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MG Midget and Sprite Technical - Titan Manifold / PCV

After spending a long time trawling through the Archives, I can't find an answer, so am hoping someone out there can provide one please.

My engine has been rebuilt and has only just been run again. I am having an oil leak problem from the rear scroll area when the engine is running, and believe it is the usual crankcase pressure situation. I had the breathers from the block side cover and the timing cover going through the single HIF38 (on 1098 10CC motor).

I think I need to tap the inlet manifold so as to be able to fit the PCV and run the breather pipes through that, which I hope will keep oil loss to an acceptable level?

As it is a single carb inlet manifold, does the tap need to be central on the manifold ? On the Titan, it would be easier to put the hole into one of the two flat areas on either side, but I don't know if this would give an unbalanced vacuum effect ?

I apologise if the above lacks technical knowhow in trying to explain it ! I am very much an amateur mechanic whose past experience with A series has been with Mini Cooper and S. This is my first midget.

Thanks.
M W Sutherland

Mine is an HIF44. Does your HIF38 have the same pipe connections as my HIF44 in this picture? See the read arrow marked "crankcase breather"

If so, then you don't need the full vacuum from the manifold.

All you need do, is remove the PCV valve from the connection, and connect the breather hose directly to the side of the HIF.


Lawrence Slater

I wouldn't have thought it matters whether the take-off is central or to one side. There is the potential for a lot of suction there anyway (probably too much!).

I hope you appreciate (if you don't you soon will!) that this is Lawrence's all-time favourite subject for which his research has been considered for a Nobel Prize. It was only his reputation for using stilsons to remove rear axle nuts which caused his downfall.
Graeme W

I think Lawrence has several aliases and is covertly starting engine sucking oil type threads throughout the BBS :)
Jeremy Tickle

Thanks for replies so far guys.

Lawrence - what you suggest is the set-up I have at present. The HIF38 is exactly the same as the 44 except for the bore size.
M W Sutherland

MW, l have the same arrangement as Lawrence shows, but on a Titan manifold. If the vacuum is connected to the carb you don't need a PCV valve. But you do need a controlled air input of some sort to the system. Usually achieved on a 1275 with the correctly vented oil filler cap and an otherwise sealed system.

Your use of 2 take-off points makes it something of a hybrid but it should still work if you try a vented cap. If this still doesn't work l would try sealing off the rocker cover breather and its corresponding hose to the carb and see if that simplifies the fume movement
Guy W

This is a slight side issue, so apologies. Lawrence, in your photo you appear to have machine screws attaching the air filter backplate to the HIF. Do you happen to know what the threads are for these. I tried 5/8ths and M8 and both seemed very tight - I don't want to strip the carb threads.
Nick
J.N. Williams

I assume you mean 5/16 rather than 5/8.
I can't say for certain, but I would imagine they were either 5/16UNC or 1/4whit.
Dave O'Neill 2

Into alloy, I am pretty sure I used 5/16 UNC.
Guy W

Thanks Dave and Guy. Yes, my mistake - 5/16th UNF. I'll get some UNC's.
Nick
J.N. Williams

Yup, I think 5/16 unc as Guy and Dave said.

And as Guy confirmed MW, you don't need the mushroom valve, but you do need to vent the rocker cover, to allow air to be drawn down through the engine.

Don't feed the rocker vent to the air filter or any source of suction, or the system will be pulling against itself. As Guy said, all you need is the vented oil filler cap.


Nope, not me in alias form. And whilst I still have my stilsons, I now use my home made hub nut socket. So can I get that prize now? LOL.



Lawrence Slater

OMG! Can I ask a basic question?

The oil is forced out of the scroll at the end of the crankshaft because of pressure which bypasses the rings and pressurises the sump. The gasses have to escape somewhere so some will get out the t/c breather and the rest through the scroll, causing the leak.
There is a need to help the gasses on their way by applying suction from the induction side of the engine hence connection to the manifold via pcv or to the carb.
If the rocker cover can breathe to let air IN, why doesn't that reduce the effectiveness of the suction.

