Bedford 28HP Manifold Heat Riser Flap

[44GPW]

Hi all,

 

I need a bit of education and guidence please.

 

I've just fitted a very good used exhaust manifold to my MW. It had a complete working heat riser flap. The biothermal (think thats what it's called) spring had come off but i re-attached it.

 

I warmed up the engine and all seemed ok, except i didnt notice that that flap had moved position? I expected it to (from closed to open) assuming it's start point was closed?

 

Anyway, the engine idled and reved well and seemed to splutter a bit when i moved the flap position by hand.

 

My questions are.

 

1. I know the flaps purpose is to divert hot exhaust gases to the intake manifold to heat up the engine quicker? Does this happen with the flap OPEN or CLOSED? Whats the flaps starting position? I assume closed?

 

2. If the spring is not functioning correctly (weak) i assume the flap will remain in it's starting position? What would be the outcome of this as far as the engine running is concerned?

 

3. Was it normal to experence the engine running rougher when i moved the flap by hand when the engine was warm?

 

Hope all that makes sense?

 

Thanks in advance

 

Richard

[Pete Ashby]

Hi all,

 

I need a bit of education and guidence please.

 

I've just fitted a very good used exhaust manifold to my MW. It had a complete working heat riser flap. The biothermal (think thats what it's called) spring had come off but i re-attached it.

 

I warmed up the engine and all seemed ok, except i didnt notice that that flap had moved position? I expected it to (from closed to open) assuming it's start point was closed?

 

Anyway, the engine idled and reved well and seemed to splutter a bit when i moved the flap position by hand.

 

My questions are.

 

1. I know the flaps purpose is to divert hot exhaust gases to the intake manifold to heat up the engine quicker? Does this happen with the flap OPEN or CLOSED? Whats the flaps starting position? I assume closed? Yes closed ie hot gases to pass around intake manifold

2. If the spring is not functioning correctly (weak) i assume the flap will remain in it's starting position? What would be the outcome of this as far as the engine running is concerned? possibly increased fuel consumption and poor re-starting with a hot engine(Vaporization of the fuel in the throttle body and inlet manifold giving an over rich mixture)

 

3. Was it normal to experence the engine running rougher when i moved the flap by hand when the engine was warm? I would be surprised if you could detect the difference just by moving the flap on tick over, on the road under heavy load you may experience some loss of power

 

Hope all that makes sense?

 

Thanks in advance

 

Richard

 

See replies in blue you can get new bimetal springs from most of the jeep spares providers

 

Pete

[44GPW]

Thanks for that Pete.

 

Just to further my understanding, does the spring contract or grow as i warms?

 

Thanks

 

Richard

[Pete Ashby]

Thanks for that Pete.

 

Just to further my understanding, does the spring contract or grow as i warms?

 

Thanks

 

Richard

 

 

The spring will try to get longer (expand) the outer end is fixed on a stop so the expansion happens at the inner end of the spiral as this is fixed to the spindle it therefore turns the spindle that opens or shuts the baffle. One thought occurs, you have got the outer end of the spring on a stop ? if not it won't be able to turn the baffle.

 

That Master of the spanners Richard F will be able to give you chapter and verse on the vagaries of the Bedford 28hp it would be worth seeing what he thinks. I'm sure he'll be along soon when he sees your title.

 

Pete

[44GPW]

Yes, the spring is attached to the baffle spindle and the stop on the cover as I repositioned it.

 

How long does it take before the baffle should start to open?

[Richard Farrant]

That Master of the spanners Richard F will be able to give you chapter and verse on the vagaries of the Bedford 28hp it would be worth seeing what he thinks. I'm sure he'll be along soon when he sees your title.

 

 

 

Thanks Pete!

 

When I overhaul a manifold on the bench, a quick check to see the bi-metal spring is working is to play a blowlamp towards it, you will quickly see it move. A visual check from the outside, providing the spring is fitted correctly is to look at the balance weight on the flap spindle, it should be away from the engine when cold and towards the engine when hot.

 

regards, Richard

[44GPW]

Hi Richard,

 

It's facing away (flat of counter weight parallel to engine) when cold. How long should it take before the spring is hot enough to move it?

 

Thanks

 

Richard

[Pete Ashby]

Thanks Pete!

 

regards, Richard

 

Your welcome Mr Farrant....... credit where credits due

 

Pete

[Pete Ashby]

Hi Richard,

 

It's facing away (flat of counter weight parallel to engine) when cold. How long should it take before the spring is hot enough to move it?

 

Thanks

 

Richard

 

The opening time will be dependent on a couple of parameters

 

1 the ambient temperature......if it's cold outside then obviously everything takes longer to heat up

 

2 the amount of work the engine is doing.... for example on a cold day at tick over the exhaust manifold may never get hot enough to open the baffle fully. If however it's a hot day and you start up and run at fast tick over for 5 to 10 minutes it would not be unreasonable to expect the baffle to be near fully open.

The short answer is the baffle should be near fully open after a couple of miles at road speeds on a average ambient temperature day

 

Pete

[44GPW]

Thats great Pete, thanks.

 

The fact i've only really tested it on tick over then is not a true result of whether or not the spring is working. Once i've renewed the oil lines to the filter i can road test, then as you suggested, i can replace the spring with a Jeep part if needed.

 

Thanks again.

 

Richard

[Pete Ashby]

Thats great Pete, thanks.

 

i can replace the spring with a Jeep part if needed.

 

Thanks again.

 

Richard

 

Your welcome Richard, jeep, or CMP, both will do the job

 

Pete