6 replies to this topic

[The Matt]

hi peeps,

What is the recommended maximum and minimum ring gap for the powermax 73.5s, I can't find owt!

[The Matt]

Does 0.009" sound correct???

[Sprocket]

Well the SAE Recommendations chart with my Total Seal rings says for 73.5mm bore it should be between 0.008" and 0.016"

[The Matt]

I was trying to work it out and convert from metric (feeler guages) into thousands of an inch lol.

I read that you generally allow 0.0035" per inch of bore diameter, so at 2.89" diameter I made it 0.010"ish. Which is like 0.254mm. Either way it's new ring time as I measured a nice big 0.8mm gap when the ring was 75mm down the bore (pushed down with inverted piston).

[Guess-Works.com]

My rule of thumb < 12 tho ok, 12 - 15 tho ok ish > 15 tho new rings/possible rebore

[The Matt]

My rule of thumb < 12 tho ok, 12 - 15 tho ok ish > 15 tho new rings/possible rebore

Thanks John,

Well, I have decided to order a new set of rings (standard size) from Minispares today and I am going to send off one of my spare A+ blocks for an offset rebore to 73.5mm. It'll only cost me £80 for the offset rebore, so it really makes sense to get it done now. I'd feel happier using an A+ block to be honest as this current 1380 is an A series and hasn't been offset bored so there's no life left in it.

It was still a good bargain though at £35. The pistons themselves are in really good condition and the crank journals are all at standard (though they will have a -0.010" re-grind if it gets used in another project. Using the alternative block will balance things out a little in the garage too. I have a freshly reground A+ crank to use in the 1380 which is now going to be an A+ block. Then the spare A series crank can be reground and used in the 1400 A series block!!! Confused now? Try being me!

[Sprocket]

Sounds like a plan