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Author: Subject: How close is too close ?
mcerd1

posted on 13/2/19 at 03:56 PM Reply With Quote
How close is too close ?

(apologies for the giant pics - I've had to go back to photobucket for now and its a PITA)

I'm finally getting round to finishing my engine build - but I've hit yet another little snag

When I first fitted the oil pickup it was basically touching the big end of #2, with a little persuasion (in the form of a 3' lever) I've managed to get this much clearance (maybe just over 2mm) and I'm not sure I want to bend it much further.

the questions is how much clearance should it need ?
I know that 1mm is generally considered safe for a pinto at the top end (piston to head) so I assume the same would be true at the bottom end..... any thoughts ?












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steve m

posted on 13/2/19 at 05:15 PM Reply With Quote
My current crossflow had the same issue when I modified the pick up, to fit a new sump, so I just wacked the pick up tube with a hammer, made a dent in the tube and fitted it, from memory, 3mm gap ?

was fine last year

steve





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coyoteboy

posted on 13/2/19 at 05:31 PM Reply With Quote
Can't envisage bottom of stroke being worse than top of stroke. Top of stroke is the highest load point for the rod/bearing assembly, so highest likely elongation. Crank scrapers seem to have sub-mm clearances? Personally I'd just bend it a bit more though!





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snapper

posted on 13/2/19 at 06:23 PM Reply With Quote
I canít tell exactly from your photo but it looks very similar to my Pinto with Cosworth rods build.
I however was using an RS2000 sump and needed to graft a Cosworth spraybar to the RS2000 pickup, a bit of carfull bending of the pick up bracket pushed the pickup bar a little further away. I did have to get the sump modified to clear the Cosworth spray bar as it hangs under the pickup pipe.
Nothingís simple is it.





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perksy

posted on 13/2/19 at 07:27 PM Reply With Quote
Should be fine but as said a little bit more of a tweek won't hurt
I know you'll already have this covered but its Worth checking the clearance between the actual pick-up head and the bottom of the sump when your happy and assemble it all back together
Especially if its had some 'gentle persuasion'

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ian locostzx9rc2

posted on 13/2/19 at 07:50 PM Reply With Quote
I would try and get 3mm min then it should be fine
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mcerd1

posted on 13/2/19 at 09:29 PM Reply With Quote
I'll see if I can get another mm or so clear then

quote:
Originally posted by coyoteboy
Crank scrapers seem to have sub-mm clearances?

I was thinking that, as I was also fitting one of them too, but they are just an easily bent sheet of metal rather than the pipe that supplies all the oil....

quote:
Originally posted by snapper
I canít tell exactly from your photo but it looks very similar to my Pinto with Cosworth rods build.

That's probably because it's a pinto with cossie rods
But I've used a cossie pickup pipe chopped down to suit my shortened sump

[Edited on 13/2/2019 by mcerd1]





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snapper

posted on 13/2/19 at 09:49 PM Reply With Quote
Iíll add a bit of clarity to the stretch that leads to the piston extending by between 0.75 & 0.9mm depending on revs. This is rod stretch and as such only goes one way, up, because the piston is not physically restrained. Conversely in the down stroke the rod is either in being dragged down or in compression. The bearings donít hit the crank journals because of the thin oil layer so whilst there may be a slight thinning of the oil layer and maybe a slight compression of the big end bearings (I doubt it) my feeling is that the big end bolt heads wonít move anywhere near the amount the piston crown would





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Mr Whippy

posted on 14/2/19 at 12:42 PM Reply With Quote
I think if 3mm could be taken up by your rod moving about then you have bigger issues
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rusty nuts

posted on 14/2/19 at 01:22 PM Reply With Quote
A little tweak with a lever would give more clearance
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Bluemoon

posted on 14/2/19 at 02:39 PM Reply With Quote
quote:
Originally posted by Mr Whippy
I think if 3mm could be taken up by your rod moving about then you have bigger issues


Tend to agree. Snag maybe with CTE effects and vibration will the pickup move???

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snapper

posted on 14/2/19 at 08:53 PM Reply With Quote
There is a lot of negative here, trying to find a problem where there isnít one.
With the pickup bolted firmly to the oil pump and a large bent metal support at the other end, it ainít going to move.
Bending the bracket at the pickup end can be difficult to do right.
Bend it away from the rod bolts and the pickup then angles away from parallel to the sump floor, correcting that causes the pickup pipe to get closer to the rod bolt at another point in the rod bolts arc.
Itís a classic case or one step forwards two back





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Bluemoon

posted on 14/2/19 at 09:01 PM Reply With Quote
quote:
Originally posted by snapper
There is a lot of negative here, trying to find a problem where there isnít one.
With the pickup bolted firmly to the oil pump and a large bent metal support at the other end, it ainít going to move.
Bending the bracket at the pickup end can be difficult to do right.
Bend it away from the rod bolts and the pickup then angles away from parallel to the sump floor, correcting that causes the pickup pipe to get closer to the rod bolt at another point in the rod bolts arc.
Itís a classic case or one step forwards two back


Yep, but if it were me with 2mm clearance I would run it then if worried drop the sump and check for marks...

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flak monkey

posted on 15/2/19 at 06:54 AM Reply With Quote
Assuming the pick up is solid and cant flex at all then the clearance you have will be fine.





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Neville Jones

posted on 16/2/19 at 12:39 AM Reply With Quote
RE the pickup head. Three evenly spaced standoffs welded to the bottom, to ensure clearance to let the oil in is worth doing. Make them 6mm or a bit more.
It has been known on more than one occasion for the pickups to be sucked down onto the sump bottom and end up with oil starvation. Even the stiffest of tubes will bend.

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