Alfa Romeo Forums banner

41 - 60 of 94 Posts

·
Push hard and live
Joined
·
9,336 Posts
Update...

I just test-drove the Fetta after a handful of repairs.

I at first assumed the new sender worked opposite to the gauge. Upon power-up, but before start, it went full span. Oh well, deal with that later.

After driving enough to warm things up, I noticed the gauge was about 7/8 span, and responding to changes in RPM in the correct direction.

So, maybe I just need to drop in a series resistor to set the offset?
 

·
Premium Member
Joined
·
13,690 Posts
So, maybe I just need to drop in a series resistor to set the offset?
You can make it read correctly at just one point by doing that and maybe that is all you need. Someone, maybe roadtrip, suggested a resistor value. The circuit that I posted makes it pretty close over the entire range.
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
If it goes full scale when you turn on the power with the engine off, pretty sure you've got the wrong sender on there. From the OKP website it looks like your car would use the later sender.
 

·
Push hard and live
Joined
·
9,336 Posts
The sender I bought from CA was the one listed for the same-year Spider.

If one ignores digital, most analog instrumentation is just slope and offset. My last company made that kind of stuff, and I taught the class.

I think (hope) I need a new-healthy sender in my 115, so if I can get the correct sender, I’ll just move the one in the 116 over to the Spider.

This assumes that CA correctly sent me to one I ordered, however. Meanwhile, I’ll try the resister, just out of curiosity. About a year ago I bought a variable inline unit sold by a Corvette spares company for use with temp gauges. Easy to use for testing. Almost as easy as black tape.
 

·
Registered
1978 Spider
Joined
·
202 Posts
Discussion Starter #46 (Edited)
I ordered a mechanical gauge and M10 and 1/8NPT tee fitting. I plan to install it on the left side with the oil light sender. Like the old Harley guys who add a small mechanical oil press gauge directly to the engine case.

I did notice that the senders have different size oil holes. The gauge one has a pin hole while the light sender has a much larger orifice. And neither one had a copper washer or any evidence of thread sealant. The light sender did have what appears to be orange Permatec silicone sealant where I would expect a copper washer. These are both threaded M10x1.0 and not 1/8NPT. NPT is tapered and I think will "self seal" to some extent. I don't see how M10 threads can seal without Teflon tape or a washer.
 

Attachments

·
But Mad North-Northwest
Joined
·
10,205 Posts
Yes, tapered threads seal with sealant on the threads, straight threads seal with a metal crush washer (and no sealant.) The gauge sender should definitely have a little crush washer, and if the light sender is definitely M10 then it should too (looks like somebody Mongo'd the install.)

Your call if you want to add a mechanical gauge, but per the discussion above it's really unnecessary if the light works and the gauge at least moves reasonably.
 

·
Push hard and live
Joined
·
9,336 Posts
I have a wide array of resistors, and settled on, I think 460ohms. This has my needle right at the mid mark when making full revs, but it does not settle all the way to zero with power on, but engine not running.

The sender that came off the Fetta says “Veglia” on it, plus some numbers. I’m going to try to find the correct one for the 116, then move the one on the Fetta to the 115 with Jaeger gauges.

CA does not officially support any of the 116 cars, “yet”, according to Tom. I’ll probably get the 116 sender from OKP.

Yes, straight threads use a copper crush washer. Don’t over tighten, or you’ll need a stock of new washers.
 

·
Registered
1978 Spider
Joined
·
202 Posts
Discussion Starter #49
A copper washer is an easy fix. plus adds a little more space to help slide the wrench into place.

A mechanical gauge is cheap, like about $15 including the adapter...and probably way more accurate. I'm also planning to put one on the fuel supply line right before the SPICA pump.
 

·
Premium Member
Joined
·
13,690 Posts
I would be hesitant to route a mechanical fuel gauge into the cabin of the car. I had repeated fuel pressure problems with my GTV6 and I bought a small pressure transducer on ebay and interfaced it to a Spider oil pressure gauge. It read zero when there was no pressure and mid scale at idle and it moved around under load so that I knew everything was working OK. I would not want a cracked fuel line p!ssing on my legs when I am driving.
 

·
Registered
1978 Spider
Joined
·
202 Posts
Discussion Starter #51
both are going under the hood. I have no desire for pressurized oil or fuel to have a direct path inside...
 

