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murray.arnold
murray forbes-arnold
croatia
(16 posts)

Registered:
09/13/2018 01:25AM

Main British Car:
1973 MGB GT ROVER 3.5 V8

MGB V8 breather plan
Posted by: murray.arnold
Date: September 13, 2018 03:48AM

Good day.
I have a ROVER 3.5 POWERED MGB. I work overseas and had to put the car into a local garage to remove the SU carbs and install a Holley 4 barrel. The guy also installed new cast rocker covers which are not vented. No holes anywhere apart from the oil cap. II had issues and had to force the guy to return my car. So now I have a number of issues that someone can maybe assist with. I have to now work out the breathing system and what parts and where to run everything. I have looked on google images and have seen similar conversions and also rocker covers with different breather pipes and small filters etc. In addition to that there is also a pipe coming from the carb of which I have no idea its use. Maybe someone can assist me with what I need and where to install it. Thanks.

IMG-20180630-WA0014.jpg
20180829_170802.jpg
20180829_174616.jpg


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5657 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: MGB V8 breather plan
Posted by: BlownMGB-V8
Date: September 13, 2018 03:16PM

You do need to figure out where those hoses go. Try pulling on them and checking for what else moves. Or maybe blowing air into them.

On your PCV plumbing, assuming you'd rather not modify your valve covers I can think of one way to do it.

But first, a 4bbl carb is calibrated for a large suction line used to draw vapors from one valve cover while fresh air is drawn in from the other. That fresh air comes from the air cleaner so that at full throttle the blowby that is overwhelming the system goes down the carb throats and keeps the engine bay clean. A PCV valve is added to the line from the carb to regulate the vacuum leak so that the idle mixture can be accurately adjusted. That is what you are trying to duplicate. The vacuum line should usually be about 3/8" and the fresh air line either 5/8 or 3/4" depending on how much blowby the engine is expected to produce. So first, buy a PCV valve for the 215 or 3.5 Rover engine fitted with a 4bbl carb. Maybe something from another sports car line that used that engine, or an American sedan. If that won't work for you shoot for an engine of similar size, probably of American manufacture. I'd go larger rather than smaller.

You need access to the crankcase in two places. You have one if you fit your oil cap with a riser which you can drill and tap. Those were used on lots of Rover engines and should be easy to obtain. The other place is the mechanical fuel pump block-off plate, assuming your engine's front cover was made to accept a mechanical pump. That plate can also be drilled and tapped. You will have to decide what size fittings go where based on the size of your lines, but typically the large fresh air line will go to the fuel pump plate. Avoid kinks.

VERY IMPORTANT! To avoid the possibility of your lifter valley cover being blown out by an internal explosion (and I've had that happen) be sure that there is a flame trap of some sort in the large fresh air line. This can take the form of a bronze or stainless pot scrubber pad if nothing else.

Jim


murray.arnold
murray forbes-arnold
croatia
(16 posts)

Registered:
09/13/2018 01:25AM

Main British Car:
1973 MGB GT ROVER 3.5 V8

Re: MGB V8 breather plan
Posted by: murray.arnold
Date: September 13, 2018 11:32PM

Jim, here is the photo of the carb
the carb.jpg


joe_padavano
Joseph Padavano
Northern Virginia
(117 posts)

Registered:
02/15/2010 03:49PM

Main British Car:
1962 F-85 Deluxe wagon 215 Olds

Re: MGB V8 breather plan
Posted by: joe_padavano
Date: September 14, 2018 10:35AM

The blanked out areas on the valve covers are supposed to be drilled for the breather and PCV valve grommets. This is very common. Don't sweat it. The large hose on the side of the carb is where the PCV valve is supposed to connect to. Frankly, find a shop that has a clue about this. Clearly your current shop does not.


MGBV8
Carl Floyd
Kingsport, TN
(3509 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: MGB V8 breather plan
Posted by: MGBV8
Date: September 14, 2018 11:29AM

Quote:
Frankly, find a shop that has a clue about this. Clearly your current shop does not.

Clearly. They installed the carb backwards. Not that it won't run fine that way. It just looks so wrong.

Then again, maybe that is SOP for a RHD car...... still looks funny.



