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MG Midget and Sprite Technical - vernia timing and crank ventilation

I am just finishing off a 1275 that has been engine modded head, cam and what looks like a mini spares vernia cam belt setup replacing the duplex chain. This looks to be well sealed from the main sump. So as expected lots of oil out of rear sump seal due to over pressurisation. Where should I fit the vent to the Y into the SU's. Top of the tapper chest cover was my first thought but thats where the air is suposed to go in through the cap.
ian slaney

Is that the plastic version you have? on my old ali one it has a vent.
Brad (Sprite IV 1380)

Noop its like yours its the C-AJJ3328 kit and just found it on their web site. Mine does have a vent, but will that suck through the seals that are added as part of the kit.
The full story was, it was blocked off at the breather and the vac from the carb had also been blocked off, I connected it back together tonight but looking at the kit with seals I convinced myself that this would not work.



ian slaney

Hi Ian where abouts in Humberside are you? I am south of the river.

The 1275 does not have tappet chest covers as were fitted to the B series engines and early small bore A series engines. Thus that is not an option however a large bore breather on the rocker cover (is that what you meant with tappet chest?) would do some good. I am not sure if this would be good enough to stop oil leaking from the rear as that is very difficult at the best of times even with an after market seal kit? But it would be a start.
Robert (Bob) Midget Turbo

Hi Bob
Sorry, yes I meant rocker cover.

I'll give both a go, might be able to measure which if any gets to pull a -ve on the sump. The leak is really bad, i'll have to have another go at it. Dont really want to have the engine out it's just getting to summer.
ian slaney

Ian... Man Im there with you brother... a couple of options

Im just guessing on this 1st canablise the little seperator from an old cover and mount to the new cover
and run the vent tube as normal to the carbs


2 install oil catch tanks.. thats been huge help to me

tie into that same vent tube from the valve cover to the carbs

maybe tap the side of the block at the blob of metal for the fuel pump location and use it as a vent if you can find suction somewhere maybe to a catch tank then to the carbs agian

IMHO the issue is at higher speeds the carbs lose a chunk of vacume and cant suck out the positive air pressure like the carbs can when its running at idel.... thus my quest for a 2 part Evac system... I got a few ideas on the table... will see what happens

I wish you lots of luck

Prop
Prop

<anorak>It's "Vernier."</anorak>

;-)

-:G:-
Gryf Ketcherside

Wierd or what!! I was just reading up on this 2 part evacusump in the good book ( Vizard p351) original transfere case breather and rocker cover both plumbed into an oil/air separator (return to top of sump, but bottle would do) the draw was to a back fire valve fitted to the exhaust, it says the back fire valve must pull at least 18cfm to operate. So maybe this takes over from the PCV valves (x2)which were mounted into the intake manifold.

The dual PCVs into the intake will sort out idle and if I can find a back-fire valve and a separator could do the exhaust. Then I might get a clean drive!!

So it all looks a bit more complicated than I hoped.

Just mounting the original separator to the from of the new ally cover - I still dont see that the SU hose will draw through the seals on the shafts, might be wrong I will try and borrow an air sensor from work to prove/disprove.

Thanks for all your comments.
ian slaney

Vernier - So what!
do you have a contribution to help me solve my problem?
ian slaney

MiniSpares sells an adapter that goes on that unused fuel pump hole that you can mount a breather to.

A common mod for mini folks is to use this adapter and one of the breathers that usually gets bolted to the flywheel cover of a mini to it.

This could replace the breather you lost from your front cover. Or, you can add it for further breathing, above and beyond the other breather.