·
Registered
1978 Spider
Joined
·
202 Posts
Discussion Starter #52
does my old sending unit even need a copper washer? it's M10 thread but there is a definite "tapper" at the base of the threads. There was no copper washer or any thread sealant when I removed it. All the new ones I see appear to come with a sealing washer but the base of the threads is obscured in the pictures.

This one does not have a complete part number stamped on it...but does have "605" which is the beginning of Alfa spider part numbers and also says "Italy". From the PO notes I've found, this was replaced, but source of this replacement part was not recorded. Is it NOS or a "new" part from AR?
 

Attachments

·
Premium Member
Joined
·
13,690 Posts
It is simple. If it has straight threads it needs a soft washer or gasket. If it has tapered threads it needs teflon tape or a liquid thread sealant - not RTV.
 

·
Push hard and live
Joined
·
9,336 Posts
A “pipe thread” is tapered all the way from the tip to the base of the thread. Superior design tends not to use pipe threads in expensive or critical components, as each removal and replacement slightly erodes the threads, particularly in aluminum. Thus, Alfa uses straight threads with a sealing washer in this application.

Those of us that have played with old Alfas for a while are used to finding poor owner solutions, such as jamming an NPT thread down a straight-thread hole. It’s things like this that have resulted in me having a drawer-full of helicoils.

As with medicine, we should all ascribe to “first, do no harm”.
 

·
Administrator
Joined
·
16,776 Posts
does my old sending unit even need a copper washer? it's M10 thread but there is a definite "tapper" at the base of the threads.
That taper is likely to help center the needed copper washer. And, BTW, I anneal the copper washers - even new ones. Annealing softens the copper so it can conform to slight irregularities in the sealing surfaces. Use ones can be re-used by filing off any burrs then annealing. I anneal even the new ones because I suspect the stamping process tends to harden them. Heat them to dull red (a propane torch works well) then let them cool. A quick polish with extra fine sandpaper laid on a flat surface makes them look good, too.
 

·
Registered
1978 Spider
Joined
·
202 Posts
Discussion Starter #57
I like the idea of dropping the oil pan on a recently purchased used car. Not only will you know if any crank plugs have been pushed out of the crank but you may find an assortment of nuts, washers or master link pieces from the timing chain that previous mechanics have dropped. Also you'll be able to clean up a lot of dirt and gunk that has settled to the bottom of the oil pan. Your oil will look cleaner longer and you can seal the sump with Ultra Grey (and/or a new gasket).
Mark
Sounds like a solid idea considering these engines are known for losing crank pins. So I don't have to buy a lower pan gasket? Just Permatex silicone gasket stuff?
 

·
Registered
1978 Spider
Joined
·
202 Posts
Discussion Starter #58
I anneal the copper washers - even new ones. Annealing softens the copper so it can conform to slight irregularities in the sealing surfaces. Use ones can be re-used by filing off any burrs then annealing. I anneal even the new ones because I suspect the stamping process tends to harden them. Heat them to dull red (a propane torch works well) then let them cool. A quick polish with extra fine sandpaper laid on a flat surface makes them look good, too.
interesting. Never knew about that. I do have some Permatex copper gasket spray I use for other applications. I wonder if a little copper spray when re-using a copper washer would be beneficial?
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
Don't overthink this. Just use a dry washer...it'll be fine. Toughest part is properly tightening up the sender, but even with a stubby wrench and what little torque I can get on there I haven't had it leak.
 

·
Registered
1978 Spider
Joined
·
202 Posts
Discussion Starter #60
well it seems I must correct myself...upon closer inspection of the oil light sender...it appears that it may be threaded 1/8 NPT. Which would explain the silicone sealant that was evident.

I was digging thru my bins of nut bolts washers and had a stash of copper sealing washers. Including 2 new M10 (I think). they fit perfectly over the gauge sending unit and just like ghnl said...that "taper" centered the washer but still allowed the washer to fit flush.

The waring light sending unit the washer would only drop about 1/2 way onto the threads. Those threads are definitely tapered. I got out my digital caliper and they are about .3mm to .5mm of a taper. Not much but enough. SO....is this the wrong sending unit? maybe from an American car? Looking online at senders most seem to picture that sealing washer, which leads me to believe it should be M10 thread.

Obviously they are both close enough to practically be interchangeable...assuming you use Teflon tape or the washer *** appropriate to get a proper seal...Any damage possible from mismatched threads? Or are they close enough to be ok? I would like to put the correct thread type in but can more damage be done by trying to "un-do" it?
 
41 - 60 of 94 Posts
Top