Pretty fundamental question and I'm sure it is covered in that original thread but with 2500 pages it's a lot to troll through. Suspect it is something to do with the oil building up in the timing cover.
Graeme W

You are more or less right, Graeme. But the system has 2 functions. One is to extract the harmful and corrosive fumes that build up in the crankcase and for this it needs to be able to draw in clean air via the filler cap ventilation. But the amount and ease with which this is done is fairly critically balanced, so you need the correctly vented filler cap.

The second function is to lower the crankcase pressure created by piston movement and blow by. The aim here is to limit the tendency for oil to be forced "against" the direction that the rear scroll is supposed to be creating.

So the 2 functions to some extent work against each other and need to be quite finely balanced. Too much air flow entering the system and it won't create the required negative pressure. Too little, and it won't clear engine fumes.
Guy W

Thanks to all once again.

I think I might have a non-vented oil filler cap !!

Will acquire a vented one and otherwise stick with the breathers through the carb, and see if that improves things.
M W Sutherland

The seems to be some confusion here as MW didn't mention venting the rocker cover to the carb. He said the timing case. This also is confusing as the 10CC engine doesn't have a vent pipe from the timing case, (unless a later tc has been fitted) only one from the tappet chest. If MW has fitted an extra breather by fitting a later tc, and the correct vented oil filler cap is present, and the breather from the tappet chest is being used, I would think it would help the engine breathe better.

My 10CC engine vents from the tappet chest via the standard separator to the breather port on he HIF44 with no problems.

Another thing that springs to mind is that the engine has been rebuilt. Has the "moustache" been disturbed? If it has not been correctly refitted, no amount of breathers will stop oil getting past the scroll.
Bernie Higginson

Sorry. By tc I meant timing case. I didn't notice that tappet chest has the same initial letters. Doh! But I think you get my drift.
Bernie Higginson

MW a quick test to see if your cap is vented or not.

Place a polythene freezer bag over your oil cap and a length of string or cable tie loosely arount the filler neck Then start the engine and pull the cable tie/string tight around the neck of the baggie and watch.

Does the bag get sucked flat? If yes - it's vented.

Hope this helps. I did this on Sunday to a GT6 and it worked.
Greybeard

THanks for that Guy.

But how do you stop the oil getting sucked up into the carb.................

I'm off!
Graeme W

"But how do you stop the oil getting sucked up into the carb................."

Drain all the oil from the engine. ;).
Lawrence Slater

I knew all that testing would finally get to the right answer Lawrence
Graeme W

;).
Lawrence Slater

With the temporary thread drift to home-made rear hub sockets, I had intended fabricating something similar for the 'B', as it has a rather awkward octagonal nut!

In the end I gave up and had my Midget socket modified to fit the aforementioned nut.

As well as milling away four of the points, I also had the face machined flat, as the original chamfer considerably reduced the contact area with the very thin nut.

Hopefully, it will still work on Midget hub nuts, too.


Dave O'Neill 2

I love a bit of duality from time to time. :).
Lawrence Slater

Lawrence,
In the image of your HIF44, I see that you have cut and angled the spacer to reduce the carb height. Was this a problem in terms of alignment of the bolts, and how much did you leave at the bottom? Any other problems with this? I could do with a bit more clearance with my new set up.

regards,
Nick
J.N. Williams

Hi Nick,

I was a long time ago that I sliced it, but I don't recall any problems at the time, and haven't had any since.

It's not thick enough to cause any bolt angle problems, but I do remember opening up the central hole to chamfer the small resultant lip off, -- probably top, and or bottom, but it will be obvious when you've cut it.

Here's a close up. I believe I left the full thickness at the top and halved it at the bottom. I made the cut on the manifold side of the spacer.


Lawrence Slater

PS. Looking at that, I appear to have 2 gaskets on the manifold side of the spacer. Perhaps I had some unevenness, and used an additional gasket for a better seal. I honestly can't remember though, as I cut it about 15 years ago. But it certainly worked fine for 14 years until I reverted to twins early this year, or late last year when doing engine breather/oil sucking experiments.
Lawrence Slater

Lawrence,
Thanks a lot for your speedy reply - will try that out.
best regards,
Nick
J.N. Williams

This thread was discussed between 14/09/2015 and 26/09/2015

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