8ba camshaft bearings

[51 MERC-CT]

Anyone know what the acceptable cam journal to bearing clearance limits are? (or what would be the max.)

[GOSFAST]

The industry (Federal-Mogul) recommendation is between .0008" and .0044", this is their numbers. We like to send them out however based more on the same numbers recommended for the rod brg clearances if possible, between .001" and .003". This is more acceptable in our opinion.

We don't necessarily agree with their sizes and we would not settle for the .004" area! We don't really want over .003" in the end.

If possible the clearances on the tighter side will be reflected somewhat in the oil pressure reading, it may show up lower with over .004" on the cam brgs.

In this specific area of all the builds we turn out now we use cam brgs which are "Teflon" coated. This tightens up the clearance a bit. It helps but it is not a cure for holes that are simply too big. These brgs will close it up about a .0005", but the brg's "wear" is greatly extended overall!

You need to pay attention also to the cam journal sizing, we've found some larger than others, here on the high-limit actually helps with the build. Last Isky cam here came in at 1.797". On that build we got .0025" clearance. This proved to be excellent but sometimes "you can't always get what you want" so to speak!

All these measurements should be gotten with a good set of "mikes" and an accurate bore-gauge like a Sunnen!

(Add) Added photo shows cam bores being measured for accurate size and then recorded on ticket!

Thanks, Gary in N.Y.

P.S. Most blocks we measure (and record) come in on the "high", 1.929", this is actually .0005" over the factory limit of 1.9285". The low is 1.9275", don't recall seeing one at that number though!

[Ross F-1]

Five thousandths... see below, for 8RT but can't believe there'd be a difference.

[Ol' Ron]

In the early days we didn't pay much attention to cam bearing clearance. We just stuck in a set of new bearings and said "Good enough". This came to a hault in the mid 90's when I found a "loose" cam. It actually had some play after I installed it. The cam was a .010" under on the cam bearing surface and wasn't marked. There were also some engines with low pressure at idle. After that I began checking, and as Gary said the tighter the better. One builder installed 10 under bearings and align bored for .025 clearance. All this gets expensive, but getting good blocks is also getting harder.

[51 MERC-CT]

Some great info here. My reason for asking is that I have what was said to be (and looks like) a NOS Merc. cam that the journals measure 1.7953" and a block with new installed cam bearings at 1.7993". Giving me .004" clearance.
Considering only a minimal effect on oil pressure I will probably just use (as OL'RON said) the "good enough" approach as it's only a stock build and will most likely outlast me.

[Ross F-1]

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Originally Posted by Ol' Ron

...One builder installed 10 under bearings and align bored for .025 clearance. All this gets expensive, but getting good blocks is also getting harder.

I think you mean .0025" clearance?