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piston rings

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oxford

Jedi Hopeful
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Hi everyone
What is the consensus on the 5th piston ring fitted below the gudgeon? Is it a good idea to fit it or leave it off? It seems to me that it would result in less oil in the bores and lubrication of the pistons and gudgeon pins. I've also heard that they can cause some drag. Any ideas?
Matthew
 
They were quite common at the time and wouldn't be there if they weren't necessary, so I wouldn't leave the lower ring off because they worked fine. However if you buy new pistons with three rings, they'll be fine too because that's what they were designed for.
 
I usually substitute a Low-Tension 3-piece oil control ring, instead of using the cast 1-piece high-tension (and high drag) oil ring.

You can buy individual rings from Total Seal, and I haven't built an engine without using Total Seal's "gapless" 2nd rings in over three (>3) decades.

I would also recommend heat-shielding the piston crowns (helps to keep the oil cooler too) and the skirts with a dry-film lubricant. Treating the skirts also reduces drag, and virtually eliminates scuffing on cold starts__of particular benefit to cars that aren't driven daily.

Here's some Healey pistons that were done for a couple of board members:

IMG_5945.jpg


IMG_5950.jpg
 
Randy,
What is the difference between your heat shield treatment and something called a teflon treatment? I just bought a set of pistons that came with the teflon treatment but they don 't really say what it does.
One more comment. We bought pistons and rings on a sale last December for 3 engines. Two TR3/4 and one MGB. The oil rings on two of the cars lost the tension and started pumping oil into the cylinders. The third car is not driven yet. When the pistons were pulled, there were two tabs that bump against each other that had broken off, these kept the tension on the oil ring. We replaced the rings with a different brand and had no problems. The replacement brand was Hastings. Original brand that came with the pistons was Dewes (we think).

jerry
 
Last edited:
Matthew,

You almost certainly have aftermarket/budget pistons if they have the lower oil ring groove. As far as I know the original factory ones never had it. The reason for it as best as I can make out is that it is cheaper to produce two single-piece cast oil rings than make a single multi-piece one that actually works.

If you use decent rings then you don't need the lower oil ring. Total Seal gave me this info when I ordered their gapless second ring set for a std bore 2639cc engine:

"our part # is S0885 3.125" 3/32 3/32 3/32 3/16 6cyl $233.96 + shipping need 5-7 day lead time to complete. "

piston.JPG

Aside from using good quality rings, it is also important to have the hone pattern done correctly for the rings and to bed them in using appropriate oil "like you stole it".

Couple of other things you might like to consider while in there- have the block deck ground down to the height of the highest piston and if the pistons are significantly different in height at TDC (mine were 20 thou different!) then have the crank index ground so they are all the same height. The reason to bring the pistons up to the top is so that the 'squish' zone in the head can work properly which means you can increase the compression ratio about a whole point without creating detonation risk.

Andy.
 
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