Oil burning

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Larry
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Oil burning

#1

Post by Larry »

Is it likely that a UL engine would burn oil due to wide, but not excessive, stem to guide clearance?
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Re: Oil burning

#2

Post by RooDog »

I wonder how oil even gets to the valves and guide in a SV Harley engine....
....RooDog...
kitabel
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Re: Oil burning

#3

Post by kitabel »

Loose (more than the .0055" in the manual) intake guides are subjected to engine vacuum and will pull oil in.
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Re: Oil burning

#4

Post by RUBONE »

RooDog wrote: Thu Sep 23, 2021 6:07 pm I wonder how oil even gets to the valves and guide in a SV Harley engine....
....RooDog...
Oil mist and crankcase pressurization pulses. The same way it gets to most engine bushings, tappets, breather bodies, and pistons pins, etc. There is lots of oil mist churning around inside a running engine.
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Re: Oil burning

#5

Post by Larry »

Has anyone experienced a smoking condition in a big flathead directly caused by wide stem to guide clearance?
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Re: Oil burning

#6

Post by Larry »

I guess the problem is either very rare or non-existent.
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Re: Oil burning

#7

Post by kitabel »

Frequently goes unnoticed or undiagnosed.
In general:
Smoke on open throttle (low vacuum + high cylinder pressure) is probably rings (wet compression test raises the CCP).
White smoke on closing the throttle from cruising speed (high vacuum + low cylinder pressure) may be intake guides. The exhausts may also be loose, but only subjected to engine vacuum during overlap, which UL have very little.
Tightening the intake guide clearance down to minimum factory new (.0035") helps, but sometimes it's not the clearance, it's a deep scratch made when a valve with a burr (especially lock groove damage) was dragged through on assembly.
Bronze may be run tighter but how much IDK.
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Re: Oil burning

#8

Post by flat38 »

It has been my experience that worn or oversize guides or worn valves will cause oil burning. Too little clearance can result in valves sticking. I usually fit them toward the larger end of the factory spec. That seems to work best.

I once made my own guides using Ampco 45 bronze and fitted them to the minimum of the spec. They stuck after only 5 miles. The valves had to be pounded out with a drift punch. They were galled so badly that they were unusable. The guides were undamaged and I was able to ream them out to the high end of the spec and with new valves, they ran with no issues for many years.

Flatheads do not have any lack of oil to and above the lifters. If anything, they have too much. Most of them have oil leak issues from the valve covers. My oiling system testing has shown me that even at low RPM there is an incredible amount of oil flying around in the cam chest.
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Re: Oil burning

#9

Post by Larry »

I thank everyone for the input. I'll try to find valves and guides that can be fitted to minimum clearance.
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Re: Oil burning

#10

Post by Andygears »

Knowing nothing about flatheads, might I suggest some of the spray coatings on the valve stems, perhaps ground to a smaller Dia. and flame sprayed, or has this been tried and failed?

Andygears
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Re: Oil burning

#11

Post by kitabel »

I've read of drilling 12 or 15 1/32" holes right through the intake guide body (below the cylinder) and tightening up the clearance to .002". The idea being the guide/stem area still gets oil from mist inside the cover, but the tighter clearance limits how much can get into the intake port.
Anyone seen this?

The crankcase, cam chest, and covers are all experiencing different levels of internal pressure. Their high-low-high cycles overlap, but are never at the same level. This will tend to pump oil mist around. This is what keeps 2-strokes alive in near-desert conditions.
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