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Discussion Starter · #1 ·
Hi All
I posted a thread back in September last regarding my smokey exhaust on my rebuilt CB175 K6
I decided to rebuild the engine again
I stripped it down and had the barrels rebored +0.75mm and got new pistons and rings to suit
I cleaned the head and valves and had two new valve guides put in the head (inlets) and the exhaust
valves checked for slop which the engineering shop said were fine
I put it all carefully back together.
Started it up and NO smoke until it warmed up. It then started to smoke a little. I assumed it was just the assembly lube !!
I took it for a 6 mile run round the town and found it was smoking on tickover a little
I have now done a 25 mile run keeping below 6000 revs and not lugging it
Smoking again but not as bad as before at this stage !
I pulled the plugs and did a compression test. 165psi on both cylinders (new compression tester)
I have just got back from a run of 54 miles and at tickover it smokes. Also up a long hill of approx. 11/2 miles it left a trail
of smoke
I have just checked the oil level and it is half way between the max and min marks !
Interestingly there is a drip of oil at the end of the oil breather pipe (new rubber pipe)
Is it possible that the head cover is blocked (although it has been cleaned at the first build stage) and
is building up pressure in the crankcase and blowing oil out past the rings into the combustion chamber !!
Any thought would be appreciated
voxy53
 

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Are the plugs oily or normal appearance? If the plugs are normal, pull the exhaust pipes off and check out the backside of the valves for evidence of oil leaking around the stems or around the od of the guides. If the plugs are oily, pull the carbs and check out the intake valves also.
 

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Discussion Starter · #3 ·
Hi mike
I will have a check today but I suspect the plugs will be oily as the end of the exhausts are black and oily !!
 

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If the engine was passing an amount of oil before, the exhaust may have some oil still in them, or a layer of oily carbon ala 2 stroke. Maybe this is what you are seeing, this "oily deposit" being burnt off??

I assume the pistons etc where oe not pattern ones as some of them can be "oil passers/pumpers". As long as the engine is not overfull ( any oil baffle plate in the sump on these, will check cmsnl ) and not too much oil is being flung from the big ends etc., and the rings are on the right way ( not upsidedown ), and the valve guides are good, and the crankcase ventilation system is all good, it may be just oil useage which will settle after a good running in?

How are the plugs, are they oily? and are the correct grade? I assume you do not add oil to the fuel.
 

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See cmsnl exhaust valve seals, some o rings involved....only limited time for a quick look on cmsnl, no oil restrictor jets seen, you have a lub diagram for thios engine??

is there a breather hole close to the rwear sprocket on these ala c90, its been a long time.......and i assume the head gasket is good as the cmsnkl exploded views seem to suggest the rear outer head studs are oilways to the head??

Again, littlehampton is in uk? i assume,,,,cb175k6 ss england?
 

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Discussion Starter · #7 ·
Hi All
I seem to be having a problem replying to this thread
I used genuine pistons and rings when assembling with the writing on the rings uppermost
I spent some time today checking the tappets, adjusted the cam chain and checked the compression after the 54 mile
run yesterday. 165psi on both pistons
The exhaust did have oil in from the previous build but should have burnt off by now
The plugs are oily and black
I started the engine up today and there was no smoke until it warmed up then it started at tickover
Blipping the throttle produced more smoke
When I switched off for a while and started it again no smoke for a while until it got hot
Oh and I don't put oil in the fuel
Pulling out the dipstick and you can get a rush uf air which I suppose is normal, also the breather pipe
blows air so is not blocked
Any ideas ?
 

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Discussion Starter · #10 ·
Hi
Thanks for the replies
Tickover may be a UK term but basically the engine speed with no throttle input
Also, yes I do live in the UK on the south coast
 

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Hi
Thanks for the replies
Tickover may be a UK term but basically the engine speed with no throttle input
Also, yes I do live in the UK on the south coast
'Tickover' = 'Idling' in US speak.

If the engine is burning that much oil, I'd be looking at the cylinder bores and oil control rings rather than the valve guides and seals. You've got good compression readings, but as we know, one way to check on low compression due to ring / bore wear is to put a teaspoon full of oil down the plug hole before using the compression tester. It sounds a though you've got plenty of oil there already.

