I have finally worked out a measurement from the Draper/Neilsen gauge that I'm happy to stand by and post on here.
When Tony visited we were quickly able to establish that my cambelt is pretty much spot on in terms of tension, according to the Burroughs gauge. As a second double check, Tony had also pre-tested the Burroughs gauge at a trusted Esprit builder's premises before coming over to mine, so we were happy that we have a well tensioned belt as a check for the Neilsen gauge.
The reason for the delay in posting is that I was getting inconsistent readings from the Neilsen gauge at first, and was on the point of suggesting that it's not a good option, and people should steer clear. I've now done a few checks on different days with very consistent results. People with experience of "Gauge R&R" will get my concerns.
Key information for success and to use this advice :
1. Engine to be stone cold - 10-20 degrees C.
2. Engine has run for a few minutes to bed in the cambelt.
3. ALWAYS wind the dial in from the loose position to the required tension setting : i.e. start at approx 25 on the scale and wind it straight in to 16.0, then take the reading. NEVER make small adjustments to the dial and expect a good reading.
The readings on the gauge for a correctly tensioned belt are :
"Tension setting" = 16.0
"Optimum tension" = 14.0
This equates to a side force on the cambelt of 5.5DaN and a deflection of 1.5mm.
See picture
Happily this does relate to the Burroughs. We crudely checked that, and the side load is 10DaN (10 kgf) with a deflection of 4mm.
The span of the legs on the Neilsen is 50mm against a span of 75mm on the Burroughs, hence the deflection should be 2.667mm for a force of 10DaN.
The Neilsen gauge only goes up to 7.9DaN, so a further reduction is required. I applied a simple ratio of 0.75 to both deflection and force.
I first tried 7.5DaN for 2mm deflection, which equates to :
"Tension setting" = 14.0
"Optimum tension" = 13.5
I recommend this as a secondary check only. The gauge is more difficult to read when the dial approaches the same position as the sliding scale.
Picture below
I then applied a ratio of 0.55 to get to a point where the gauge is easier to read. That gave the 5.5DaN and 1.5mm numbers which match with my recommended settings of 16.0/14.0.
Hopefully this is helpful, and may save a few people some money if they can't borrow a Burroughs gauge. My Neilsen gauge cost £16.50 delivered from ebay, so a lot cheaper than alternatives, and a good option if you're not changing cambelts very often.
Happy to be challenged, and/or clarify if I haven't been clear with any of this.
Cheers,
Malcolm.
- Hope you don't mind Stu. Though I say it myself, I think I did a pretty decent job reprofiling it.
