100 or 108hp engine?
 

Hi

According to Volvo's manufacturing records my P1800S was manufactured ("reported OK") 22 Nov 1963 with Engine number 375, chassis number 8683

It would seem that B18B engines from 1961-1963 were 100hp at 5500 and that from 1964-1966 they were 108hp at 5800 rpm.

My Tacho , which sadly doesn't work :( , is a first generation version from observation of the backplate of the instrument however the dial has the markings of the second generation instrument with the red zone starting at 6000rpm however it is different from the second generation pictures I have seen in that the lettering "4 CY Negative earth" is missing. See attached photo's

The tacho looks to me to be made from parts from generation one and two instruments. I'm wondering if my vehicle was manufactured in transition from the 100hp to the 108hp versions.

How can I tell which engine I have?

Your chassis is a 64 model year and should have the 108bhp engine but to be honest after 54 years it wont be making either of those figures and a good 100hp will be better than an average 108bhp engine. In fact a good B18 will be better than an average B20, so its pot luck really.

Your tacho is also correct

Dave;

Up to chassis 10,000, Gen 1 Tachs were fitted, so that's what your car would have had originally, but unless you bought the car new, you can't hope to know what's in there now for certain...and it's a similar situation with the Engine power...that was originally determined by (mostly) Cam, Manifolding, Carburretion, Compression Ratio, and Ign Timing Curve, so who knows what it might be today...if you absolutely must know, some measurements like Camlift and timing, and C-R would have to be performed...

...getting back to the Tach, it's no surprise to me that what's in there now, a mongrel oddity really, doesn't work..it looks like someone made a hybrid of Gen1 internals in a Gen2 Housing as strictly a Dashboard holefiller (and few besides Mark Olson and me would probably immediately notice and recognize this!)...I predict it has only the meter movement, and no internal electronics whatsoever (but this is possibly a benefit, making it a candidate for an electronic conversion! **)...I further expect if you were to remove it from the Dashboard and inspect the rolled edge holding it together, you would see it has been "unrolled" to open and turn into the Frankentach it is now.

See also: http://www.sw-em.com/Smith's%20Tachometer.htm (I guess you already did, because that's where the first two pictures came from...so this is for anyone interested and reading along...)

Good Hunting!

** I might be able to supply contact info of an electronic specialist in Germany who has designed and built a modern electronic drive for a Gen1 Tach for someone there. Contact me directly to discuss. ( I have no financial interest or arrangement with him, but would accept a case of Guiness Stout as a brokerage fee if it worked out...!)

The facia of the tacho's changed to the later style for the 63 model year (chassis 6001-8000) not at chassis 10000, so the facia of Dave's tacho is correct for his chassis no. Some late 63 (so fitted to 64 model year) tacho's with the generation 2 facia still came with the gen 1 backplate and wiring which is why I believe his tacho may well be the correct one. Agreed that if the rear of the chrome bezel is not warped or damaged then it hasn't been pulled apart and that is the best way to tell.

Mike, checked the chrome bezle and it doesn't seem to have been interfered with so I suspect it to be genuine unmolested unit. As I suspected I think this gauge is genuine for the transition model 63-64.

I do however have a problem with it. I finally, yesterday, got around to investigating why it doen't work and found the wiring at the unit disconnected. The (brown) Power wire was showing 5.5v with the ignition on but the engine not running and ranging up to about 10 volts with increasing rpm. However at 5.5v or so with the engine idling at around 800rpm the gauge indicates about 5000 rpm.

Does anyone (Ron?) know what the proper voltage range should be for the unit and whether what I'm experiencing is a fault with the gauge or the remote voltage sensing module?

I'm not that technically minded Dave so can't help re voltage but this was a common problem with P1800 rev counters back in the day I.E. Massively over reading and the usual cure was to fit another gauge which usually worked. The fault is very likely to be within the gauge. Replacements are not 10 a penny like they used to be so if you cant find a good used one I think it needs re-calibrating.

Dave;

It's not as simple as a direct RPM to Voltage correlation...that would make it too easy!...it's an RPM to Current correlation, because it drives a current meter (which I expect has a nonlinear response on top of it...).

...so it sounds like you have a fairly unique gauge...again, if your Tach was the type where gauge was driven by remote module, you have the option of replacing the module with a modernized one...

Mike;

The "generous Tach" is a common age of electrolytic capacitor/calibration potentiometer related symptom, indeed within the gauge electronics.

Cheers