Norm
Norm Kerr

Thanks Norm
I like the sound of that idea, I hadnt thought of that. Thats what I think i'll go for.
Cheers
Ian
ian slaney

I wasnt going to say anything for awhile, but being that your in a hard way Ian Ill drop one of my secret mods Ive been working on for awhile...all on paper so far, but the therory seams intact and sound

one of the big problems with hooking up the gulp valve to the exhaust pipe that you where reading about from visard is you need to have a free flow exhaust with no back pressure, bends, curves or obstructions (and no a worn out gutted muffler dosnt count it still has back flow enough to trip the gulp valve) I learned that about 2 months ago...basically to do vizards design you need ither early 70s camero chrome side pipes from patroit exhaust or straight pipes with no muffler, yeah your neiabors will love you at 4 am. in order to cure this situation. LOl

The Ansewer... (no not the song from Sarah McLachlan)

what Ive come up with is this....

Get an old 8-10 hp lawn mower 1 inch in-line muffler from back in the 70s stlye and weld it on to the exhauste pipe at a 45 degree then put the gulp valve on the back side of the lawmn mower muffler and ADD a peice of pipe about 1 foot beyound and 1 inch in diameter beyound the gulp valve.... by doing this you avoid any back flow that can close the gulp valve and there is no curves or bends or obstructions that can intrupt the exhauste gas speed of the exhauste flow because the gulp valve is 2nd to last in the line and just a 12 inch peice of pipe 1 inch in diameter to maintian the fast flow of the exhauste thats needed beyound the gulp valve and to create the suction needed to draw out the positive air pressure from the engine. and the exhauste noise is still muffled aka... VIA the inline lawnmower muffler

Will it work?... I cant tell ya for certian... Who knows? Its just something im going to try in a month or so down the road... for what its worth when I was 12 years old I coated my pink boy wonder nuts and worm with poisen Ivy, truly beliveing all the while that doing so would result in the best fun ever for the weekend... that was the same weekend I learned ive only got good ideas about 30% of the time.... If it dosnt work, then id certianly would not try the poisen IVY on the man parts, it wasnt as much fun as id hoped.

I do have a better idea for secoundary suction but its fairly radical, never seen before and purely my own concept so Im hanging on to it for a while... I just hope Bill Young cant be bribed or convinced to spill the beans...LOL

Prop
Prop

to follow up on what norm was refering, you will need an oil catch tank, and you cant vent to atmoshper as you will still have positive crankcase pressure... perhaps use the fuel pump breather location norm ad I mentioned and run a tube from that to the gulp valve om the end of the inline lawn mower muffler I was descibing in the above thread.

with the catch tank and the fuel pump breather hooked to the Lawnmower muffler you wouldnt need to add the orginal oil seperator to the new timing cover.

Prop
Prop

Ian, i have an evacusump system & it helps a lot. I teed into an adapter after the LCB.


Brad (Sprite IV 1380)

Ian
I have the same kit on mine. I have put an extra breather in the rockercover (you can see it on my engine in thread on general), one on the fuel pump hole, and an extra one where the dissy was as I am using megajolt programmable ignition.

I'm hoping these 3 will be enough as I also have a weber and do not want to use inlet vac to draw fumes out.

Matt
Tarquin

I will be moving the vent to the dizzy also when the megajolt is on the new engine.
Brad (Sprite IV 1380)

On every race engine I have ever built (and that's lots now...) I have only required 2 breathers - 1 from the rocker box of decent dimension (say 3/4"-1" hose) and another 1/2" hose from the timing chain cover. These are vented into a oil catch tank which is then ventilated to atmosphere. If you fit the rear main seal correctly, use a 20/50 oil or similar viscosity and run the engine in properly, then you really shouldn't have problems with rear main leakage...

On my latest engine I have installed a Titan vernier belt drive kit - that didn't have a breather, but it did have a tapped hole so I have fitted a 1/2" tapped aluminium breather pipe into it, however if I wanted to fit a breather hose into the block of an engine then the fuel pump hole is the obvious solution - just make sure you fit a bend into the union facing upwards to prevent the oil splashing out from the crank into the pipe...

To be honest it seems to me that if you have to set up an evacusump system as postulated by Vizard you are 1) overcomplicating things or 2) you have too much blowby past your piston rings and haven't deglazed the bores properly/haven't run the rings in sufficiently so the crankcase is overpressuring...

