Tacho Adjustments

RobbieW

RobbieW

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Kind of a spin off from the other thread about pulses and such, there are clearly folk here that understand the math better than I....

Just fitted a poly-V belt conversion on my engine, Nanni 4.150, and I'm pretty sure the geometry is now slightly different. The new belt is a 1015, the adjuster sits about 2cm from the end of the travel. The old belt was a 1010 and the adjuster was right out at the end. The conversion comprised replacement pulleys for the water pump and alternator, the crank has a new bolt over pulley so is now larger than the previous.

The tacho has an adjuster, for my engine/alternator (100 amp) combination the book setting for 'Pulse' is 09.41.

I emailed Peachment (ok I'm in Spain and being cheap) on Monday asking the question but havent had a reply.

My feeling is that the tacho is now reading high so any thoughts on verifying/correcting that?

Edit - even though thread is about dead, 20cm was clearly wrong - changed to 2cm!
 
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Most tachos can be adjusted, but my guess would be that yours won't be far enough out to warrant the hassle. Most owners instinctively know the "right" revs for their engine, without looking at a tachometer.
 
It will be reading high if the crank pulley is larger and the alternator pulley smaller - assuming the tacho is alternator driven.

The percentage over-reading is simply the percentage increase in alternator rpm for the same engine rpm compared to the original pulley sizes.

How this translates into the tacho setting I can't say as the figure you quote is meaningless without more info.
 
i have the 4.150HE
my settings for std belt are
011.40

i use 1025A belts


RobbieW said:
Kind of a spin off from the other thread about pulses and such, there are clearly folk here that understand the math better than I....

Just fitted a poly-V belt conversion on my engine, Nanni 4.150, and I'm pretty sure the geometry is now slightly different. The new belt is a 1015, the adjuster sits about 20cm from the end of the travel. The old belt was a 1010 and the adjuster was right out at the end. The conversion comprised replacement pulleys for the water pump and alternator, the crank has a new bolt over pulley so is now larger than the previous.

The tacho has an adjuster, for my engine/alternator (100 amp) combination the book setting for 'Pulse' is 09.41.

I emailed Peachment (ok I'm in Spain and being cheap) on Monday asking the question but havent had a reply.

My feeling is that the tacho is now reading high so any thoughts on verifying/correcting that?
Click to expand...
 
Thanks for the thoughts so far:
I've no idea what that pulse number means, theres no description in the reference books I have, though sailorman's input may help (btw, thats the book setting for a 60 amp alternator)

Just measured the old and new crank/alternator pulley diameters:
Old crank = 112mm
Old Alt = 73mm

New crank = 130mm
New alt = 60mm

So the ratios are quite far apart at 1.53 to 2.16, which suggests a 25% difference?
 
Looks like you'll have to experiment with the settings. Start by getting the idle rpm to be the same as previously but don't worry about absolute accuracy.

That 25% difference will be great for maximising alternator output. I don't think a larger crank pulley is available for a 4.108 otherwise I'd certainly fit one. (already have a 60mm alt pulley)
 
sailorman said:
how much was the conversion pls
Click to expand...

Give or take £350 inc VAT, Peachment say its for the 100A alternator only. I used to get lots of black dust when pushing the alternator hard (720 a/h of domestic to fill). The rationale is to build better resilience into what is the backup charging system, built in generator is primary.
 
In very rough terms, 2500rpm showing on the tacho previously should now show about 1770rpm. So if your tacho has a simple adjustment, you could run the engine at an indicated 2500rpm and then adjust the tacho until it reads 1770rpm.
 
Thanks all - empirical I like!

Only waiting for the replacement raw water pump shaft seal to arrive (discovered dripping on testing the conversion) before trying out :)
 
sailorman said:
i assume you ordered a spare set as well :cool:
Click to expand...

Oh yes, http://simplybearings.co.uk/shop/p7...Oil+Seal+with+Garter+Spring/product_info.html x 2 - it has a stainless spring, though the previous had lasted c. 1000 hrs.

btw, if you go for the conversion - the bolts supplied for the new water pump pulley are about 5mm too long and foul the static casing when screwed home. Also took about the same off the new crank pulley bolts as they slightly protruded out the back of the original crank pulley.
 
after some 10 yrs & 1000hrs i will not be spending £350, i will put up with the dust


RobbieW said:
Oh yes, http://simplybearings.co.uk/shop/p7...Oil+Seal+with+Garter+Spring/product_info.html x 2 - it has a stainless spring, though the previous had lasted c. 1000 hrs.

btw, if you go for the conversion - the bolts supplied for the new water pump pulley are about 5mm too long and foul the static casing when screwed home. Also took about the same off the new crank pulley bolts as they slightly protruded out the back of the original crank pulley.
Click to expand...
 
RobbieW said:
Thanks for the thoughts so far:
I've no idea what that pulse number means, theres no description in the reference books I have, though sailorman's input may help (btw, thats the book setting for a 60 amp alternator)

Just measured the old and new crank/alternator pulley diameters:
Old crank = 112mm
Old Alt = 73mm

New crank = 130mm
New alt = 60mm

So the ratios are quite far apart at 1.53 to 2.16, which suggests a 25% difference?
Click to expand...


According to my arithmetic the alternator will now run at 1.41 times the speed at which it did previously so your tacho will read high by the same proportion

130/112 x 73/60 = 1.41

It will now read 1410rpm when the engine is doing 1000rpm .. (assuming it was correct before the change)
 
Or you could do what I did- buy a Chinese laser tacho on ebay for £8 inc postage to UK, measure the actual revs on the flywheel and adjust the meter to read the same.
 
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