Subrame Restoration

[p5andrew]

I am in the process of undertaking a full rebuild of the front suspension and steering to my P5B, at the same time replacing the subframe as mine appears to have suffered accident damage in the past and is distorted.  I have a spare subframe which is in generally pretty good condition and it is currently with the shot blasters. I then have some minor corrosion damage and dents to deal with to the rear crossmember which look to have been the result of careless use of a trolley jack - all too common! 

Galvanizing the subframe would have obvious advantages in terms of longevity but would mean drilling a considerable number of vent holes which I am reluctant to do.  Galvanizing would also require a fair amount of work cleaning out all the mounting holes, tapping out the threaded holes and so forth. 

Currently, I favour etch-priming, followed by several coats of primer-filler to build up a good thickness and to help cover any minor imperfections, finishing off with three or four coats of gloss black 2-pack.  The only real potential issue with this system is that it will tend to chip quite easily.  In my working life, where we make heavy fabricated steel frames for church bells which are often housed in hostile environments, we almost invariably have our steelwork galvanized and then powder coated.  Powder coating provides an excellent finish but it too chips too easily for my liking.  

I will be very interested to hear the opinions of fellow members as to the best coating system to use.

[lagain]

Waxoyl.

The problem with any hard coating is that if moisture gets under it , it will rust.
If you want a 'detailed' underside I would suggest painting the visible parts with Hammerite (which can be touched up) and using Waxoyl on what cannot be seen and in all the cavities.
When I bought my coupe in 1975 I used many gallons of Waxoyl and due to that I still have a virtually rust free car. If Waxoyl is carefully removed from the underside of my coupe the red primer applied in the factory is still there.

[p5andrew]

Hi George

Many thanks for your thoughts on this.  

I too am a fan of Waxoyl and have used it on and off for over 40 years.  I shall certainly be using it for all difficult to reach/invisible areas while the subframe is removed and have previous injected all the box section parts of the body as well as A, B/C and D posts.  I have also Waxoyled the two doors which I have previously restored and the other two doors will follow, probably next winter now when the car is hibernating.  I have also given the wheel arches a liberal coating of Waxoyl-based underseal which has stood the test of time well.  

Hammerite (I personally prefer the smooth version) certainly has its uses and we use a similar product at work made by Coovar which is also excellent.  My concern with both products is that they chip very easily.  What I am after is a coating which is not so susceptible to this problem.

A friend has pointed me in the direction of POR15 chassis paint which I have never used.  Does anyone on here have any experience of POR15 products?  It looks quite pricey but if it does the job I am prepared to dig deep...!  

I am picking the subframe up from the shotblaster tomorrow and I plan to tackle any repairs on Saturday, so the need to get on with painting it is becoming acute!

[enigmas]

I've used POR15 quite extensively after repairs of inner panel and box sections of classic cars and Vespa scooters. The product dries rock hard and sticks like the proverbial. It is not UV stable but is generally used under cars on chassis sections and areas that aren't subject to direct sunlight. If it gets on your hands and skin it'll be there for the duration until it wears off...so do wear gloves. I've even painted POR15 over a freshly rebuilt exhaust system (not the manifold just the pipes) and it is remarkly tough, heat resistant and maintains its gloss finish.

POR15 much like very thin anti corrosion products has the ability to creep into seams and panel joins so can literally be poured into a closed section where it will work its way between joins. Rocking the vehicle after pouring the product into an internal box section will assist this process.
Yes, it is an expensive product but if you want to protect enclosed panels from moisture and the corrosive effects of salt on roads in the UK, then it is an excellent protective option in my view.

[p5andrew]

Thanks Vince.  An interesting take on POR15.  Sounds like it could be ideal for my purposes.  It is not as if 
I need gallons of the stuff so cost is not really an issue.  I just want to do the job once and do it well.  I will report back in due course.  

[MK IA Norway Viking]

Good evening - I have a MKIA built in week October 1961.

I am fitting a replacement subframe too, as the original is corroded beyong repair.

The first thing to mention is transferring the subframe number from the old subframe to the new one. This can be done by cutting out the section with the numbers stamped into it and weld the piece onto the new subframe. If done right, it will appear as original. 

I have arranged to dismantle the subframe into its individual bits, and replace the items that are worn. The only sensible time to do this is when the subframe is out, and engine etc. removed.

I am replacing the wheel bearings, brake discs, overhaul / replace calipers, brake pipes, inspect and replace as required the ball swivels and all rubber items.

I also arrange to clean up the torsion bars and lubricate with grease, followed by "sealing" them with gaiters. That way I have an arrangement similar to as-new.

The engine block is given a fresh coat of paint, and all items in the engine bay cleaned up and painted as required. 

For me, this operation is not only about ensuring the new subframe is given adequate protection, but also to bring the engine bay and the installations within to a high cosmetic and technical standard. 

