airbox breather thingy...

[peteA]

The collector on the bottom of my drivers side airbox is broken and leaks - I could do woth a new one....its the small round collector with the steel gauze in it...

I have tried the usual places but no luck.

Any ideas?

Thanks in advance

[mikesr]

A nice alloy replacement here- but a bit pricey

[Ireland]

mikesr said:

A nice alloy replacement here- but a bit pricey

That's expensive.

Surely it could be made for a lot less than that by a handy local fabricator.

[HarryW]

Ireland said:

mikesr said:

A nice alloy replacement here- but a bit pricey

That's expensive.

Surely it could be made for a lot less than that by a handy local fabricator.

I think I'd be fashioning one out of old bean can myself.........

[longbow]

The standard breather is pants - it allows far too much oil mist to enter the drivers side bank under hard driving conditions. I'd fit a proper breather system, this is how I did it but I don't have aircon to worry about;



You could mount a catch can in the engine bay somewhere quite easily!

[julian64]

Its only fiberglass.

You can buy a bit of resin from the local halfords and paint it on, or if its cracked you can buy a bit of fiberglass ribbon tape from halfords.

If the thing is broken but just not fixed to the bottom of the airbox without leaking, then I suggest drill three holes through the lip and use rivnuts. The thing is then going to stay solidly to the airbox, no leaks, ever.

[peteA]

longbow said:

The standard breather is pants - it allows far too much oil mist to enter the drivers side bank under hard driving conditions. I'd fit a proper breather system, this is how I did it but I don't have aircon to worry about;



You could mount a catch can in the engine bay somewhere quite easily!

Jesus Longbow thats some set up!

I notice you have taken the a breather pipe into each air box rather than the standard set up of the off side only - seems to make more sense...

I would like the alloy item mentioned but not at that price!

Looking at the other comments I think I might be repairing the old one! Fabricating one is an option but fitting the connections for the pipe attachements seems difficult and considering it needs to be air tight to stop leaks....

Dont suppose this is a common fault...?

[The Surveyor]

Pete

Does it have to breath back into the Air Box at all? Would it be feasible to isolate the crankcase breather from the air box and pop one of these on the end:-

http://www.demon-tweeks.co.uk/products/ProductDeta...

Much cheaper

Paul

[julian64]

I'd be carefull about Surveyors suggestion. I'd work fine on any normal car, but youd be amazed how much oil comes up that pipe, and under what pressure.
I reckon that filtre would be clogged to not working in a few minutes .

Do you have that working on your car surveyor?

[brogenville]

Those little breather filters should never be used if at all possible. From "The Car Bible":

Large quantities of water are produced by the normal combustion process and, depending on engine wear, some of it gets into the crank case. If you have a good crank case breathing system it gets removed from there PDQ, but even so, in cold weather a lot of condensation will take place. This is bad enough in itself, since water is not noted for its lubrication qualities in an engine, but even worse, that water dissolves any nitrates formed during the combustion process. If my memory of chemistry serves me right, that leaves you with a mixture of Nitric (HNO3) and Nitrous (HNO2) acid circulating round your engine! So not only do you suffer a high rate of wear at start-up and when the engine is cold, you suffer a high rate of subsequent corrosion during normal running or even when stationary.


The normal breather uses the negative pressure in the plenum to perform crank case scavenging which a breather filter will not.

[longbow]

I did try the 'filter venting to atmosphere' as a first attempt and as Julian says, the quantity of oil mist pushed out of the crankcase was too much for it - it covered the engine bay in oil! I also did quite a bit of research into the AJP design and what I discovered was quite interesting. As the AJP unit is derived from a racing design, it should be expected that the quantity of blow-by gasses should be quite high - this is becasue the engines are designed quite 'loose' to reduce friction in the bores. Added to the fact it is quite a large capacity engine, and you can see how at high rpm and full load, blowby will be significant. Furthermore I do believe that the AJP was originally designed as a dry sump engine - indeed the early Tuscan racer units were all dry sumped. With dry sump engines, a natural vacuum is created in the crankcase due to the scavenging pumps - this assists in clearing the build up of gasses and so the original block would not have required many, if any, breather pipes. I think that when they went over to a wet sump setup, the normal breather system was an afterthought and a usual TVR botch. As far as I can see, it only has the one vent point - on the front cover - and I really think this is inadequate - even my 2.0 16v engine in my MR2 has two - seperate head and a bottom end breather. Some track race engines have multiple breathers.

Another clue I had a lot of crankcase pressure buildup was my dipstick kept on popping out of its seat only after a hard drive. I've since put a small securing chain on it. The engine is very healthy and powerful for a 4.2 so I really don't think there is anything wrong other than the standard breather isn't man enough for a 4.2/4.5 race engine.

[peteA]

The Surveyor said:

Pete

Does it have to breath back into the Air Box at all? Would it be feasible to isolate the crankcase breather from the air box and pop one of these on the end:-

http://www.demon-tweeks.co.uk/products/ProductDeta...

