Sprocket combination vs speedometer

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Joined: Fri May 20, 2005 7:29 pm
Location: Wasilla, Alaska

Sprocket combination vs speedometer


Post by 51Hog » Fri Jan 25, 2008 8:57 pm

Description: When the speedo indicates 67, the bike is actually moving at 55mph

Post by 51Hog on Apr 4, 2006, 5:07pm

The tooth count on my sprockets are these.
Engine= 23
Clutch= 37
Tranny= 22
Rear= 51
Tire dia.=26"

Right now my speedo is not correct.
When the speedo indicates 67, the bike is actually moving at 55mph.

I would like to correct for this, and using Jack's calculator program-(Thanks Jack)-, I estimate that I will need to change the transmission sprocket to 25 teeth.

I also think that I would like to lower rpm at cruise 65mph to about 2300. What is the Ideal cruise rpm for the FLH? Usually, on other engines, I like to be close to where the engine is putting out it's most torque.

I think my sprocket combination will be the following.
clutch= 37
rear =51

I am looking for someone to double check me.
It is a whole lot less expensive to "Measure twice and cut once"...
What do you guys think?

Post by King on Apr 5, 2006, 12:56pm

Hi 51Hog

Wow! That’s quite a discrepancy and I’m a bit perplexed as the ratios you have now are stock or very close (I believe the stock tranny sprocket has 22 teeth).
The stock sprockets give an over all ratio of 3.73. On my 51FL I ran a 25 tooth engine and 25 tooth tranny for a while and felt it was a bit too “tall” at an over all ratio of 3.02. It was pretty good on the interstate with 65 at about 2500 rpm (on my Tiny Tach) but performance on hilly secondary roads sucked, a lot of gear changing to keep from lugging.
Your proposal with the 24 tooth engine and 25 tooth tranny sprockets will give an overall ratio of 3.15. Currently I am running 23 tooth engine and 25 tooth tranny for an overall ratio of 3.28 which seems a good compromise.
I know we have kicked ratios around a few times in the past but your question regarding optimal RPMs at cruise has not been addressed. My guess is that it should be somewhere between 2400-2800 RPM but I would like to hear from those more knowledgeable than me.


Post by 51Hog on Apr 5, 2006, 4:59pm

Thanks King,
I was wondering if the engine had enough poop with my lard a** on it using the 24/25 combo to climb hills.
You confirmed what I suspected---A little too much gear.
Sounds like I may go with the 23/25.

This should fix the discrepancy with the speedo.
I don't care about the speed needle so much, It is the odometer that I want correct.
Speaking of speedo, any Idea as to the reason the needle will Sometimes swing a 10 mph arc--not necessarily at the same speed, and not all of the time?

Post by panacea on Apr 6, 2006, 2:21am

Hog, sounds like the cable may be a little dry, is it an aftermarket speedo?..MW

Post by 51Hog on Apr 6, 2006, 2:29am

Just finished a 25 mile ride with the 23/25 sprocket combo.
It works GREAT!!!!
Speedo is dead on.
RPMs are down. Plenty of around town go.
Plenty of highway go.
Even being gentle with the fresh build.
Only down side is that now I have to watch the oil light while in fourth. I may end up putting new oil pump gears in her.
Oil light flickers at 45-50mph when hot.
Thanks go out to all on this board for their input------and their patience.

Post by 51Hog on Apr 6, 2006, 2:32am

It is a stock speedo.
Cable was completely cleaned and lubed last year.
I will check it again.
What lube do you recommend?

Post by Jack Hester on Apr 6, 2006, 3:12am

Dale -

A note on the flickering oil light. Did you replace the oil pressure switch with a new aftermarket one? If so, 90% chance that it's setting is too high, as most are. Get a NOS switch, or an old (known good) one, and install. Pressure setting should be somewhere around 7 psi. Some are less. Flow is what you are looking for. Pressure is the first indication. Return to the tank is the guarantee. Your oil pressure may be just fine.


Post by 51Hog on Apr 6, 2006, 3:31am

This is the same oil pressure sender that I was running before the build. I didn't notice the oil light being so insistent before. I will remove the sender, put regulated air to it and with an ohm meter, I will see what pressure she opens/closes at.

Post by 51Hog on Apr 6, 2006, 9:36pm

Very interesting---
I changed the oil today. (Very few shavings on the magnetic oil plug.)
I was running 60 weight Valvoline.
Oil light Off at Slow Idle Engine Cold
Oil light was flickering at 1800 rpm engine hot
Oil light solid on at 1700rpm engine hot
Changed to 20w50 today
Cold engine oil light off.
Hot engine flicker at 1700
Hot engine solid on at 1600

I would have expected the 60 weight oil to produce more oil pressure than the 20w50.
What is the scoop?