As to protection against corrosion, I have taken the decision to have all steel items powder coated. It gives a great finish and is very resistant to corrosion. It is expensive, granted, but gives a great finish that give justice to the car, and will make for a long lasting protection.

Best wishes for your project.

[enigmas]

POR15 when applied to a properly prepared panel (clean and lightly abrade the surface by sanding) is tougher than powder coating. It forms a very thin tough coat that doesn't show brush marks. It dries slowly but rock hard.
In contrast, powder coating places a thick plastic like coating over the steel surface. It will also coat over fixtures and fittings with threaded holes. Theses holes will require either resizing with a drill or retapping as the coating is quite thick. When this is done the powder coating is removed. The powder coating is a plastic and far less tolerant to heat than POR15, which I have used on exhaust systems to lasting effect.

If UV is an issue POR15 can be overpainted with any type of durable top coat. POR15 can also be spray painted but the gun must be carefully cleaned afterwards with a suitable solvent. It is available in black and grey.

These are my personal experiences with both products.

[p5andrew]

Good to hear from a fellow sufferer!  


In my case, the existing subframe is not suffering from corrosion.  The reason for its replacement is mainly because measurement has shown it to be distorted, careful examination having shown that the car has at some point suffered accident damage.  I could true up the existing subframe after its removal and have the equipment and skills to do so.  However, having obtained a very good replacement subframe complete with all suspension, all the steering except the steering box and with hubs, my preference is to restore the whole lot and then swap it over.

So far, I have had the replacement subframe shot-blasted and today I have made and welded into place a strengthening plate to the underside of the central crossmember which had suffered localised damage due to careless use of a trolley jack at some point in its life.  I have also run taps into all the threaded holes to clean up all the threads.  All is now ready for painting.  I seriously considered powder coating, a process with which I am very familiar in my working life, my concern being that it tends to chip very easily.  Time will tell if I have made the right decision!

All suspension and steering components will be restored and painted.

I have already purchased a complete set of rubber bushes and suspension bushes, all new track rod joints, new anti roll bar link pins, all new stainless steel nuts, locknuts, nyloc nuts, washers and spring washers, brake discs, pads and pins.  I also have a pair Spax adjustable gas shock absorbers ready to fit.  In my case, I rebuilt and restored the calipers only three years ago but I will still take the opportunity to replace all seals.  The wheel bearings to the hubs which came with the subframe appear to have done very little work so they will be washed out, the seals replaced and repacked.  I have a set of swivel joints which I rebuilt some while ago and these will be fitted.  I have an almost new idler which will be fitted with a new seal.  

I rebuilt my existing steering box about three years ago and modified it to take an improved seal arrangement which was a success (no leaks!) so the box will be reused.  I also rebuilt the pump.

I rebuilt the engine and gearbox from top to bottom just over three years ago so all is well other than a persistent weep from the gear selector shaft which I will deal with.  All was repainted and cosmetically restored but I shall nevertheless give it a refresh.

All good clean fun!

[enigmas]

Well...how about some photos of your detail work Andrew. 😉👍

[MK IA Norway Viking]

Awesome report, gents !

the powder coating done these days is very different from earlier technology. Iam not so familiar with uploading photos on the Forum (I find it very cumbersome) so you can see pix of my subframe on the P5 facebook page. You'll see it is a thin coat which is hard. 

From the reading I see the paint suggested offering an excellent method of protection, and applaud your choice of protecting the subframe so it will last for another 60 years ... as a minimum :-)

[p5andrew]

Will certainly post some pictures, though it may be a day or three before this happens as I am currently working away from base.  


I also need to discover how to post photos to the site.  I may need to employ the services of my wife or daughters, all of whom are arguably more tech savvy than I…!

[djm16]

Shot blasting places over here automatically offer powder coating as the default immediately after blasting. If it were I, I would zinc powder coat immediately followed by low gloss black powder coat.

I have done both POR15 (polyurethane single pack) and powder coating as a first coat. POR15, even on scrupulously clean metal, tends to fish-eye like crazy.

Regarding toughness, all I can say is that the powder coating the blasting company used on all 3 sets of wheel for my 3 Rovers is extremely chip resistant and is unmarred after 10 years.

The bigger issue is the insides of the box sections. Pretty much filling the insides with waxoyl or whatever passes for it in your country is the more important process.

[enigmas]

David, POR15 won't fish-eye if you wipe the surface over with lacquer thinner first. Clean it thoroughly. Fish eyes on virtually any surface that has been painted is generally due to a poor surface prep/cleaning.

[djm16]

I hear what you say, nevertheless, after cleaning with white spirit first, then lacquer thinner I still had fish-eyes. My theory is that corroded steel, even after wire brushing, sanding and cleaning still has microscopic crevices, enough to contain contaminants and cause fish eye. Naturally YMMV.