A CHT sender location option

[grandfatherjim]

"Might as well while the engine is out" install senders for a CHT gauge. I'm putting a sender on each of #1 and #3. Not sure yet whether I'll go for a single gauge with a switch, two gauges, or a dual gauge; I'll worry about that later.
I didn't want to put them under the spark plugs, but I don't want to get into that debate; it's the choice I made after due consideration. This is to show a possible way of mounting the thermocouples in case someone will benefit.

First, I drilled a 1/8" hole as shown:


Then, clipped off the majority of the ring which will not be used:


3/32" hole drilled and tapped to take an M3 bolt, and nearby surface area filed flat to maximize thermal contact.


And sensor mounted, using heat sink compound (the white stuff) underneath. The M3 bolt (stainless in case I want to remove it someday) is 8mm long and 2-3 mm of that is consumed by the tab on the thermocouple, the fender washer, and the lock washer.

[SlowLane]

"Might as well while the engine is out" install senders for a CHT gauge. I'm putting a sender on each of #1 and #3. Not sure yet whether I'll go for a single gauge with a switch, two gauges, or a dual gauge; I'll worry about that later.
I didn't want to put them under the spark plugs, but I don't want to get into that debate; it's the choice I made after due consideration. This is to show a possible way of mounting the thermocouples in case someone will benefit.

Very neat. I debated drilling and tapping when I installed my thermocouples, but didn't trust myself to have enough control over the drill without damaging my brand new heads. I "potted" them in some aluminum-filled epoxy instead. Still holding up.

You might want to strain-relief the cable close to the mounting point to avoid flexion of the wires at the crimp. The metals used for thermocouples tend not to be the most ductile.

When making your gauge/switch choices, consider these points:

• Don't bother with a non-compensated gauge like the VDO, unless you're willing to do mental math to perform the compensation yourself.
  To get the best results, you should run thermocouple hookup wire all the way from your probes to the gauge. Using normal copper hookup wire just introduces more thermocouple junctions and will skew your results.
  If you use a switch, you should use one that is designed for switching the type of thermocouple you are using (ie. K or J). The switch should have contacts made of the same two metals that create the couple. These switches are horribly expensive, more than enough to pay for a second gauge.

[grandfatherjim]

Yes, I have added a strain relief, not shown in the pictures.
I have read up quite a bit on the gauges and am familiar with temperature compensated vs. not, but have yet to decide. I don't want a digital readout so my choices get limited.
These are type J thermocouples, 4 feet long. The Westach gauge I'm favouring comes with a short length of wires with the correct connectors on the ends, and I am told that you can cut that piece and insert regular wire of whatever length you need. Doesn't sound quite right to me.
In any case, I believe I will have my cold end at the 4 foot point.. no? Can we really ignore the connectors just by using thermocouple wire all the way forward to the cab? So I'm thinking of having the connection point high on the firewall, to try and get it away from the engine heat. I don't want to put it indoors as it will introduce a great opportunity to ruin the thermocouples when the engine is dropped in the future.
Jim

[Amskeptic]

"Might as well

Does the sparkplug wrench clear the bolt OK?
Colin

[Amskeptic]

am familiar with temperature compensated vs. not, but have yet to decide.

Let me help you. Compensated.

[grandfatherjim]

"Might as well

Does the sparkplug wrench clear the bolt OK?
Colin

The edge of it rides on top of the head of the bolt.

[grandfatherjim]

am familiar with temperature compensated vs. not, but have yet to decide.

Let me help you. Compensated.

I want to find an analog gauge (works better for my analog brain) that fits in the right hand instrument spot in the dash. I also want good resolution around the 350-400 area. Lots of gauges go up to 700, compressing the area of interest.
Still hunting. I have almost resigned myself to non-compensated with mental math...if pilots can do it...but I'd really rather have compensated alright.
Jim

[satchmo]

am familiar with temperature compensated vs. not, but have yet to decide.

Let me help you. Compensated.

I want to find an analog gauge (works better for my analog brain) that fits in the right hand instrument spot in the dash. I also want good resolution around the 350-400 area. Lots of gauges go up to 700, compressing the area of interest.
Still hunting. I have almost resigned myself to non-compensated with mental math...if pilots can do it...but I'd really rather have compensated alright.
Jim

I got the non-compensated. It comes with a computer behind the steering wheel that can do the math.

Tim

[SlowLane]

I want to find an analog gauge (works better for my analog brain) that fits in the right hand instrument spot in the dash. I also want good resolution around the 350-400 area. Lots of gauges go up to 700, compressing the area of interest.

Analog and digital: best of both worlds. http://www.mglavionics.com/html/velocity_singles.html Look for the 4-channel TC-2, or if you really want to go nuts, the 12-channel TC-3.

[grandfatherjim]

Motor back in and running nicely.
While it was out I painted all the engine tin and the engine bay white, for more light and the easier to spot oil leaks with.
I'm liking it:

[grandfatherjim]

And the CHT leads are tucked up on the firewall waiting for me to eventually install whatever gauge I select: