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Blowby Problem / Oil Leak


Rob36
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Hi guys. My mk1 Cavvy coupe (1900 cih) has had some issues spitting oil through the larger breather hose on the rocker cover into the carb. I tried to solve this by cleaning the gauze inside the rocker cover, and adding a brass union/small K&n type filter to the larger breather, thinking this may be a better solution. This was done just before the car was retired for the winter. For info, The engine also has some blowby - theres a definate 'chuffing' coming from the oil filler on tickover if you remove the cap.

This week i got the car out for its MOT since the weathers been ok. Its passed, but there was an advisory for an oil leak. I Drove it back to the lockup and, and once there I noticed right hand side of the engine is plastered with oil - I havent had chance to have a closer look as it was late but it seems possible that it may have been coming up from the dipstick.

Id be suprised if the mod to the rocker cover has restricted ventilation, but the dipstick thing would suggest it right?

Id been told that a bit of blowby was common for these engines and is not necissarily a problem, but it does seem to be the source of these issues!

Anyone had any similar probs? Anyone got any ideas that might help without a stripdown, which I havent really got the time and space for, and to be honest, that level of job would be stretching my knowledge!

Edited by Rob36
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Mine is "vented" down a pipe from the rear hole & breathes out under the car, somewhere.

Had to make the change once I whipped the Solex off for Weber/K&N setup.

Edited by plumster
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Interesting Plumster - I have a 32/36 DGV Weber, a brand spanker, sat there. Was gonna use it on a Civic for banger racing but never got round to it. Was it an easy switch? Presumably just an adapter plate and manual choke sorting yeah?

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Mine is "vented" down a pipe from the rear hole & breathes out under the car, somewhere.

Had to make the change once I whipped the Solex off for Weber/K&N setup.

The chassis oiler mod should have been done when new so we all had floors left :)

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Hi again guys. Ive had a little inspection of the car this afternoon. Oil splattering definately coming from the dipstick.

I checked out the top breathers - the larger one that goes to the air pan as standard (now leading directly to a small cone filter) seems to be breathing ok, BUT! the smaller front facing one isnt doing anything. There seems to be a blockage in the manifold. I probed it with a thin bit of steel and there does seem to be a bit of sludge in there. Gonna try a bit of carb cleaner on there when I get a moment - and will probably take the carb off for a proper clean. Is there a valve in there at all that could be gunked up?

Edited by Rob36
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I discovered something v strange today. I took off the carb in order to get at the 'blocked' nipple on the manifold (that the front rocker cover breather hose fits to) - and IT DOESNT APPEAR TO GO ANYWHERE! Theres no evidence of it whatsoever inside the manifold! Why would a rocker cover breather hose lead to a dead end on the manifold wall? If anyone could shed any light on this id be most appreciative, as at present Im no nearer solving this problem!

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Hi.the small breather pipe union on the manifold will be very small anyway.just a small air bleed.do not try to enlarge it thou.this will upset the mixture.secondly most times when oil comes out of the rocker cover breathers it means that the gauze inside is blocked.to clean it properly it needs removing by bending back the tabs and pulling it out.make sure you get it all out and cleaned thoroughly before putting it back.idealy put some new in or not quite as much as you took out.any major blow by after this will mean a badly worn engine. Only problem with the catch tank or pipe under the car idea is that it gives us classic drivers a bad name with the modern brigade because you can smell the breather fumes badly when following the car !

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ok thanks for the info Cam-in-head. Yeah, Id been doing some research - the smaller breather to manifold goes to a 'metered orifice' - as you say, a v small air bleed - apparently it does the same job as a pcv. I think mine must be blocked though as you cant suck in or out through the hose - and so small that I missed it on initial inspection! I shall have a closer look next time Im at the car. Regarding the gauze - I had previously cleanedit up & replaced it after soaking it in white spirit, but there was a lot of it in there. Ive now bought some copper gauze so Ill use that & see if that helps, hopefully if I do this plus locate/unblock the pinhole in the manifold, things might improve a bit!

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Removed the gauze today - It was a little gunked up, but not too bad, however, once Id removed it all, I noticed there was a rattling coming from insde the gauze housing when I shook the rocker cover. Some probing with various instruments then revealed no less that 5 old pieces of perished hose, some of em quite large! I expect that was restricting venting a bit!

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