Thicker engine oil won't help. Bitter memories of trying to cure an ancient Mitsubishi of its smoking habit, by adding Wynns Oil Treatment to the crankcase.

EDIT I take it is smoking on BOTH exhausts ?
 

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hope this works, pictures from oe cb175 honda manual including k6

P1010014.JPG P1010013.JPG P1010012.JPG P1010011.JPG P1010010.JPG P1010009.JPG

hurrah!! bit sorry they are sideways.

I assume you know about the oil pressure relief valve in the centrifugal oil filter "transfer" part, its sprung loaded and lifts with increasing pressure, if its stuck open then little to no oil pressure and if its stuck closed then no pressure "relief" meaning an over pressure condition.

Oilways to gearbox part all clears and not blocked, and you have seen the cmsnl exploded view to do with the valve seals??

Remove the exhaust and if you have an endoscope, see how much oily carbon there is in there if you can, but agreed, I would assume the oily carbon would have burnt off by know, but it can take time. Have know the exhaust systems to "decoke" themselves after a few hours of continued engine high ish revs even to the point of exiting sparks and the exhaust glowing red hot from the silencer rearwould, it does happen but that summer was hot and we had covered about 250 miles of 6k plus non stop! Its lucky we did'nt set Shropshire on fire that day!!

The exploded view does show no valve seal on the inlet but a few o rings etc on the exhaust, but thats "outside" of the combustion chamber.

No possibility of oil leakage into cylinder past the head gasket, from the rear outer oilways to the head?

You know you can "check" for oil flow to head via the rear outer head nuts being slackened a little.
 

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Discussion Starter · #14 ·
Hi drydreamer
Could you tell me what publication this is from as I would like to get a large copy of the oil circulation picture Fig. 74
 

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oe honda manual but that picture may be in the so hated on here clymer manual, will check when I get home. You think you have problems, dont ever buy a modern citroen car!!!!!

P1010006.JPG P1010005.JPG P1010004.JPG P1010007.JPG P1010008.JPG P1010009.JPG

The ground remains are from the hex head cam cover bolt that was corroded to nothing, but enough to stop the cam cover from being removed. Naturally it was one of the most difficult bolts to reach right at the back of the dohc engine. The vibe damper was not, it had un bonded its self from the cam belt sprocket.

The cam cover needed to come off as the camshaft ( exhaust ) is locked via a spanner and flats on the shaft, rather than a "holding tool" thru the rubber star gaps ( £130 new cam sprocket ) . These cars must be designed ( too much creative technology that only goes wrong ) and made by minions as there is little to no working room.

Anyways back to the cb175k6, you should be able to copy the picture, photo shop and enlarge, if not let me know and i can email to you a better one. The engine constrution picture would make for a nice calender or workshop picture/poster.

At least its not raining here today and that big yellow baloon is in the sky again!
 

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Manual states 170 psi compression figures, you sure no rings where broken when assembling the engine, its easy to do especially on non worn parts.
 

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I think the compression pressures depend very much on the tester used. With my Gunson gauge, I was getting 'only' 140 psi on a newly rebored engine, but it ran ( and runs ) fine, with no oil burning.

Agree about possible broken oil rings ( on both sides :eek:), also possible leak at the cylinder head end, but being a cynical chap, I do wonder if the place that did the rebore actually did it properly ?
 
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Discussion Starter · #19 ·
Hi All Thanks for the replies
I checked the ring gaps for all 6 ring before installation and they were all 8thou so I assume the bores are OK
I think I have said before that the smoking only starts when the engine gets hot
I have done an oil change and filter clean today with no problems visible I used Valvoline 10W-50 oil which
has made no difference to the situation (taking your point Richard)
Should I run it for 500 miles or so and see what happens ?
 

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I would - but remember, just because the ring gaps were correct, it doesn't mean the bore job was straight. Many less-than-correctly done bore jobs do not come out round, as I understand it, and ring tension on an area less than properly round would be reduced and allow blow-by and the oil that goes along with it
 
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