Blistering to inside of left hand valve cover

NicD · Jul 8, 2018

2008 bike, 40k miles. Since valve clearances last done it has developed blistering to bottom inside surface of left hand valve cover. Bike never runs hot on temp sensor and haven't had it low or high on oil.

Photos attached. Anyone else encountered this? Thoughts appreciated

Bendy toy · Jul 8, 2018

I've seen the oil varnish flaking away like that but has this been repainted?

patzx12 · Jul 8, 2018

It there paint inside the cover?
If there was I would clean it back to bare alloy.
I de-chromed the engine covers of my old Triumph, I wasn't too worried about the external appearance but didn't want bits of chrome flaking off the inside and floating around inside my engine.

Bendy toy · Jul 8, 2018

If you want to strip the OEM paint it will need to go to a powder coaters and chuck it into their stripping tank for a while. You "can" DIY remove the paint by soaking in cellulose thinners, but it's a tedious job and only really softens the stuff.

NicD · Jul 8, 2018

Thanks for responses. It has whatever finish was applied by the factory.

From the responses it looks like no one else has come across this. If anyone has, I would be keen to hear. In particular, I don't just want to fix this only for it to reoccur owing to some underlying problem (although low quality part seems the most likely explanation to me).

In terms of stripping and repainting, that is going to be a real faff. The fins on the inside will make it hard to strip properly and to re-finish.

Pukmeister · Jul 8, 2018

Its probably the magnesium gassing off beneath whatever coating is applied at the factory. I've heard of similar issues with magnesium wheel rims being coated.

A major issue for enthusiasts trying to refurbish mag alloy wheels is bubbling paint or powder coat due to magnesium porosity and gassing ( as is microscopic porosity causing slow tyre deflation).

Red oil residue........Castrol ??

Santa-2512 · Jul 8, 2018

Pukmeister said:
Its probably the magnesium gassing off beneath whatever coating is applied at the factory. I've heard of similar issues with magnesium wheel rims being coated.

A major issue for enthusiasts trying to refurbish mag alloy wheels is bubbling paint or powder coat due to magnesium porosity and gassing ( as is microscopic porosity causing slow tyre deflation).

Red oil residue........Castrol ??

Just thinking the same

Cant have done many miles

NicD · Jul 8, 2018

First photo is at oil change. I depressed a couple of the blisters as you can see in photo. Then took second photo after oil change and about 50 miles. Didn't make sense to lose the oil. Motul fwiw

Bendy toy · Jul 9, 2018

NicD said:
In terms of stripping and repainting, that is going to be a real faff. The fins on the inside will make it hard to strip properly and to re-finish.

Stripping the finish is easy. Take it to an alloy wheel refurb company and have them use their chemical strip tank. Then ask them to give it a gentle grit blast to etch the outer surface.

Epoxy prime and paint.

I had problems initially with paint going crinkly. The mistake was painting directly on the etch primer. It needs normal primer over the etch. Epoxy primer worked in one coat.

Don’t forget to paint the joint face. Leave that bare and there will be a ready route for corrosion.

NicD · Jul 10, 2018

What top coat would you recommend for the inside of an engine cover?

Bendy toy · Jul 11, 2018

Don’t paint it inside.

NicD · Jul 11, 2018

I'm a little confused. I have blistering to the inside surface of the cover. You posted about stripping and painting in your prior post. Was that only regarding the exterior? If so, the exterior of the cover is mint - my question is about the inside surface as per the photographs. Thanks

Bendy toy · Jul 12, 2018

NicD said:
I'm a little confused. I have blistering to the inside surface of the cover. You posted about stripping and painting in your prior post. Was that only regarding the exterior? If so, the exterior of the cover is mint - my question is about the inside surface as per the photographs. Thanks

The missing important bit (or I didn't see that).

I painted mine because the OEM paint was crazed. Then my new top coat reacted with the primer so I had to strip the whole thing. Paint stripper didn't touch it, but cellulose thinners made the coating go cheesy and I was able to scrape it off. But its messy and time consuming.

If yours is the cast metal gassing, it's almost certainly limited to just these blisters. Scrape away the damaged paint from blistered area and leave the metal bare.

Pukmeister · Jul 12, 2018

I thought the rocker covers were powder coated externally and bare metal inside. It may even have a chemically etched and protective coating rather than paint ?

Can't say I would be overly worried about it if the blisters are solid and not bubbling.

NicD · Jul 12, 2018

I depressed two of them, refitted cover, and the depressed areas enlarged again. See photos above.

My concern with scraping them off is that I then won't be able to seal the edges where i have removed the blisters. As it is my main transport I don't want to experiment and end up having to ride the bike if I am not happy with the cover.

In the end I bought a replacement cover. Found new one at a decent price and in the right colour. Will fit this evening and will then try scraping the blisters off and see how it goes.

May be unnecessary but seems prudent thing to do

Bendy toy · Jul 12, 2018

I don't mean to be rude but why is it prudent to replace the cover? There is no weather in there for the paint to protect against and the new cover could just as easily develop its own bubbles. The internal paint is simply an artefact of the manufacturing process. Nothing more.

Squashing the bubbles and putting it back, risks cracking the paint and making it even more likely to fall off. Simply scrape off the loose paint and be done with it.

NicD · Jul 13, 2018

Because if the blisters result in the finish layer coming off then there would be material making its way around the top end of the engine. Once some parts come away the probability of further deterioration of the inside surface increases. And I can't easily check this. But that's just my judgement. If you think otherwise then that's your call.

Not sure what you mean by "an artefact of the manufacturing process". Do you mean that the factory-apllied finish is unnecessary; just a by-product?

There wasn't any logic to depressing the bubbles and replacing. I just wanted to see if they were solid or not. I had to replace the cover as I needed to ride the bike. I then re-checked the cover about 50 miles later to make sure nothing had come away.

NicD · Jul 13, 2018

This is a photo of the factory finish on the inside of the new valve cover

Bendy toy · Jul 13, 2018

NicD said:
Because if the blisters result in the finish layer coming off then there would be material making its way around the top end of the engine. Once some parts come away the probability of further deterioration of the inside surface increases. And I can't easily check this. But that's just my judgement. If you think otherwise then that's your call.

Not sure what you mean by "an artefact of the manufacturing process". Do you mean that the factory-apllied finish is unnecessary; just a by-product?

There wasn't any logic to depressing the bubbles and replacing. I just wanted to see if they were solid or not. I had to replace the cover as I needed to ride the bike. I then re-checked the cover about 50 miles later to make sure nothing had come away.

The covers are electrostically powder coated so some coating will get inside though not as much as the outside. It's presence inside is an artefact of the powder coating process.

I would have thoroughly scraped away all failed paint before riding the bike. It would take a few minutes only. A replacement cover having been made in the same factory is likely to have the same risks of paint failure, so if the outside finish is good there's not much point in replacing the cover.

NicD · Jul 13, 2018

I don't think that's right. The interior finish is an even coat which has been aplied to all but the mating surfaces as you can see in the photos. It is not just an exterior coat which has been applied to some of the interior. Further, I very much doubt BMW are incapable of isolating the exterior surface when paining it!

Regarding how to deal with the blisters, I think your idea is a bad one. If you scrape away some of the surface then you lose the integrity of that surface and allow oil and heat to penetrate under the remaining surface via the hole you have created in that finish. Same as if you chip the outer surface of exterior paint - unless you reseal it, it create problems.

In any case, I'm just documenting what I did and why. If you encounter the problem, I have no doubt you will deal with it as you see best.

Blistering to inside of left hand valve cover

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