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1957 Dommi 88 oil pump

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1957 Dommi 88 oil pump

Posted by john_brookes at August 09. 2018

HELP!!!

I have the oil pump off the timing side. How much force should be needed to turn it over?

I expected to be able to turn it with my fingers. Instead it needs a lot of effort with both hands to get it to move!

It was pumping oil well before I started on replacing chains ect. Is it possible that someone has missed out a shim under the cover or something like that?

I hav'nt stripped it yet, will wait for advice hopefully forthcoming.

John B.

Re: 1957 Dommi 88 oil pump

Posted by philip_hannam at August 09. 2018

Loosen off the 4 screws that hold the body together. But only about one turn for each. Then try rotating the pump gear. If it turns easily retighten the screws a quarter turn each. Then rotate the gear some more turns while doing up the screws a bit at a time. This should help the gears and shafts align into free working positions. Do not over-do the final screw turns.

If the pump is still very hard to turn during any of the above then the problem is either debris inside the pump or some other form of damage.

Re: 1957 Dommi 88 oil pump

Posted by john_brookes at August 09. 2018

Previously philip_hannam wrote:

Loosen off the 4 screws that hold the body together. But only about one turn for each. Then try rotating the pump gear. If it turns easily retighten the screws a quarter turn each. Then rotate the gear some more turns while doing up the screws a bit at a time. This should help the gears and shafts align into free working positions. Do not over-do the final screw turns.

If the pump is still very hard to turn during any of the above then the problem is either debris inside the pump or some other form of damage.

Philip,

I have have done exactly as you suggested and low and behold it is working fine again.

I see a new pump is £200 plus so many thanks.

I have primed it well and no bits have emerged so hopefully all will be well.

John.

Re: 1957 Dommi 88 oil pump

Posted by paul_standeven at November 27. 2018

Should the oil pump be punch-locked or LocTited?

Paul

Re: 1957 Dommi 88 oil pump

Posted by philip_hannam at November 27. 2018

The problem with punch-locking is the mess it makes of the screw threads. Thread locking goo has a draw-back in that it needs to be applied to very clean metal surfaces or it does not work very well. The problem here being that a refurbished pump will need to bed-in and requires some lubricant during this process. I give the pumps that I refurbish a run in oil of up to 20 minutes to help the parts bed-in and to also check the output flow rate. Invaribly after that I have to retighten the body screws a little. I don't dismantle the pump to clean up the screw threads as this may cause the end plates to move and upset the alignment of the drive gear. Generally the condition of the screws decides the need for just tightening or punch-locking.

Re: 1957 Dommi 88 oil pump

Posted by paul_standeven at November 27. 2018

A while ago I lapped the pressure pump because of low feed pressure.  I went for light friction on the pressure side, and reassembled it with engine oil.  On getting the bike running, I had excellent pressure (measured after 40 miles on a hot summer day) 5 lb at idle and 45 lb at a fast idle.

The remaining issue was that it took ages for oil to return to the tank after a week not running the bike.  I concluded that the oil was draining out of the filter on the scavenge side, and the scavenge pump was having to refill this before any oil appeared in the tank.  This meant:

- no rocker or cam oil for fat too long after start-up

- the iron filings from the new bores etc were being liberated into the engine

So I have just lapped the scavenge pump.  It now has light friction.  I'm hoping that the oil filter draining problem will be cured

Is there is a suitable one-way valve I can fit to the scavenge pipe to eliminate this issue completely?

Paul

 

Previously philip_hannam wrote:

The problem with punch-locking is the mess it makes of the screw threads. Thread locking goo has a draw-back in that it needs to be applied to very clean metal surfaces or it does not work very well. The problem here being that a refurbished pump will need to bed-in and requires some lubricant during this process. I give the pumps that I refurbish a run in oil of up to 20 minutes to help the parts bed-in and to also check the output flow rate. Invaribly after that I have to retighten the body screws a little. I don't dismantle the pump to clean up the screw threads as this may cause the end plates to move and upset the alignment of the drive gear. Generally the condition of the screws decides the need for just tightening or punch-locking.

Re: 1957 Dommi 88 oil pump

Posted by philip_hannam at November 28. 2018

On my 650, the position of the oil filter and run of the return line to it helps to keep the filter full after the engine stops. So only the pump and a short length of the return line go dry after lengthy non-use of the bike. On restarting the engine I usually get a return flow inside the tank after around 10 seconds. But I do have a 6 speed worm & drive on my pump.

You could fit a non-return valve in the return oil line to help keep it full but I suspect that your problems lie inside the oil pump and have not been solved by lapping the end plates. These oil pumps will act like sieves if there are score marks inside the chambers or the gear teeth are badly worn. Also the condition of the drive gear end plate is oftern overlooked by the DIY mechanic. Any serious wear in this bearing and much of any scavenged oil will be pushed out past the spindle rather than back to oil tank. More so if there is an oil filter in the return line acting as a resistance to any flow.

Last summer, I checked out a Commando oil pump that the owner had serviced but still appeared to allow wet-sumping after less than a week on non-use. The chambers, drive shaft and end plates were all good but the drive side set of gears had a ridculous amount of backlash clearance. These were replaced by a new set and the problem solved.

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