Don Terrill’s Speed-Talk

I'm not familiar with the SHP oiling configuration, but I'd expect simple passages up from the mains. It's unlikely but possible that some tolerance build-up is allowing the occasional 'failure to connect'.

Also, how are the #4 bearing feed holes clocked? I've seen a chart somewhere that I recall showed 'best' to be 1:00 -3:00 and worst 5:00 to 7:00...

Update: Found it: https://www.google.ca/search?q=%27clock ... XKxD3tlgmM:

(double post)

I have to remember that, if not stated, it's a chebby.

I think its an oil starvation problem and here's why.. Pressure and velocity are inversely proportional, since it is at journal number four at the junction where the galley that feeds this part of the engine joins the main galley the velocity is the highest of all five and therefore the pressure is the lowest. Oil then flows down toward the main and along that path it passes tangential to the cam bearing again giving the oil a lot of velocity past the hole and again low pressure. The cam bearing might mean that you are just using too much clearance/creating too much flow elsewhere in the engine and this is starving the number four bearing under some conditions.

Could be...

Dave,
If the oil is passing an open passage [ ie there is no oil in it ], isn't that going to reduce oil pressure until that empty passage is filled with oil? There is no pressure until there is restriction to flow. So wouldn't an empty space that is causing less restriction result in pressure drop; & oil to flow into the passage in question?

Geoff2 wrote: ↑Sat Oct 14, 2017 5:01 am Dave,
If the oil is passing an open passage [ ie there is no oil in it ], isn't that going to reduce oil pressure until that empty passage is filled with oil? There is no pressure until there is restriction to flow. So wouldn't an empty space that is causing less restriction result in pressure drop; & oil to flow into the passage in question?

I think what's happening is that the oil velocity through the galley's is too high due to loose clearance or something else down stream. The oil leaves the number 5 main bearing area/pump and heads forward using the main galley through the block. The velocity in this galley is the highest toward the rear and the pressure is the highest toward the front. Number 4 being close to the rear sees the lowest pressure going past it. On that type of block the cam bearing is fed from the galley that goes down to the number 4 main. The same thing that's happening in the main is also happening in that side galley, velocity therefore is highest where it is passing by the cam bearing so if it is going to starve anything that'll get it first, not the main or the rods fed by the branch going down to number 4 main. The pressure at the cam bearing's oil hole is simply too low to feed that bearing an adequate amount of oil.

I have seen a few cam bearing failures lately and they have all been Durabond

Can we ask what the main bearing and rod bearing clearances measure on these engines?

ou812 wrote: ↑Sat Oct 14, 2017 10:37 pm Can we ask what the main bearing and rod bearing clearances measure on these engines?

Excellent question.

.0022-.0026
These were stock blocks and bearings were chp-8 mostly

Have you tried running the dart bearing with 3 oil holes??

MELWAY wrote: ↑Sun Oct 15, 2017 9:24 pm Have you tried running the dart bearing with 3 oil holes??

These are what we use...so far no problems that I'm aware of....

Are you running some kind of oddball oil? Or are your customers sticking to something more mainstream?

I ran into a similar issue and switched to Calico coated ACL race cam bearings, No problems now.

The oil was hot enough it melted the cam bearing material.

The melting point of Babbitt is over 400°F. Other bearing compositions such as copper, lead and aluminum are much more; over 1,000° for the latter...