Test of repro burner bell and burner plate for no 96 type stoves

Received a package from UK today and I could not wait to try these repro parts on my 1939 Primus 96.

Comparing burner bells :
Repro is 36 gr and outside diam (OD) at the top is 45 mm. Slots for burner plate is 6,5 mm deep
Orignal primus is 44 gr and OD is 52 mm. Slots are 3,5 mm deep.
Height was the same. But repro did not have this rim at the top the lower tube. This rim stops the vaporiser entering into the bell. Vaporiser tube protruded app 3 mm higher than the original.
Together with deeper slots for burner plate this was a bad combination.

Comparing burner plate:
Repro is heavier than original and the shape make it sit lower in the slots. If you use it upside down it will be 1 mm higher. Weight is 37 gr
Original is 26 gr. And sits higher in the slots.
I did not try to swap burner plates during the test. Both will fit the other burner bell.

Also repro do not have this rim below the slots. Because of this and the smaller diameter I could not fit my BD cap.

Due to the heavy burner plate I gave the repro parts an extra preheat that is 3 times. But to no avail as the photos shows. When lifting the burner plate with some pliers, flame pattern became much better and the colour turned blue.

Next step will be to cut new shallower slots in burner bell and turn burner plate upside down, Or try an original burner plate.
Last two photos shows repro before and after increasing burner plate height.Repro parts are on left side in photos.

Bjørn

 

@boknasild
Thanks thats good to know
Cheers

 

I wonder how these compare to BD 3D printed burner plates.

 

@snwcmpr
Yes Ken I wonder myself.
If you want to make a repro part why not use a NOS part. Make a mould of it or print it on a 3D printer or whatever.
Get it so close to the orignal as possible so you don't have to do these adaptions to make them work.

 

@boknasild
Just to confirm, the first flame shot is the original burner bell and burner plate?

Disappointing performance from the repro pair.

John

 

@presscall
Hello John
Yes that is correct. I need to learn how to insert text between photos.

Bjørn

 

It looks to me that there is not enough room between the burnerplate and the rim of the bell on the repro pair. It looks very tight.

Wonder if it would help to trim the edges of the burnerplate to create more space?

 

@janders

You are correct in that the space is narrower. I found the burner plates to be a close match although the new burner bell is a smaller diameter. The flame plate notches are also notched wider & deeper causing the flame plate to sit lower into the burner bell versus the original that sits slightly above the top of the burner bell.

 

Unlikely the original 96 silent damper will fit either.

 

Interesting. This is a good test.

The shape of the repro bell looks more like the later U-shape Optimus type bell (not the latest 71 type). Those later ones lack the rim and a silencer will just roll around in it. However, the slots for the plate is completely off, so did not get those right. The one here have even deeper slots than the one on the ebay listing.

There is no rim on top of the repro bell tube, to hang on top of the lipstick. Will the repro get stuck on the lipstick?

Again – very interesting, thanks a lot.

All the best, e

 

Hei Bjørn,

Does the BD cap not fit at all into the repro burner bell, or does is only sit loosely? I am using the BD silent cap (3 D printed version) in my Optimus 96 (late model, with narrower burner bell than your original one). It sits high there, but works.

Takk og hilsen, Philipp

 

@janders Yes I will take the Dremel and remove metal from the burner plate first. Will try this weekend.
@Pillepalle3 My BD cap will not fit at all.

 

Unfortunately the depth of the slots did not remain constant during the production of Optimus 96s. They became shallower as the years progressed. I did not notice this change in Hjorth and Bahco made Primus 96s however that does not mean that the same did not apply

I have never compared burner plates but it is possible that these also varied in depth depending on their age

The reproduction is a copy of an early Optimus burner head

Regards Bryan

 

The distance between the jet and the plate need to be right on a lipstick burner. There is an interval where things are OK, but too long or too short – as boknasild demonstrates – and you have trouble. Whoever designed this repro did not get this right.

The stove makers back in the day may have changed this slightly as the designs changed, but they of course got the distances right.

The earlier Optimus bells have the rim and will take a silencer, no problem. Later the rim disappeared – like on the repro, and a silencer will not fit.


Bugger – I might have to get one of these repros just too play with.

All the best, e

 

An update of this repro saga.
Tonight I did not remove any metal just fitted the burner plate on top of the bell. Also tried the original plate on the repro bell.
When the original plate was fitted in the slots it burned better than the repro. I consider this due to it is thinner and sits app 1,5 mm higher.
It seems to me that distance between top of lipstick and bottom of plate is critical.
Flame looks good when plate is laying on top of the bell. To make new shallower slots I do not think will help.
So next step will be to try to insert a kind of washer/distance ring inside the tube of the bell so lipstick will sit lower. A 12 mm washer is just to big.
More work for the Dremel tool.

Bjørn



Repro on top of bell.





Repro on top of bell with bottoms up.





Original inside slot. Yellow flames. Some soot.





Original on top of bell.

 

@boknasild

Sorry to highjack your post

I received my package today, I tried the burner bell and plate with a Burmos 96, Primus 96 and a Monitor 17B all with the same results as boknasild, I tried the original and new flame spreaders in various combinations still with the same results. The burner bell was a sloppy fit on all the different lipsticks.

IMO the repro bell and cast plate would look nice on a shelf queen, but not suitable for use without some major surgery.

Regards Richard

 

@richmay you've just confirmed what I was thinking. The sloppy fit of the bell is causing the burner head to sit too low. I've never measured them but some of the 96 type lipsticks I've used over the years appeared to be fatter than others.
If the bell sits too low on the lipstick the result is the same as if the flame spreader sits too low on the bell. The result is incomplete combustion. Something to do with the way that air and fuel mix inside the burner head. @kerophile had a fancy technical term for it a few years ago.
As an experiment you could try one or two wraps of aluminium foil around the top of the lipstick. I don't know how hot the stem of the bell will be when it's running so don't let it burn for too long.
If it works you will need to find a more permanent way to shim the gap between the bell and the lipstick.

Regards
John

 

Hi @Jeopardy here is the link:

https://classiccampstoves.com/threads/primus-no-96-yellow-flames.17755/#post-181340

Best Regards,
Kerophile.

 

Is anyone feeding this back to the seller so they can make improvements?

 

@richmay So yours was in the same condition as mine. I think I will do some surgery to the burner plate.
Remove some metal so the diameter get smaller and make more room between the plate and rim of the bell.
Any thoughts on that gentlemen ? Will it help ?
@Spiritburner I have not contacted the seller yet. Will very soon.

Bjørn