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| SpannerMonkey |
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SpannerMonkey
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 Posted: 21:57 - 18 Apr 2011  Post subject: Silly question guys... |
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But do ALL 4 stroke engines have a crank-case breather? my PC50 keeps chucking oil out of a hole in the top of my engine in fair quantities. At first I thought my Crank-case gasket had gone, but someone pointed out it may be coming from a breather. My haynes manual makes NO mention to a breather at all and there is no fitment for a breather pipe, just what appears to be a hole in the top of the engine. Oil has only recently started coming out of it since I've topped it up (Yes I've topped it up correctly)
https://i138.photobucket.com/albums/q262/Snaphappyalex/Honda%20PC50%20stuff/DSC00043.jpg
https://i138.photobucket.com/albums/q262/Snaphappyalex/Honda%20PC50%20stuff/DSC00041.jpg
As you can see, it's right at the top of my engine in the centre. any ideas?
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| N cee thirty |
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N cee thirty
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SpannerMonkey
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| N cee thirty |
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SpannerMonkey
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| bass2k8 |
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bass2k8
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| Posted: 23:11 - 18 Apr 2011 Post subject: |
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This is very interesting mate  I'd love to know more... Could you post some more pictures of your PC50 in the gallery section in the forums?
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| N cee thirty |
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SpannerMonkey
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| N cee thirty |
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SpannerMonkey
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| bass2k8 |
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bass2k8
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| Posted: 23:44 - 18 Apr 2011 Post subject: |
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Thanks, I would love to have a go on one of them  ... They look awesome. Seen that the carb bowl (I think) had a LOT of sediments, never seen it that bad haha. Thats 30 years older than my ped, and I thought mine was old! haha.
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N cee thirty
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| Posted: 23:45 - 18 Apr 2011 Post subject: |
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hmm i'd say the gaskets just knackered 
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| Teflon-Mike |
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Teflon-Mike
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Posted: 02:08 - 19 Apr 2011  Post subject: |
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Spanner... lets think about this one..... you have a piston going up and down in a cylinder.
Beneath that cylinder is the crank case.
If the crank case wasn't vented some how, then the piston falling in the cylinder would pressurise the crank case like in a two stroke, and as its a near horizontal engine, that means?
The pressure would in all probability try squashing the oil past the piston rings into the combustion chamber.
some engines dont have breathers. If the crank case is particularly huge in relation to the cylinder displacement, and they have enough pistons that one going up will be balenced by one coming down, to minimise 'windage'.... but I doubt that your motor is unvented....
So sounds VERY much like the old over filled oil 'niggle'....
You say you DID fill correctly.......
But lets check.
1) did you completely drain the sump of old oil?
2) how did you measure the 'fill'?
If you filled by set volume, book normally gives two different quantities, one for a 'dry' engine which has no oil in the sum at all, and has the iul pimp and filter 'drained', another for an oil change, which presumes the engine has a residual amount of oil in it in the sump, filter and pump.
3) dipstick screwed in, or dipstic rested on top?
If you measured to a dipstick rested on threads, and its supposed to be screwed in, possible that you have over filled.
If all these perms can catagorically be discounted.....
Then excess crank case pressure.... usually means knackered bore/rings.... also usually accompanied by lots of oil burn after oil change / top up.
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SpannerMonkey
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Teflon-Mike
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| Chriss |
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Chriss
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| Teflon-Mike |
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Teflon-Mike
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| Posted: 14:51 - 19 Apr 2011 Post subject: |
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| Chriss wrote: | | Teflon-Mike wrote: |
If confident on that lot, then rings & blow by! |
Wouldn't a compression check be the quick way to check this? |
Depends. First you would need a compression tester.
Next you would need to have an adaptor for the wampy small plug thread honda use, esp on thier little bikes.
Then it would tell you if you had compression in the pot, or not...
Wouldn't tell you WHY you don't have any, if you don't.
Could be stuck valve, tight valve clerances, valve seat pitting, burned valve, etc. Head Gasket failure. Holed piston. Cracked piston. Cracked rings. Worn or scored bore, pourouse cylinder.
Basically anything that lets pressure out the pot......
Most often HGF, valve seats or worn bores.... but not definative.
Also with high crank-case pressure, from blow by, engine might be making enough compression to give a good reading on a compression tester... and on a single, you cant get any sense from different readings on different pots..... and only blowing by the rings when you have combustion pressure in the cyliner, which is obviousely an awful lot higher then the 150psi or so you might get cold cranking.
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Teflon-Mike
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| Posted: 15:05 - 19 Apr 2011 Post subject: |
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| spannermonkey91 wrote: | | Teflon-Mike wrote: | Rested on top is th moreusual honda way....
Is teh dip stick the right one?
If confident on that lot, then rings & blow by! |
If I'm honest, the dipstick looks slightly bent... But not dramatically.
I cant say I'm SURE it's the right one, But it seems to match up with the one in the haynes manual. |
OK.... this is an old engine.... very old engine.
You planned a strip anyway, right?
Lets thing about this.
Running as is..... be tempting to dibble or pippette some oil out the crank case, and see what level you have to go down to until it stops venting.... or your not brave enough to remove more oil!
You may be getting falce reading.
alternatively, completely drain (again), then go by sump capacity, on refill, BUT short fill it to account for residual & priming.....
Whats the Haynes say the 'Dry' sump capacity is?
I'd do a rough reckoner, and short it something like 50cc or 10% +25cc, depending on what the capacity was. See what kind of level that gave me on an improvides dip-stick.
