R975 Radial engines

[Bob Phillips]

I wanted to revive this post to ask for some input from our knowledgable membership pool. I have been hunkered down at home (like many of you) for a long time now, and have been using the time to get some longstanding jobs finished. One job has been to continue to sort through and catalogue my collection of engine parts. One item I have found raises questions so here goes;
I have a bunch of sealed ring packages for the 975 that are described (in one book) as being "tinned". They are light coloured and almost look like they have been spray painted with aluminium paint. The coat seems to wear off or rub off relatively easily. I have attached photos where you can see the cast iron base material beneath the coating. These spots are not corrosion.
Does anyone know anything about tinned rings, application, pros and cons?
Any input appreciated.
C4ringsa.jpg

C4ringsb.jpg

RIngs2.jpg

RIngs3.jpg

[David Herbert]

I can only think that the tinning is for quicker bed in or corrosion resistance in storage. I have never heard of this before in any application so, sorry, not much help.

David

[Bob Phillips]

In various previous posts I have talked about chrome vs steel cylinders. One of the big advantages to chrome is their resistance to corrosion in damp or high moisture environments. I have made mention of an engine I opened up to check for damage ( and found smashed pistons, cylinder case etc) and point out that it was equipped with steel cylinders. (first photo)

you can see that the cylinder bore is badly rusted and even in the best of circumstances a steel bored cylinder will likely need some level of reconditioning to be serviceable again. So now check out the next group of photos. They show an engine, (opened up to ensure no catastrophic damage) with chrome bores. This engine was rebuilt in 1945, has been stored outside under cover in the weather extremes of Canada. You can see there is only the spattered beginnings of rust on the chrome, some of which I wiped off with an oily rag. I seems possible that the pistons may be removed without too much difficulty and may even prove to be reusable in a fresh overhaul.
The downside of chrome (as Perry pointed out in post 138) is the rings take much longer to seat and they typically use more oil. However for a tank owner who doesnt have the advantage of a temperature controlled storage environment or who doesn't start the vehicle regularly, chrome may well be the way to go. Overall, a nice engine considering it has been sitting all these years!