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OP: Oil Pump Single or Twin Start Oil Pump


Rob H

Well Known and Active Website User
VOC Member
Starting to look at the restoration of the early B rapide and engine upgrades required.

On the ol pump which would need looking at can some one explain the pros and cons and differences between a twin and single start?
 

vibrac

Well Known and Active Website User
VOC Member
I have had twin start pump but I think its a false trail and not worth the candle
All my racers for the last 10 years have had single start without any lubrication problems*
In my opinion Bananamans auxillary Honda pump is a much better option for extended component life

*In a way not comparable as of course I use Castrol R
 

Bill Thomas

Well Known and Active Website User
VOC Member
I would not use a twin start again, It doesn't need it, At high rev's it comes back to the tank too fast,
And on a standard "C" Twin it squirts oil out the breather hole in the filler cap,
I think the Twin start wears out quicker, And a lot are fitted wrongly.
You can fit a deflector just inside the Oil Tank.
To me just not worth the trouble, I did use them for a few years.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Bill, you are certainly correct in that they don't last as long as single start p/p's but the first couple I had didn't have the gear with a helix, Clev Trev showed me a mod he does where he grinds to the root of the gear so the worm does not come into contact with the run off when the gear is cut. Now they have an angled cut gear so better alignment for the double start. Mine have always reached beyond the 100k but the apexes of the gear & worm are razor-sharp.
bananaman
 

timetraveller

Well Known and Active Website User
VOC Member
Trouble with this question Marcus is that you will get lots of opposing views. Mine is that the twin start pump is well worth the hassle of fitting and the problem of oil coming out of the filler cap is just not there if one fits a curved deflector to aim the returning oil flow downwards, rather than towards the opposite side of the filler neck. I used a bit of a can (baked bean or similar) and held it in place with the screw which is supposed to limit the oil flow to the rear chain. It cost nothing and took a few minutes to make and install. The problem is/was that several years ago someone made a twin start worm without inclining the teeth on the oil plunger... The other problem was that someone also made the teeth in the plunger with too large a radius cutter and thus the run out of the gears was too shallow and caused very early wear on both components. ClevTrev's mod is a really nice idea. I have never found a down side to having the oil going round faster.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I used mine with the proper angled plunger, This was in the 70s,
Some people say there was no such thing, But I have proved it and put photos on here !.
If you drive steady every thing will last longer, But I was always after top performance,
On the road and Sprinting and Road Racing, All with the same Bike.
 

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