Cylinder Head Temperature Gauge Installation

[Wheelman-111]

Greetings:

Last night I installed the eBay CHT that I purchased from a closed BMW bike shop months ago. I thought I'd share my own installation, and hope others will add to it. With better pictures...



1. Select your style and purchase your new CHT. It needs to cover the 200-400 degrees F. range especially.
2. Decide where it should go. Not many choices on Elites unless you wish to mount a bracket someplace. The low positioning of the glovebox invites taking eyes off the road, so don't fixate on it. A glance and then you "read" it in your mind.
3. Mounting. For round gauges mounted where mine is, the tool for the job is a hole saw.

http://search.harborfreight.com/cpisear ... &Submit=Go
These are so cheap I'm surprised they can cut plastic, but no problems. I used my fancy Craftsman set to 2.25".

4. Connections. Once the body is mounted, there is the little matter of hooking it up. Lighting is nice at night, impresses the girls. Well, maybe the nerdy ones... One wire needs switched current. The other can go to ground. It usually doesn't matter which wire for incandescent bulbs, but fancy LEDs will be polarity-sensitive.
The other connnection is to the thermocouple, often a copper ring that replaces your plug washer. The gauge should tell you where they hook up.


That blue thing is a splice connector. You can get one like it at any autoparts store. You just find the wire to which you wish to connect, I just poked around in a connector block using the gauge wire itself. When the light came on, I made sure it went off with the ignition switch, then plugged in. The splicer requires no stripping at all, and doesn't damage the wire to which you connect. Lay the wire in, insert the gauge wire alongside, and snap the cover closed, et voila!

LET THERE BE LIGHT!


And there was light. Also a temp reading as soon as I can route the thermocouple back to the spark plug. Looks like it's about a 6" longer trip than for the Aero...

[toboggan]

Looks nice, i'm going to try to find one from a friend that works on VW's.

[maddog]

thats a good find on that guage, i don't like the spark plug sending unit cuz they break easy so i use an eye loop connection on the exhaust bolt which confirms the same temp, also use header wrap on the exhaust which keeps heat off the engine.

[bakaracer]

thats a good find on that guage, i don't like the spark plug sending unit cuz they break easy so i use an eye loop connection on the exhaust bolt which confirms the same temp, also use header wrap on the exhaust which keeps heat off the engine.

if your hooking it up to the exhaust,how are you getting the correct temp reading for a cht (cylinder head temp) gauge?

[Bear45-70]

thats a good find on that guage, i don't like the spark plug sending unit cuz they break easy so i use an eye loop connection on the exhaust bolt which confirms the same temp, also use header wrap on the exhaust which keeps heat off the engine.

The exhaust will be way hotter than the head temp. The exhaust has next to no cooling by the income fuel and air mixture like the jug and head do. Why not just use a head bolt? Better yet drill and tap an hole in the side of the head and mount it there?

[Wheelman-111]

Greetings:

When I install my bore kit I will follow wise Bear's advice. I need to find a thermocouple in a smaller than 14mm size first. Something just over 6mm to fit under a head bolt with an extra washer?

Anyone coming across a thermocouple source for under %)#@%$40 LMK.

[bakaracer]

for a vdo gauge,good luck!

[Wheelman-111]

Greetings:

I have already found one at Aircraft Spruce to replace the original. I just didn't like the price.

[808BMW]

Grainger has the spark plug sized thermocouple for $21 last I checked, I'd buy 2 and just have a backup (although I'm like that on everything )

[Wheelman-111]

Greetings:

I have a paragraph in my Flash III thread in Scooter Builds outlining my gauge's wonky behavior. The needle is steady most of the time, and above 350 more often than not. (EEEK!)

