7 replies to this topic

[ImagoX]

Sorry in advance if this has already been answered in an old post.

 

I'm attempting to replace the engine in a '91 Mini - the old engine was destroyed in a garage fire and has been replaced with a refurbished crate engine from Seven. I'm in the process of identifying missing parts and engineering solutions.

 

My current challenge: the engine crankcase breather. It was on the old engine, and needs to be replaced. Since I have a later-series Mini with the large brake servo and cylinder assembly, I was going to use THIS HORIZONTAL UNIT as a replacement. I know that some people just put a metal-mesh pod filter on the top of the breather canister, but I've heard the best thing is to plumb a line back up to the intake manifold so vacuum pressure can draw up the fumes and oil vapor for burning. Problem is my new carb manifold (a dual-carb setup - see THIS UNIT) only has a single tapped vacuum port, which I will have to use for the hard line running to the brake servo. I currently have the assembly marked #9 on THIS DIAGRAM in my parts bin which is from the old engine.  

 

QUESTIONS:

 

1. Re: the servo vacuum line: can I replace the current vacuum line with a length of braided hose, which will look nicer? There's something that looks like an in-line filter on the hard line, which I'm not sure if I need to retain or not.

 

2. Re: running a vacuum line to the breather canister: Assuming the answer to #1 is yes, can I place a T-junction in the middle of the replacement line, which I can run to the top of the breather canister, or will doing so lower the vacuum pressure to the servo such that it will interfere with proper operation? My original carb (a single unit which was destroyed in the same fire that claimed my engine) had additional take-offs off the manifold for vacuum-operated accessories, but my new manifold does not.

 

3. If I cannot splice into the vacuum line that operates the brake servo, what are my options? I've seen people who have added a vacuum line for the breather by drilling a hole in the back of one of the carb air filters, but this looks like a hacked-together solution at best. Would such a solution even work?

 

Thanks a million in advance for any advice.  --Matt 

[Stiggytoo]

The filter type thing you have referred to is a 1 way valve

[ImagoX]

The filter type thing you have referred to is a 1 way valve

Oh, I see.. so if I replace the hard line with something else, I should retain it, sounds like. Looks like it's just held into the hard line with a barb-type fitting, yes? Thanks!!

[dow62]

 1234615_1563087360578828_3812211429854398782_n.jpg   91.66K   39 downloadsThe transfer gear casing breather on my engine ( ex Mg Metro) fouled the servo, rather than buy a new one just cut it and re-welded it so it cleared the servo. Piped in to carb using a 8mm T piece (mini bore central heating from hardware store)

[Ethel]

Your problem will be too much vacuum in the line, rather than too little. The single carb connection is shielded by the throttle disc, the twin carb setup had a diaphragm valve to limit the pressure instead. You could use a similar valve and tee in the servo line underneath of (engine side) it.

 

The round thing just in front of the label on the air filter case. The servo connection on the left is on another manifold connection, but could go on the same one as the valve with a tee connector (hose).

 

 

 

You can use braided hose if it's rated for fuel/oil and doesn't collapse under vacuum.

[ImagoX]

Dow - yes, my old setup was a single carb and looked just like your photo. I left the old breather canister on the engine which was melted, so I need to buy a new canister anyway, but good idea on the weld to clear the brake cylinder.

 

Ethel - so, are you saying that even if I don't use a "T" junction in the hose to the brake servo, when I fit a banjo bolt to the port in my new dual-carb manifold I will have TOO MUCH vacuum pressure? I was worried that if I split a line off that it would reduce the pressure and not allow the servo to operate properly; I never thought I'd have a situation where I had too much pressure. If I fit the existing vacuum line directly to the manifold, will I damage the servo? Maybe adding a "T" and using the line to drive both the servo and the breather would actually be a *good* thing?

Edited by ImagoX, 15 September 2014 - 02:46 AM.

[Stiggytoo]

Do your carbs not have breather connections? Unless you fit a positive crankcase ventilation valve I don't think it's a good idea to plumb the breathers directly into the manifold where they would experience full manifold pressure. Instead your next best option would be to route the breather to a small catch tank.

[dklawson]

Servos are supposed to connect to manifold vacuum, not the carb.  It is an issue of "volume" and the amount of vacuum.  More is better. 

 

If you want to run a regular hose instead of a pipe there is any easy work around.  You can source the one-way valve from U.S. vendors like BP Northwest (Google them and search for "check valve" or similar on their web site).  Buy a hose to fit, even heater hose will work.  Now Take a piece of the hose you intend to use to the hardware aisle of the home center.  Look for a long spring like would be used to close a screen door.  Make sure it will fit the inside of the hose.  At home stretch the spring out a bit if necessary to extend the full length of the installed hose.  Slip the spring inside, fit the hose and check valve.  The spring will keep the hose from collapsing under the vacuum.