Topic: 750 oil pump kit

[bwaller]

I bought a rebuild kit for a 750 oil pump from VintageCB750, but is likely the same kit most others sell as well. The o-rings, shaft seal and gasket are perfect, and the stopper valve spring may be fine. However I wouldn't recommend using the relief valve spring. I have access to a spring tester and tested both the original relief valve spring and the replacement. The replacement is half a wind longer.

Just before coil bind the original spring reads 30lbs, the replacement only 20. The spring must compress approximately 16.45mm before the valve opens enough to bleed off any pressure. The original spring coil binds at 15.88mm, the kit spring at 17.21.

So the kit spring won't allow the relief valve to ever open. I used the original springs. HiPo guys talk about shimming the relief spring. I wonder how often the same thing happens with too thick a shim? I ended up using a 0.5mm shim to stiffen the original spring which still allows the valve to open enough.

Maybe people don't need to worry much about this valve.

[BenelliSEI]

Thanks for providing all the interesting details. The last time I used one of their pump kits, I left the original spring in the pump and tossed the kit spring out. It just seemed a poor sub. Seems I was correct! Good data.

[PeWe]

The result will be too high oil pressure?
If yes, good idea to install an oil pressure gauge.

I have used the forum member Elan's kits.
I noticed not much difference when squeeze with fingers. I do not recall if I replaced  springs or used the old springs.

I have to check. I have new springs from those kits and old.

[newday777]

The result will be too high oil pressure?
If yes, good idea to install an oil pressure gauge.

I have used the forum member Elan's kits.
I noticed not much difference when squeeze with fingers. I do not recall if I replaced  springs or used the old springs.

I have to check. I have new springs from those kits and old.

Per
I've tried to find where the information on Elan's kit but haven't found it.

[willbird]

I just ordered a kit from AllCycleSupply. When I get it I can measure the spring wire dia and coil count. Thinking we could compare that data to stock spring measurements ??

[PeWe]

I looked into my garage where I have a CB750 oil pump kit from Elan's eBay shop a few years ago.

The spring is 37.4mm long as an old stock.
Feel equal between thumb and index finger.

[newday777]

I looked into my garage where I have a CB750 oil pump kit from Elan's eBay shop a few years ago.

The spring is 37.4mm long as an old stock.
Feel equal between thumb and index finger.

Does Elan still have these? I just did an internet search and found them not available.....

[bwaller]

Yes that kit spring has at least 1/2 an extra coil, so likely coil binds before the relief valve opens. Down the page a bit. Maybe find them cheaper too.

https://www.vintagecb750.com/products/4/engine/74/oil-filters-drain-plugs-oil-pump-gauges

[PeWe]

If that valve never opens the pressure should be too high, right?
I have not seen very high numbers.
As many others on this forum when comparing oil pressure.

I have heard about mistakes about mounting valve with huge pressure causing leaks.

This is a very important and interesting subject.
That valve with spring can be checked at a service.

Good to remove pan now and then to look for debris, clean the pump mesh filter from varius stuff that can block the mesh.
Some oils can turn into sludge too.

The Vital kits were available 5 years ago or so.
They also had the rubber plug that sit in lower engine case under the bearing holder for transmission shaft. End of oil channel.
That plug can fly away when cleaning a block outside with a pressure washer.
I have done that twice, I saw where landed so OK. But ordered one with pump kit after first escape attempt.

[willbird]

I got the kit , the spring measures 1.480" / 37.6mm. I count 8-9 complete coils, .063" /1.6mm spring wire dia. Spring OD is .604" / 15.34mm

[HondaMan]

In my 'running' experience, I've found engines with jammed-shut relief valves showing about 70-74 PSI oil pressure (cold, never tested one hot) with 20w50 oil and have heard of 80 PSI once in a while. This normally happened on the K1 and earlier versions when the pump base casting warped a little bit and jammed the relief valve shut, and I didn't see any of them myself until well into the 1990s - they can also jam open in this situation, resulting in very low oil pressure below 4000 RPM.