Then run & check for vent.
If you are still getting venting, then high crankcase pressure can only come from two other sources, after high oil level.
Blow By, past the rings, pressurising teh crank case with combustion pressure.
Over active oil pump......
I believe its the C90 /CG 'centrifugal' oil pimp on that, isn't it? Drum on the end of the crank, bottom half sat in the sump, lifting & chucking the oul out to get oil pressure fro teh centrifugal force inside the drum....... ie effall! Its a lay down single, that dont need much oil pressure, almost splash lubed, and with no great 'height' the oil needs lifting to get the oil from the sump to the rockers....
NB.... its not very likely that that kind of oil pump, on that kind of engine, is going to be creating SO much excess oil pressure its venting the stuff out the breather......
Which?!?!?
Leads you to where?
RINGS / BORE
Old motor.... though at one year younger than me, I HATE to say that!..... low miles, its been sat for many many years.
Probably with the iron rings, 'dry' in the ali piston, in steel bore.
Liklihood that the piston ring grooves have firred up, trapping the rings, is high, if not likely that the corrosion is preventing teh rings seeing pressure to splay them against the cylinder wall. Likely that the rings have corroded at the top, where they dont have drip lube from teh sump, AND with corrosion in teh ring grooves aren't 'rotating' in teh ring grooves to 'self clean'.......
In short, very good chance that if you wip the head and barel off...... without having to do a full strip, you might find that you only have to clean the piston, and or replace the rings........
BUT, more investigation needed.... I'm GOOD (he says modestly!) but not THAT good, I can diagnose a bikes maledies by telepathy!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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| SpannerMonkey |
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SpannerMonkey
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| Posted: 15:55 - 19 Apr 2011 Post subject: |
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| Teflon-Mike wrote: |
see what level you have to go down to until it stops venting.... Till way below the minimum as it was slowly venting oil below minimum before, but not when I first got the bike. it wasnt dripping ANY oil when I first got it.
alternatively, completely drain (again), then go by sump capacity, on refill, BUT short fill it to account for residual & priming.....
Whats the Haynes say the 'Dry' sump capacity is? it just says 750ml under oil capacity, doesnt give me a dry sump or anything reading
I'd do a rough reckoner, and short it something like 50cc or 10% +25cc, depending on what the capacity was. See what kind of level that gave me on an improvides dip-stick.
Then run & check for vent.
If you are still getting venting, then high crankcase pressure can only come from two other sources, after high oil level.
Blow By, past the rings, pressurising teh crank case with combustion pressure.
Over active oil pump......
I believe its the C90 /CG 'centrifugal' oil pimp on that, isn't it? Haynes says Trochoidial type oil pump although I know the connecting rod has a hook on scoop on the big end that aids to splash oil
Which?!?!?
Leads you to where?
RINGS / BORE
Old motor.... though at one year younger than me, I HATE to say that!..... low miles, its been sat for many many years.
Probably with the iron rings, 'dry' in the ali piston, in steel bore.
Liklihood that the piston ring grooves have firred up, trapping the rings, is high, if not likely that the corrosion is preventing teh rings seeing pressure to splay them against the cylinder wall. Likely that the rings have corroded at the top, where they dont have drip lube from teh sump, AND with corrosion in teh ring grooves aren't 'rotating' in teh ring grooves to 'self clean'.......
I seem to recall this being called Bimetal corrosion and being number one cause for seized classics... Not sure if I'm right on that. What I'm struggling to understand is how it can be doing it now, But not 2 weeks ago, surely I would have had this issue from day 1 of ownership if rings were corroded in place
In short, very good chance that if you wip the head and barel off...... without having to do a full strip, you might find that you only have to clean the piston, and or replace the rings........
BUT, more investigation needed.... I'm GOOD (he says modestly!) but not THAT good, I can diagnose a bikes maledies by telepathy! |
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| Teflon-Mike |
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Teflon-Mike
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| Posted: 18:12 - 19 Apr 2011 Post subject: |
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| spannermonkey91 wrote: | Till way below the minimum as it was slowly venting oil below minimum before, but not when I first got the bike. it wasnt dripping ANY oil when I first got it. |
~So something has freed up, or shifted, then.... Hmmm....
| spannermonkey91 wrote: | Whats the Haynes say the 'Dry' sump capacity is? it just says 750ml under oil capacity, doesnt give me a dry sump or anything reading |
Thats quite a bit of oil for a little engine, it could probably run with as little as half a liter in it.
so it has a tricoidal pump, eh? That could deliver a bit more pressure...... but not top of my list of suspects.
| spannermonkey91 wrote: | I seem to recall this being called Bimetal corrosion and being number one cause for seized classics... Not sure if I'm right on that. What I'm struggling to understand is how it can be doing it now, But not 2 weeks ago, surely I would have had this issue from day 1 of ownership if rings were corroded in place |
Technically its electrofrelytic corrosion; different metals have different electro pottentials setting up a galvanic 'cell'....... but yeah!
Two weeks is not a term an engine understands.... how much 'run time' has it had?
Early running, the rings pressed against the bore under natural tension, and 'stuck'.... possibility 'use' has scored the bore.....
More LIKELY..... stuck ring, under use has actually snapped......
Its a push rod motor, isn't it?
Head off, inspect that barel.
Barel off, look at the piston.
There really cant be much else that would cause such a high crank case pressure.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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SpannerMonkey
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