748 Fuel Pump Mounting Plate

J

Jimmer

Active member
Had the pump assembly out to change filter and check the condition of the hoses. All good, nice easy job and the inside of the tank is squeaky clean however I’ve put it all back together with a new o-ring and I’ve noticed a gap between the mounting plate and the heads of the retaining screws.

Is this correct? O-ring is fully seated as far as I can see and the screws are fully tightened down.

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Jimmer said:
Had the pump assembly out to change filter and check the condition of the hoses. All good, nice easy job and the inside of the tank is squeaky clean however I’ve put it all back together with a new o-ring and I’ve noticed a gap between the mounting plate and the heads of the retaining screws.

Is this correct? O-ring is fully seated as far as I can see and the screws are fully tightened down.

View attachment 60561
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Looks wrong, but can't think why. can you lift the plate against the screw. I did mine a couple of years ago but had no dramas so not much help I'm afraid
 
Cheers guys I’ll have a look next time I’m at it, really strange one, can’t get my head round what’s not right.

O-ring was bought off eBay, seemed like a good fit…
 
I know you probably have, but I'll ask anyhoo, have you compared the the one from ebay with your old O ring?
If its only the ring that has been replaced and there is a problem with fit, I would be checking the O ring dimensions.
 
BobTheBounder said:
I know you probably have, but I'll ask anyhoo, have you compared the the one from ebay with your old O ring?
If its only the ring that has been replaced and there is a problem with fit, I would be checking the O ring dimensions.
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The o-ring fits radially, the flange is fully down on the tank - something wrong with the fixings.

OP: Are all 3 showing the same gap?
 
O-ring has the same cross section as the Ducati one. I’ll check the fasteners today. Really bloody odd!
 
Jimmer said:
O-ring was bought off eBay, seemed like a good fit…
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When it comes to parts where accuracy of dimensions and quality of material is concerned ,
I'm always wary of ebay .

This info might be useful .
It was posted a few years back , by someone reliable / knowledgeable , either here or on another forum ,
but I only kept a note of the link , not where it came from ..... :rolleyes:

Tank flange "O" rings can be as cheap as £1 and from a quality supplier .
But they have a minimum order of £10 , so buy 10 at a time ( they fit many models )

 
There are several different specifications for Viton / FKM and some are specific for fuel. All mine are fuel spec Viton - F.

All Viton seals will be better than Nitrile Rubber but the correct type of Viton should be used.

But that doesn't help this particular issue where the flange is fully down and the fixings heads are gapping.


@Nelly to the 🦇 ☎️
 
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I agree about something looking wrong with the fasteners in the pics , and it makes me think
that the o-ring used has incorrect I/D .

The gap between the flange and the tank surface looks much too small .
It normally takes a fair bit of wrestling just to get it seated , and then some continued pressure
to get the fasteners to pick up the first few threads .

I was also thinking about the material of the o-ring .
The Ducati rings I've bought have always been green , and they feel a bit softer than black viton rings
.... more compressible ?
Or is it just my imagination , and the green colour means nothing ?

..... anyway , just my two Mongos worth ..... :)
 
Duke of Prunes said:
I agree about something looking wrong with the fasteners in the pics , and it makes me think
that the o-ring used has incorrect I/D .

The gap between the flange and the tank surface looks much too small .
It normally takes a fair bit of wrestling just to get it seated , and then some continued pressure
to get the fasteners to pick up the first few threads .

I was also thinking about the material of the o-ring .
The Ducati rings I've bought have always been green , and they feel a bit softer than black viton rings
.... more compressible ?
Or is it just my imagination , and the green colour means nothing ?

..... anyway , just my two Mongos worth ..... :)
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California Cycleworks O-Rings are Red, Black and Brown across the range and are all Viton-F. You can get many colours.

The gap isn't determined by the O-ring.

Edit: Google says this regarding colour: it's a little confusing to read :unsure:


O-rings made of Viton are typically color-coded as black, but new gaskets, seals and O-rings should be green FKM or black FKM, but with a green mark on the outer edge. Usually black, but can be brown, or green as well, depending on the formulation and the item formed from it (sheet stock vs. o-ring).
 
The bolts are shouldered - maybe you have just pushed it in too far and not allowed the bolts to find it's level :unsure:


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My experience has always been that you use the tightening of the three bolts to push the plate into the correct position. If you can just push the plate in fully by hand it's too loose and may well leak?
 
Looks OK to me tbh. If you use conventional screws, some do when the OEM ones are buggered, then all the gaps disappear. Using the shouldered ones, then a gap is normal. The shoulder is thicker than the pump base.
If it doesn't leak, then it's working :)
 
Thanks for all the pointers guys. As I see it the shoulder on the bolts are taller than the material thickness of the mounting plate the plate can never be in contact with the bolt head and the tank flange at the same time, it's a strange design but that's how it seems to me. Leak test when I'm next in the garage but feeling like this should be OK.

@Duke of Prunes, when I fitted it I used long bolts and nuts and washers to pull the plate to the tank and I pulled it up tight. I only fitted the mounting bolts afterwards and noticed this oddity. With everything loose I can't move the plate so thinking that everything is well seated.

@Exige, should have bought one of your O-rings in hindsight to rule out a quality issue, for the life of me I don't know why I didn't!
 
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