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I’m assembling a L89. Building this motor up to look factory correct.
obviously aluminum heads and intake have no paint. My question is more about timing chain and oil pan. Would the bolts holding these on be painted orange or would they be bare steel?
ive looked at a couple small blocks and they are painted. I assume big blocks are the same but wanted to check
Im discovering new things on my 79..
my aluminum manifold is in fact painted flat silver...and sloppily..
dont know what your year is but assume most all bolts were painted in those areas
The bolts should be the same color as the item they are retaining. If engine orange is the color of the part immediately under the bolt head, that's the color of the bolt head. If it's a semi-gloss black brace to an accessory, the bolt head should be the same. There could be some bare bolt heads over painted parts, but I can't think of any in the engine compartment. And I do not know what the bolt heads [visible to the viewers] on the outside of aluminum cylinder heads are colored. But, I suspect they were cadmium or zinc plated steel bolts.
If this is a vehicle which you are going to have NCRS judged, you should follow information in their "Judging Guides".
"BLACK" OE Bolts on ALL Vintage GM cars was/is Manganese Phosphate Plated.
This is a non electrical coating process that can be done yourself
if you search on line for the Chemical that is added to heated
water in a stainless steel vessel....
Media blasting the old/original fastener is the biggest challenge whereas applying
new Manganese Phosphate is relatively easy
Preserve the newly coated bolts/nuts with FLUID FILM
The bolts should be the same color as the item they are retaining. If engine orange is the color of the part immediately under the bolt head, that's the color of the bolt head. If it's a semi-gloss black brace to an accessory, the bolt head should be the same. There could be some bare bolt heads over painted parts, but I can't think of any in the engine compartment. And I do not know what the bolt heads [visible to the viewers] on the outside of aluminum cylinder heads are colored. But, I suspect they were cadmium or zinc plated steel bolts.
If this is a vehicle which you are going to have NCRS judged, you should follow information in their "Judging Guides".
Agreed, the NCRS technical information & judging guide is a must if one is interested in replicating factory appearances.
Broadly speaking, whatever was mounted to the block by the engine plant at Flint or Tonawanda got engine paint. What was installed at the body assembly plant in St. Louis was whatever color the parts supplier was required to paint it -- though St. Louis bolts are usually bare steel or black oxide and not painted. There are certainly exceptions which come to mind: the valve cover bolts for painted covers on 454 radio cars. The painted bolts from Tonawanda were replaced with non-painted when the braided plug wires were installed in St. Louis. The aluminum components that were mounted to the block during painting like intake and heads often show over-spray along the adjoining edges with cast iron components.
Best bet for getting it right is by referring to the year-specific NCRS guide.
67:72, There were NO Bare Steel Bolts provided by Vendors......Nor do I think any were Black Oxide
which is inferior to Manganese Phosphate for inhibiting corrosion (aka RUST).......
For those still reading......www.AMKproducts.com is a great source of accurate reproduction fasteners
Bolts I have had replated with MANG PHOPHATE
Last edited by CamarosRus; Aug 6, 2020 at 03:10 PM.
67:72, There were NO Bare Steel Bolts provided by Vendors......Nor do I think any were Black Oxide
which is inferior to Manganese Phosphate for inhibiting corrosion (aka RUST).......
For those still reading......www.AMKproducts.com is a great source of accurate reproduction fasteners
Bolts I have had replated with MANG PHOPHATE
I'll take your word on NO bare steel bolts - I thought the exhaust manifold bolts were bare but see in the '70-'72 TIMJG that they're not (mine were rusted/eroded so much that the head markings were obliterated). As to the black coloration, the guide merely says "black plated" in the descriptions. The definition section indicates either black oxide or black phosphate but no clarification on which may have been used where. If the term "black plating" eliminates black oxide then there you go.
The black plating was the cheapest way to protect the bolts for GM as the suppliers where making millions of them so it was never meant to last 40-50 years. A year or two at best was all it was good for under normal use. The entire engine was assembled when it was painted. The parts not painted where crudely masked off. As Tonawanda was building roughly 250 a hour. That included paint process.
Engine paint- specifically bolts
