Technical Engine bay finish - paint or underseal?

[paul in manche]

With the engine out and in pieces I decided to sort out the inside of the engine bay, but I'm trying to work out how it was originally finished. I've started scraping off the 'stuff' on the panels, and so far I've found 3 different paint colours, and probably 2 or more coats of some sort of underseal The one nearest the surface is really quite rough and looks as if its been applied with the sort of machine used to pebbledash houses, it also appears designed to retain as much muck as possible. Farther down there seems to be some sort of smoother finish, possibly bitumen based which either comes off in flakes or has gone quite powdery.

What was in there originally? Would it be best left with a paint finish, or does the thin layer of underseal provide some sort of heat / noise reduction properties.

I'm not looking for a concours finish, just something presentable!

 

[portland_bill]

No idea what was there originally, but I'd be a bit worried about anything bitumen based, due to flammability.
Hopefully a knowledgable owner will be along shortly, and surprise us both.

 

[fiat500]

With the engine out and in pieces I decided to sort out the inside of the engine bay, but I'm trying to work out how it was originally finished. I've started scraping off the 'stuff' on the panels, and so far I've found 3 different paint colours, and probably 2 or more coats of some sort of underseal The one nearest the surface is really quite rough and looks as if its been applied with the sort of machine used to pebbledash houses, it also appears designed to retain as much muck as possible. Farther down there seems to be some sort of smoother finish, possibly bitumen based which either comes off in flakes or has gone quite powdery.

What was in there originally? Would it be best left with a paint finish, or does the thin layer of underseal provide some sort of heat / noise reduction properties.

I'm not looking for a concours finish, just something presentable!

The original finish is a fairly cheap and roughly applied, bitumen-based compund which was probably intended to cut down resonance of the panels. It looks like modern stonechip paint and some people have repainted using that after scraping the old stuff off. I have attached an old image which shows part of the untouched surface on my car. The top-coat colour is painted over the rough surface and bleeds through in places, and not much attention was made to make a neat and complete coverage.

 

[paul in manche]

Thanks very much for the photos, really helpful. Ours looks like that only rougher - perhaps it was done by some spotty apprentice!
It also confirms that ours is missing the bolt on panel on the distributor side, I'll have to add that to my shopping list.

 

[Bounding Bambino]

As far as what the original finish was, thats a good question, i personally have not been able to find what these cars had from the factory. With that said, being in the modern times we are in now, there are some fantastic products out there designed for these types of applications.
I have been doing research and planning what my protection coating system will be. I have basically narrowed it down to what they call "euro undercoating" here, which is basically a flexible / rubber high build spray on smooth texture coating that is found on alot of higher end German cars. A good friend of mine restores classic 911's, and its what they used at the factory and what he uses during restoration (just a better modern version then in the 60's). Its top coat paintable.
I plan to do the entire engine bay, bottom pans, and inside the front trunk with the coating before doing my colour paint coats. Not only does it provide water ingress/ abrasion protection, it also add sound damping/heat protection, which would help with the cabin environment.

 

[paul in manche]

I knew I shouldn't have done too much poking around in there, found a section of what appears to be the Italian equivalent of 'pigeon ****' welding on the inner wheel arch near the bump stop, another job to add to the list.

 

[Stan1970]

I just had my engine out and decided to paint the engine bay flat black since I didn't have the time to have the body shop paint it to match the car. I did remove all the undercoat and white peeling paint off before I painted it. I think it came out pretty good.

 

[Bigvtwin996]

From what I can gather on early cars it was a very thin bitumen type paint....
really didn't do much other than provide a matt surface for water....

Personally I do like what the Americans call Load Bed paint, which I believe comes in basic colours but can be over painted.....
I don't think a thick coat of anything would really do much regarding sound deadening, so my aim will be rust prevention....
I am looking at cold galvanizing that can carry a warranty which can then be over painted with std automotive paint....

 

[Uaglio]

I removed the undercoat from mine but only to a point. Then just primed and painted over.

 

[Stan1970]

From what I can gather on early cars it was a very thin bitumen type paint....
really didn't do much other than provide a matt surface for water....

Personally I do like what the Americans call Load Bed paint, which I believe comes in basic colours but can be over painted.....
I don't think a thick coat of anything would really do much regarding sound deadening, so my aim will be rust prevention....
I am looking at cold galvanizing that can carry a warranty which can then be over painted with std automotive paint....

US here, it's called Truck Bed Coating. Great stuff! some people coat their entire vehicle with it hahaha!

 

[Bounding Bambino]

I wanted to give a small update and info snippet for those also considering doing a undercoating treatment. My application obviously relates more towards a restoration application, but depending on your needs, it might help narrow down a technique or give folks a range of products to explore. Or a way to waste a few hrs of a night looking up automotive refinishing products. lol

Like i mentioned before, i had used in the past the "euro undercoating", more specifically (ProForm brand PF 565 / PF 560 / PF 566) in my neck of the woods. This spring i began spraying some samples up on bare sheet-metal to see what textures i could get, and what type of buildup i could get. It can be a bit tricky using the can stuff to get a match coating if your doing a patch repair for example (i have done repairs on some classic porsche and benz that have this from the factory). For the majority of applications this style of spray can product would work, and 99.9% of folks would be satisfied. For my 500's plan, it just wasnt right for my needs.

A truck bed coating is a similar product, however i have seen inconsistencies with variance in the product, more towards the final hardness/flexibility, and adhesion abilities. Obviously a quality product is preferred, but that market can have some significant variance. If your going to go that route, find a name brand, or buy from a autobody shop. But it is a great alternative. Definitely easier to get.


As i am working away my 500 restoration project, a quality seam sealer product was my next research task to look into. Turns out seam sealer, and the spray euro style undercoating are basically one and the same product. Application just differs; spray vs spread. Long story short, i narrowed down to a few products. Which then snowballed into another tool, and you can guess how this went. Obviously in the US you have many more choices. I was able to get my hands on SEM 29482 seam sprayable seam sealer. They have other p/n in different colours, this is just an example for those who want to google and see. Unfortunately this type of product requires a applicator gun 29442 if you want to use it as a "textured undercoating" as well as a "sound dampener". But it gives you the adjust-ability to tune how thick and how the texture sets. There are other brands that use the exact same system. The SEM gun is made in italy, so im sure in europe there is likely a similar rebrand unit.

Here is a interesting video.


SEM and 3M has alot of neat product videos for their automotive coatings lines. If your doing a resto, these type of tech vids help with material choice and coating planning.

I know im just rambling on, but using the correct products can help keep these great cars held together longer.