Much cheaper

Paul

Hmmm....was liking your thinking there Paul till i saw the replies! I especially liked the relative cost..!

I'm going to give this a bit of thought...I am currently cleaning caked on engine oil off my engine, chassis, suspension, etc that looks like is has been coming from the breather...there dont seem to be any signs of leaks from elsewhere. Looking at the amount of oil everywhere it looks to have been leaking for some time and backs up the comment about how much comes up the pipe...

Incidentally, the reason for the pipe is to releive the crankcase pressure right...do the vapours have any intended lubrication properties for the engine top end? Otherwise it may as well vent to atomosphere...

If lubrication in the form of oil vapour is part of the breather set up then surely it needs to go the each air box...?

Cheers again guys.

[GreenV8S]

Connecting the crankcase breathers into the air intake with a PCV system is done purely for emissions. It's a bad idea from the engine's point of view since the oil has a very low octane and encourages pinking under load, and also makes any plug fouling problems worse.

Those little filters are designed to filter air going *in* to the crankcase when you have a PCV system. They are completely unsuitable for filtering the breather gases and will block very quickly. For that you need either a catch tank, or a wire separator. The wire separator can also double as an anti-flash device (fire trap) to stop a backfire in the intake from igniting the crank case. Ideally either would be positioned so that they are self emptying back into the crank case when the engine stops.

[peteA]

How about sealing the existing hole up as there are no reasonably priced standard units to put back...form another smaller outlet in the airbox for the breather pipe to connect to...then, in the breather pipe install and inline breather/filter available from, for example, pipercross?

or...

seal the existing breather hole up sealing the air box completely. The breather pipe leaves the engine front cover...install and inline breather/filter available from, for example, pipercross...then run from the outlet to a separate collector mounted nearby on the chassis (presumably this may need emptying every so often..?)

Thoughts anyone....

[longbow]

Yep, tis true that you don't want oil in the intake - it reduces the effective octane of the air/fuel charge and can foul the plugs if excessive. And you are right, the AJP does pull a lot through - into just the drivers side bank with the stock setup. A number of owners have commented that the've had oil pooling in the airbox after trackdays, plus the continual leakage you describe. Another thing is that with the very tight air gaps around the throttles at idle, I found that prior to installing the catch tank, that after a hard blast the engine would sometimes stall when idling. Once I took the drivers side airbox off to find oil all around the throttle butterfiles - this could have been choking the throttles at idle and causing the stalling. It never happens anymore! A simple solution is to buy an aftermarket catch can, stuff it full with stainless steel scourer pads and then fit in inline with the stock setup. This will trap most of the oil and it can be emptied out when full. This is effectively what I've done, although I've balanced the crankcase blowby equally between both banks.

Edited by longbow on Tuesday 23 December 13:19

[julian64]

One final point before you make your decision. Any reselling of the car would cause a person to worry about your car if it had an obvious aftermarket attempt at changing. Unless you were longbow, who has a professional looking system there, most would worry you'd changed the system to hide a problem.

If I was buying longbows car I would know he tracks his car. If I were buying another car with an altered system I'd want to know why, and more importantly satisfy myself the seller was telling the truth. You may not want this sort of hassle when selling?

[GreenV8S]

longbow said:

This is effectively what I've done, although I've balanced the crankcase blowby equally between both banks.

Did you think about putting the breather inlet at the bottom of the catch tank rather than the top? If you're done that it would have been self draining and maintenance free.

[longbow]

I remember thinking about it but decided I didn't want the oil mist from the blowby getting back into the sump since its mixed with combustion contaminants and hence fairly 'dirty'. It would have worked though.

I haven't had to empty the catch can yet once since fitting (over 9 months) but then again I haven't really driven the car much (and Julian I have never tracked my Cerb - yet!!!). I intend on doing some extended high speed autobahn driving shortly though (passing Frankfurt's 3/4 lane autobahns at 4am on Sunday morning) and will be intereted to see if it picks up much oil.

Edited by longbow on Tuesday 23 December 13:50

[peteA]

julian64 said:

One final point before you make your decision. Any reselling of the car would cause a person to worry about your car if it had an obvious aftermarket attempt at changing. Unless you were longbow, who has a professional looking system there, most would worry you'd changed the system to hide a problem.

If I was buying longbows car I would know he tracks his car. If I were buying another car with an altered system I'd want to know why, and more importantly satisfy myself the seller was telling the truth. You may not want this sort of hassle when selling?

I know what you mean but judging by the comments on this page it seems to be an issue with the standard set up...so, any professional modifcation would easily be explained...?

Also, I ve seen many a competition car (mainly dragsters) with this set up...ie. pipe out of crank through a vertical breather/collector (so any oil drains back into crankcase) with the outlet discharging into a 'open to atomosphere' vessel (often a coke can!).

This is an interesting thread - thanks again for the feedback