the Inovate A/F gauge.
During the "Screech" time you could feel the vibration "grab" of the crank on the shells. Luckily it has not resulted in spinning a shell. I shall measure up the crank and examine closer when I get more time to fully assess if there is any refacing needed. Everything will get a detailed assessment in due course as I want make sure all is order when I rebuild.
Due to family circumstances I am coming to a busy period and it may be several weeks before I can get back to it, so apologies in advance for delay on the findings or outcome.
PS
I have decided not to lift the crank out at present and disturb any "Evidence" associated with the cause, but rather do the Plastigauge measurement with everything "as is" to capture true measurement of the clearance before anything is moved. This should help identify what clearance currently exists on a cold engine and how much thermal expansion has caused the crank to tighten. I believe that this could be quite valuable for future reference. Given the configuration of the engine design, the 2 inner cylinders on the air cooled block are always going to run hotter.
Thanks
Dennis
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The only refacing you can do on your crank is micro polishing. No regrinds are possible.
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Hi Roy,
Thanks for your input. Yes, from the other posts I have read I understand that a crank grind is not possible. By "refacing" I meant carrying out any fine polishing evenly around the 3 journals, that would be after detailed close up examination and measuring for any possibility of uneven wear or ovality.
Thanks ;)
Dennis
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Ref: Hondabond. Just looking at the threaded holes on a Triumph Crankcase to decide whether they will take the screws holding the Primary Chaincase Cover or not. They won't, and two screws were broken off inside the blind threaded holes. Out with the grinder as it was impossible to extract the broken screws. Got a fair way down and I was able to remove the remains of both broken screws.......so I can salvage the cases by welding them back up and re-tapping the holes. The reason the screws had broken is that each hole had a goodly dollop of 'Hondabond' bunging up the bottom of each blind hole and as the screws couldn't be tightened any further because of the 'pistoning' effect, the Orangutan PO had given them a bit more welly and they had snapped off. FFS.
Some monkeys shouldn't progress from peeling bananas and scratching their arses in public just so that little Kids can have a good laugh.
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Imho looking at your shells I can't see them being the cause of the noise you describe - the shells do not look too bad especially if they are original and were not replaced by the PO.
I would have expected some serious 'picking up' of the bearing surfaces if they were too tight.
Maybe as you say its just lack of oil pressure that caused the rumble but even then on a 5 bearing crank that sounds somehow unlikely in my automotive experience - its always difficult to describe & diagnose engine sounds. - except when your big ends clatter!
It will be interesting to see what your Plastigauge check reveals in due course.
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Hi MCTID
I took the decision I described to Ted, which I have used for years on all sorts of gasket pastes, that is to use cellulose thinners to soften and liquidize to get it out.
Pour a little down the blind hole, let it soak for a while, thread the bolt into the casing and gently wind down, make sure you stop when you meet resistance.
At this point, imagine you are tapping a thread with a thread tap. Turn the bolt gently for a quarter turn then turn it backwards a half turn to clear it. Carry on gently with this method and you will find the dissolved gasket goo is pushed out of the top of the thread. I used this method on 4 affected threaded blind holes. They all cleared and it took me about 45 mins.
I can understand your frustrations with excess use of Hondabond. I measured the depth of the casing the bolt was clamping, then threaded the bolt into the blind hole to see when it met high resistance to turning (bottoming onto the Hondabond) it was evident that you would have the situation you described, so I would recommend the above.
Dennis