Oil Pump Shim Advice

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Pasocb
Posts: 86
Joined: Wed Aug 09, 2017 11:14 am
Location: Paso Robles CA

Oil Pump Shim Advice

Post by Pasocb »

Anyone have experience shimming a low mileage oil pump chain? All the references that I have found simply say to Shim the pump down until the chain slightly deflects under light pressure applied by thumb and forefinger (or something similar). These references don’t differentiate if a new or used chain is being adjusted. I did read that run in chains should be set looser but not how to set them. Anyone know where I can find some good information on this or have firsthand experience?
1981 635 Hennarot
1980 635 Polaris (Project)
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Brucey
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Re: Oil Pump Shim Advice

Post by Brucey »

if you measure the chain pitch carefully you can work out where the worn chain will sit on the sprocket and therefore how much slack to allow it to have. If you overtighten a worn chain it will wear at an absurd rate, because the rollers will have to slide up and down tooth faces when they are loaded, and the loading will be one tooth at a time.

Essentially you need to allow enough slack so that the chain wrap (round the sprockets only) is allowed to be longer than nominal by the %-age chain elongation.

For example if you have a 10mm pitch chain that is worn by 0.1%, you need to allow 0.01mm extra chain length per tooth of wrap. Thus if it is wrapped round 30 teeth an extra 0.3mm of chain slack is required. To achieve this shim the chain until it is tight and then remove no more than 0.15mm of shim. If the chain won't pull tight round the full wrap of each sprocket, you get some slack for free, and you can remove a smaller amount of shim than suggested by the calculations.

To measure the chain stretch, put the inside jaws of a set of digital verniers between two adjacent rollers and zero the calipers. Then measure ten more links worth. If the chain is nominally 10mm pitch then the measurement should be 100mm and if it is worn by 0.1% then the measurement will be 100.1mm. This measurement ignores roller wear and only measures pin bushing wear, i.e. it measures the true pitch of a worn chain.

hth

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Pasocb
Posts: 86
Joined: Wed Aug 09, 2017 11:14 am
Location: Paso Robles CA

Re: Oil Pump Shim Advice

Post by Pasocb »

Brucey, I appreciate your extensive explanation of what is going on with a worn chain under load and how to go about setting it’s lash. Having a better understanding of what is going on should help me as I move forward. Things are a little more complicated than just sitting lash on a slightly run in chain and sprocket set for me however. The engine freshen up includes a new timing chain with both sprockets including the dual crank sprocket. This means my oil pump drive will have one new sprocket in the mix.
This week I ordered some additional shims and a new oil pump chain to cover my bases, but wasn’t able to source a new oil pump gear to make it easy. I will say my existing gear looks to have very little wear though.
Thanks again for your input.
cb
1981 635 Hennarot
1980 635 Polaris (Project)
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Brucey
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Re: Oil Pump Shim Advice

Post by Brucey »

FWIW chains run with tension at speed anyway because of inertial loadings but if a new chain is run on slightly worn sprockets, you get higher chain loads than normal at low speeds too. The reason for this is that the wear from a worn chain leaves the wells between teeth virtually untouched, but wears the flank of each tooth at the new PCD of the worn chain. This leaves a small ramp between the unworn well and the new flank wear position. This causes the chain to seat imperfectly and move when loaded.

You can see this happening if you exert a torque through a new chain/worn sprocket arrangement; the chain seems to 'ride up' all the teeth at once in a way that doesn't happen with a new chain/new sprocket. I don't think this is particularly harmful in an oil pump drive but it may cause more wear than normal until the chain and sprocket settle into one another.

Suggestion; if possible, turn the used sprocket the other way round on its mountings, so that the drive is against the unworn flanks of the teeth.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Pasocb
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Joined: Wed Aug 09, 2017 11:14 am
Location: Paso Robles CA

Re: Oil Pump Shim Advice

Post by Pasocb »

I like your advice to flip the used oil pump gear esesentially giving me fresh wear surfaces to work with. With the new chain along with the fresh crank sprocket and flipped oil pump gear, I should be able to Shim the pump as shown in the shop manual.
Thanks,
cb
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