Flathead piston ring question..

Lowsquire

Lowsquire

Member
Hi All,

Im building a basically stock 239 99A Flathead at the moment, and have run into something I cant find an answer to, maybe someone on here can help..

Im using an old set of .045 over Ford manufactured alloy pistons, four ring style.

obviously finding rings to suit these wasnt easy, but eventually I came across a set, which are Ford stamped too. Now the top and second rings are the same width top to bottom (0.93) but the depth they extend back into the piston land is different, there are two sets of eight, one are 0.142 and the thinner ones are .113 .

The piston Lands in the pistons are dimensionally identical(about.160 deep), So dont help me decide which set goes where? Im leaning towards the deeper rings at top,more pressure on the bore, and the thinking being less room behind them for carbon to build up? the second ring acting more as oil control. Is this sensible ?

any engine builders care to comment?
 
Are there any other features on the rings, dot on the end or a step cut on the inside, or the outside? My instinct is as you say, wide as top ring... Karl
 
There is probably an expander used behind the thinner ring, which would likely be fitted in the second ring groove.
 
Pete Cooper at Nordian spares here in the UK sold me a set of .045 rings recently.
they were ford old stock (very old).
I'm pretty sure the second ring had an expander behind, like a thinner version of the expander behind the oil ring.

Mart.
 
Thanks all, Thats the answer I think, the expander goes behind the second thinner ring. I thought the expanders in the set were for the third oil control ring, but apparently not!

thanks everyone.
 
Yep...expander in 2nd groove. Couldn't find anything definitive in bulletins, but this weekend at a flea market I ran into a dirt cheap NOS 99A ring set, still in the pull-the-string Ford box and instructions still within. Forgot to bring it in to work, but can do so if you need more.
wide ring top groove, narrower ring plus expander second, I believe the oil ring is 3 piece with various instructions.
Instructions do specify gap placement as well..will try to remember the sheet tomorrow.
 
Thanks bruce, I set the gap placement about a third apart for the top three rings, didnt take much notice of the bottom one. ring end gaps were zero on the fat oil rings, needed a fair bit off them. I set all the ring end gaps at .011. this is for a very low use motor (its going in a Bren Gun Carrier)
 
Ain't no low use in a carrier...that engine has to work full time all the time to move that thing! Somewhere in my collection I have an Australian maintenance manual for a 239 carrier...fascinating vehicle with very creative solutions to design.
 
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