The only reason I can think of to run an evacusump is if there is some sort of construction and use regulation in your country and/or state which prevents you running a catch tank vented to atmosphere...

Regards

JB
James Bilsland

Interesting James,

How are you creating the nessary negitive air pressure in the crank case if your venting to atmosphere after the catch tank... it seems you would have "even" atmospher at best and "Positive" atmospher on high susained revs

Id be curious what pistons you use, what rings and your clearances for both the piston to clyinder and and ring gaps


My guess if you have NEVER had blowby and you have an "Even" to sometimes" Positive" crankcase pressure your engine must be super tight

Are you doing something special to the scrol seal ... recutting the screw function possiable


I just dont see how that posisabe esp on a race engine, a pure stock street engine maybe.

Are you sure you got oil in the sump...LOL
Prop

I agree with James. Our 1380 racer (Omega pistons and rings, race clearances) is vented similarly (albeit I used -8 hose to the rear of the rocker box).

We don't suffer from blowby (never have) and have never had issues with leaks from the rear. Having said that, our rear seal is of the lip type because we have all steel main caps.

And no, the engine isn't 'super tight'. I don't build such beasts. Turning torque at the front pulley (head off) is less than 10 ft.lbs
Deborah Evans

I agree too, but i have evacusump now & i intend to keep it, especially as the next engine is forced induction.
Brad (Sprite IV 1380)

I'll go with James and Deborah, although I haven't built a race engine, my fast road 1420 A series had a 1" bore rocker breather into a catch tank and 1" breather from the fuel pump port, via an oil separator with drain back into the sump, into the catch tank. Apart from the first 50 miles or so when it chucked out oil while the rings were bedding in, by 100 it had settled down to normal levels and didn't leak. I think negative pressure is not required, just minimal pressure to allow the oil drain back from the rear scroll int the sump. 2 x 1" bore hoses provides much increased flow capability compared to the standard breathers so leading to minimal crankcase pressure.
David Billington

well thats certianly part of the puzzle that the none leakers have in commom

1 inch Hoses and PVC valves. and venting the rockercover...1 inch wow that large

Ill certianly make the change from 1/2 and 5/8 inch to one inch inside diameter vent hoses

maybe Ill get lucky and once The rings bed in mine wont leak ither

a fast question ....

on my rocker cover Im using a 3/8th inch inline PVC valve set up horisontially, on the side of the rocker cover. When I upgrade to 1 inch, should I enlarge the hole to one inch and install a 90 degree elbow and have the New 1 inch PVC valve installed on top of the 90 degree elbow so the PVC valve is now Vertical instead of horizontial... or will that have no effect, just increase the size of the vent hose and the PVC size

Sorry I have to disagree... negitive vs positive crankcase is so important, I got the experiance on my side

Prop...25 miles on the clock so far, Hoping Ill be leak free at 100 also.

Prop
Prop

Prop,

I would say from my experience that if you only have 25 miles on the engine then don't bother reporting back about blow by until until you've done a few more miles on the engine, like 100 or more, and it has had a chance of bedding the rings in properly. I noted recently that you mentioned wanting to replace gaskets due to blow by, at such a limited mileage it's to be expected, so just get on and use the engine.


Plenty of advice has been given by othera also, try and take advantage of it.
David Billington

Shish David Not so loud, yeah i got a bit more of a deeper issue beyound basic ring break in, but we dont need to tell the others...LOL

I just got caught up in this converstaion. hopefully i can work out the hairy little bugs this weekend.

Prop
Prop

Sorry been away for a week just back,
ground off the oil separator from the old timing cover welded to a new plate (yes with a hole in it) fitted to the old mech fule pump location, and hey presto back seal not leaking !! Very happy, thanks fellas. Job sorted.
Ian
ian slaney

This thread was discussed between 05/05/2010 and 16/05/2010

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