Post by panacea on Apr 7, 2006, 1:55am

Hog, like Jack noted,is there plenty of oil returning to the tank? If so I would try another switch,you know what low oil pressure sounds like, tic tic tic..With no audible warning I would think the pressure is ok, if it starts to tic, I would check the Jesus clip on the oil pump drive gear.LOL..Mike

Post by 51Hog on Apr 7, 2006, 4:30am

Yes, there is oil returning to the tank.
How do you define plenty of oil returning?
Solid stream shooting out of the return line 2"? more/less?
There is no ticking, but, I have solid lifters.
I think my warning will be a squueeek......
Almost wish I had hydraulics.

Part of the speedo cable was dry. Oiled it and re- installed. Took the speedo apart, cleaned and oiled that too. There was a lot of garbage built up on the magnet and in the case. It is a wonder it was working at all.

Post by fourthgear on Apr 7, 2006, 8:58pm

The sending unit will only take a Little pressure to open the switch , I used my pneumatic tester to check mine after some one wrote a thread about a new one he bought and it stayed on . I found that mine was stuck , after taking it apart as much as I could , I stuck a plastic straw up into the pressure diaphragm / switch a couple times after cleaning and flushing it inside and got it to work consistently but , went to a pressure gage before I started the motor this year after a total rebuild just to see what pressure I was getting for my knowledge because I had a oil passage welded and just wanted to know . I don't think I would trust it any way , because it was sticking. I believe it would open (light off ) @ about 11/2 to 2 pounds , not sure if that is the way it should be of not but they open pretty low. I now get using 20-50 syn. about 12 pounds @ 55mph , The gage is not going to be exact of course and from motor to motor you are going to get diff. readings but I know its got pressure . As has been said as long as you have good flow coming back to your tank and your tank is warming up with engine you should be OK. Put a gage on and you will see no oil pressure @ idle mine does, but I have good flow and running solids.
And good come back on the motor balancing, my thought too.

Post by 51Hog on Apr 25, 2006, 4:29pm

Well, I found the oil pressure problem last week.
Found it when replacing a blown front head gasket.
Intake rocker block sheared two studs, and slightly bent the other two. No Idea why, as they were torqued with a torque wrench and double checked. Valve and spring clearances were/are within tolerance.--Even with the FLH cam.
Anyway, with the rocker block bouncing in the head, it opened the oil passage up under it and allowed the oil to run into the valve cover unimpeded.
To add to the problem, I found vacuum leaks in the intake nipple threads that had developed since assembly of the rebuilt engine(I pressure checked when assembling). She was heating up too much with these vacuum leaks and thinning the oil too much.

Now while running 20w50, after the engine is at operating temp,
I have to retard the spark to get the oil light to stay on.

(I checked warm compression and I still have 115lbs on both sides.---At least I did not burn the rings and valves out of her.)

Post by fourthgear on Apr 25, 2006, 6:53pm

Man , kinda makes ya wounder what did cause the studs to break! That could have ended up putting the whole motor out for the count. Makes you want to say" glad the head gasket blew" but ya never really want to say its good for anything blow.
Did the bent studs bend toward the intake side of the head or towards the exhaust rocker block or left or right?

Post by 51Hog on Apr 25, 2006, 7:14pm

The studs on the push-rod side are the ones that broke.
When the block lifted on that side, the studs on the valve side levered toward the left side of the bike. Needless to say, I checked for cracks in the head and replaced all four studs. The block was still good. I wondered why the solid lifters needed to be adjusted so soon, and just blamed it on the new build and everything seating in.
Looks like I just got lucky. We will see.

Post by Jack Hester on Apr 25, 2006, 9:30pm

Man, what a fortunate catch. Glad you did find it before major damage.


Post by fourthgear on Apr 26, 2006, 1:34pm

The reason I asked how the studs bent is that I have seen seized rockers that when they bind, the piston will push the valve closed and if the rocker is bound up even slightly it will pop nuts or studs, bend valves etc., all that energy has to go some where. Yours was on the opposite side and if you had a bound up lifter it would have bent the push rod , at least you would think it would . Steel push rods or aluminum ? I know you will be keeping a good eye on it.
Hopefully it was just old weak fatigued metal that couldn't take the strain of the new motor.

Post by 51Hog on Apr 26, 2006, 4:08pm

Aluminum push rods.
Yes, I am watching the valve lash very closely.
I am thinking that someone over torqued them at one time or another.

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