The too-high oil pressure causes extra flow that shows up across the front of the valve cover's gasket as wetness (with correspondingly low oil tank levels and extra-deep crankcase levels, making other weeps), weeps around the valve-adjuster caps from too much spray, and in one roadrace engine, 'washout points' in the plain bearings of the crankshaft around their oil ports. This looks like a tiny funnel was cut into the oil holes where the flow enters the bearing. I was told (but never have seen) that if left alone to have this much pressure it would eventually 'wash out' the plain bearings, whatever that means?

[Don R]

 This reminded me of the time I tried to unscrew the relief valve cap, and the cap and end of the relief valve came off in my hand.  Thank goodness that pump didn't make it into my rebuild.
  Now I'm wondering what caused that, someone shimming it too much and binding it all up?

 I bought two of those kits, have not used one yet.

[MauiK3]

The relief valve is for a clogged oil filter I think?
If the pressure goes too high and the filter gets clogged due to lack of maintenance would the extra pressure damage the filter and hence the rest of the engine due to filter debris?

[Tracksnblades1]

The relief valve is for a clogged oil filter I think?
If the pressure goes too high and the filter gets clogged due to lack of maintenance would the extra pressure damage the filter and hence the rest of the engine due to filter debris?

I think your thinking along the right track. The oil filter bolt has the clogged filter bypass in it.
The Honda oil pump relief valve is a must. It’s a  gear type positive displacement pump. Like all positive displacement pumps the oil pressure has to be relieved (relief valve) if the pump’ s output exceeds the amount of oil the bearings and other clearances can pass.  The pressure build up would be catastrophic without one..

A stuck relief valve on a cold small block Chevy will tilt the spin on oil filter relieving the pressure sparing the distributor drive’s roll pin and/or the splitting of the oil pump’s cases. A 327 with a cartridge oil filter and can WILL split the oil pump or shear the distributor drive roll pin off before the can fails..

[PeWe]

This reminded me of the time I tried to unscrew the relief valve cap, and the cap and end of the relief valve came off in my hand.  Thank goodness that pump didn't make it into my rebuild.
  Now I'm wondering what caused that, someone shimming it too much and binding it all up?

 I bought two of those kits, have not used one yet.

Could have been overtightened. Very thin material and big nut someone could have mixed with big threaded nuts for high torque.

As the tappet plugs, also possible to crack if tighten too hard.

[willbird]

This reminded me of the time I tried to unscrew the relief valve cap, and the cap and end of the relief valve came off in my hand.  Thank goodness that pump didn't make it into my rebuild.
  Now I'm wondering what caused that, someone shimming it too much and binding it all up?

 I bought two of those kits, have not used one yet.

Could have been overtightened. Very thin material and big nut someone could have mixed with big threaded nuts for high torque.

As the tappet plugs, also possible to crack if tighten too hard.

Where I work we have many 2500 ton hydraulic presses. Each press has 10 micron oil filter canisters. The canisters are sealed with an O ring in a similar way to how the right hand oil gallery plug on a CB750K is sealed. Once metal touches metal the O ring is compressed. Tightening the connection more can never compress the o ring more. Yet people tighten our stuff so tight that you need a 6 foot cheater pipe to loosen them.

[PeWe]

Update about relief valve spring.
Honda stock vs pump kit

I have had thoughts about my CB750 K2 rather high oil pressure when cold, 80PSI, slightly more if rev up to 3000rpm.

The pump has got the rebuild kit. But I was not sure which spring I used.
So I had to check.
- It was a Honda stock spring!

I replaced it with the shiny spring from Vital Motor sport kit.

- Result: 70 PSI at cold start!
60 PSI at 1000 rpm ca 2 minutes later.
Same oil, last test 2 days before replacement.
Oil is new, Spectro 20W-50.  Max 80km ride after last change.

My K6 has that oil pressure too, 70 PSI when cold so I'm rather sure its pump got same spring.

Spring is a max pressure protection like a fuse. So the normal use when warm should not be affected.

I do not know at which pressure the oil filter can be damaged or oil starts to weep.