However it jumps around occasionally and unpredictably, rising to 500+ even just sitting at idle a few times. The old thermocouple used to do that until I replaced it with this one, now it's starting too. I suspect you can only pull the plug/manhandle the sensor ring so often before it starts to fail. That's why I'd like to hook one up more permanently under a head bolt or other convenient attachment point. I may get Grainger's and just sandwich it between a couple of copper washers under a head bolt, but it's be better to find an 8mm and apply it directly to the head below, washer above.

I found this one at Graninger's, unknown if it'll work. Type "J". 0-900 degrees, looks like a ring fitting that's closer to a head bolt than a spark plug... no spec on ring size!

[SpyderMike]

would it be possible to drill a hole in the head, insert a thermal coupler into said hole, then use high temp epoxy to hold it in?

[Wheelman-111]

Greetings:

Certainly the hole-in-the-head idea has merit. Wheelman has several in his own personal head...

Anyway, this is the one I found on Grainger's:

http://www.grainger.com/Grainger/items/5ZY19

As long as I can figure out polarity and Farads-per-Furlong values, it should work. (Mousewheels will be impressed by my knowledge of things ee-leck-tronickal.) Please advise if you know otherwise. The gauge is a VDO. No specs available.

[mousewheels]

would it be possible to drill a hole in the head, insert a thermal coupler into said hole, then use high temp epoxy to hold it in?

Sure should work fine. You can also buy thermocouples that thread in. Inexpensive too (See below eBay item number). Bare thermocouple wire runs over $1/ft where I've been looking, so the threaded termination is a good buy.

I found this one at Graninger's, unknown if it'll work. Type "J". 0-900 degrees, looks like a ring fitting that's closer to a head bolt than a spark plug... no spec on ring size!

Say does VDO say that a Type J thermocouple is used? The Letter code denotes wire alloys used. The alloys have unique properties, one of which is the sensitivity. Some are high output (good for low temp) some good for high temps, corrosive environments. And some are good at being inexpensive Obviously you want the thermocouple wire your meter is calibrated for.

Here's temperature/voltage graphs of some common thermocouple wire

...Farads-per-Furlong values, it should work. (Mousewheels will be impressed by my knowledge of things ee-leck-tronickal.)

When you can get them, Farads-per-Furlong will cost you two wallet fulls, and your favorite thumb.

Themocouple identification. The VDO website offers no technical info as to the thermocouple wire. I searched the 'net' and there's chatter that says VDO uses a 'Type-K' wire. But it is easy to determine by some measurements.

Verification: Place your current ring sensor in boiling water, measure with a DMM. This might challenge the DMM's ability.
Type K 4.509mv at 212F
Type J 5.814mv at 212F

Verification II: Place in a 400F oven (a little easier for the DMM's 1.xxx volt scale to resolve)
Type K 8.3mv at 400F
Type J 11.0mv at 400F

Thread mount Type 'K' thermocouple with a 2 meter lead are available on eBay. Shipping and handling probably lower than industrial and electronics supply houses...
Item 250477077951 10ft type K thermocouple, ($3.99 current / $4.99 ship)
Item 250478557721 2m (6.6ft) type K thermocouple (1.99 no bids/4.00 ship)

--- Screw mount ---
Here's a link to a source for a small diameter (1/4" and smaller) bolt down (lug) style thermocouple. You can order customized lengths. Their reference price is $9 for a 36" wire Type K.
http://www.omega.com/ppt/pptsc.asp?ref=WT

[carp]

That Aircraft Spruce site has a 10mm ring type listed in the Falcon instrument listings.I found more info and better price on that Tempco TRW 00023 on the Drillspot.com site.It's a 1/4" hole,48" lead,going for $19.It is a"J" type.Carp

[SpyderMike]

As long as I can figure out polarity and Farads-per-Furlong values, it should work. (Mousewheels will be impressed by my knowledge of things ee-leck-tronickal.) Please advise if you know otherwise. The gauge is a VDO. No specs available.

http://cgi.ebay.com/ebaymotors/VDO-3109 ... leQ5fParts
this looks the same so you might be able to call them and inquire about the tech specs