Edited 1 time(s). Last edit at 09/14/2018 11:40AM by MGBV8.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5657 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: MGB V8 breather plan
Posted by: BlownMGB-V8
Date: September 14, 2018 01:14PM

I believe you are correct with your questions, and note that Rover did use a large screw-in flame trap (painted steel cylinder) which uses the same thread as the oil fill plug and has a 3/4" hose barb at the top. (A pretty good indicator of the diameter of hose required) Most aftermarket round chrome air cleaners come with a plastic or pot metal elbow that fits a punch-out in the bottom cover so there's your simplest fresh air vent if you are willing to machine the rockers. Hopefully your guys didn't throw the elbow away. You or your machine shop will need the large drill and tap. Ebay is a good source for those sorts of things, or if you had found a particularly good deal on the rocker covers it may be cheaper to just buy the spare set and sell the left overs.

If you use a screw-in pcv valve, perhaps with a 90 degree top fitting it makes the other side even simpler. Note, the smaller diameter boss cast into the valve cover is offset from the large one. It also may be a bit small for a 1/4" NPT thread, you'll just have to look at it. But I think it can be made to work.

As Carl said, spin the carb around and the cables look much nicer. It'll work either way of course so your decision.

You still need to sort out where those extra hoses go. If one of them was dribbling oil you might want to make that a priority.

Jim


murray.arnold
murray forbes-arnold
croatia
(16 posts)

Registered:
09/13/2018 01:25AM

Main British Car:
1973 MGB GT ROVER 3.5 V8

Re: MGB V8 breather plan
Posted by: murray.arnold
Date: September 14, 2018 11:24PM

Thanks guys. As for anyone in Croatia with v8 knowledge. Well that's just not going to happen. I noticed that the carb was on the other way after looking at photos. I will have a look at the cables for the choke and the throttle and see what is best. Its now got a manual choke and also there is no kick down mechanism from the gearbox. Something else for me to look at.

So I think I now have a plan in my head. But need advise on what is the best throttle linkage to buy for the carb. The current one is home made and unreliable. I am not home until Christmas so I have time to make a list and order up everything.

Many thanks guys for all the help. I will get this beautiful car of mine running properly one of these days.



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5657 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: MGB V8 breather plan
Posted by: BlownMGB-V8
Date: September 15, 2018 11:36AM

Yeah, the carb needs to be oriented correctly for the kickdown to work since otherwise it won't even hook up. Carb linkage is typically just a simple cable with a bracket to hold the cable sheath. The choke cable may need a return spring if it is the OEM style braided cable, a solid wire will not.

Jim


88v8
Ivor Duarte
Gloucestershire UK
(609 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: MGB V8 breather plan
Posted by: 88v8
Date: September 16, 2018 02:04PM

Don't run the car with no kickdown. It will burn the gearbox, quicktime.

Kickdown bracket, here [rimmerbros.com].
Real Steel used to sell them, might be worth a call. [www.realsteel.co.uk]
I used this one with a BW66, no reason why it won't work with whatever box you have.

I have an Edelbrock 1404 on my Rover V8. No PCV. I sort of emulated the original SU breather setup, connecting from the front of one of the factory rocker covers to the bottom of the air filter. The other rocker cover has an air inlet with a filter. The inlet is at the back, so it draws air diagonally across the engine.

Despite not having any pcv, it doesn't pull oil. But the engine is quite fresh so there is little blowby.

Ivor


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5657 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: MGB V8 breather plan
Posted by: BlownMGB-V8
Date: September 16, 2018 11:09PM

I agree on the need for the kickdown linkage.

The 4bbl carb is not calibrated for the UK type PCV plumbing unless it was specified for a car with that system. Since these are uncommon in Europe I assumed you were referring to a US spec 4bbl. You can use it that way but you may have to re-calibrate the carb not just at idle but at all throttle openings and under all loads. It is much easier to fit the US spec PCV system.

An open breather on the valve cover is 50's tech. It will create an oil film on everything nearby over time, and put hydrocarbons in the air that would be otherwise burned. But, your choice.

Jim


murray.arnold
murray forbes-arnold
croatia
(16 posts)

Registered:
09/13/2018 01:25AM

Main British Car:
1973 MGB GT ROVER 3.5 V8

Re: MGB V8 breather plan
Posted by: murray.arnold
Date: September 17, 2018 06:32AM

I will do the proper cycling of gases back through the carb. I don't want to be sucking in to the cabin hydrocarbons. I will burn them off and let the car behind breath it in. I am in touch with holley and will arrange a full new carb linkage set up with kick down linkage, Also new kick down cable for a BW35 box, which at the moment is purely on an educated guess.

Thanks guys. I am now getting my head round this system. Much appreciated.


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