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Pistons for iron SQ4

Posted: Fri Feb 08, 2019 12:48 pm
by Pete.Silson
I am looking for pistons for an iron 4G. My bores are currently +0.020" but are in need of a rebore. I am investigating a number of options but would appreciate some advice/experience please. My choices seem to be:

  1. Source some decent used (or NOS) standard pistons;
  2. Use Draganfly Mk2 +0.040" pistons;
  3. Use IMD Mk2 +0.040" pistons.
I have looked at some used hepolite pistons but, by the time I factor in new rings and gudgeon pins, the cost would be more than the new Mk2 pistons. I would however prefer to keep the low compression feel to the 4G engine.

Draganfly says that Mk2 pistons will up the compression of a 4G engine to 6.9:1. Has anybody had experience of machining Mk2 piston crowns flat to keep the compression ratio closer to the standard 4G ratio of 5.8:1?

What is the difference between Draganfly and IMD pistons?

Thanks in advance, Pete

Re: Pistons for iron SQ4

Posted: Fri Feb 08, 2019 8:04 pm
by paul.jameson
Hello Pete,

Some kindly soul recently mentioned a set of +0.060 NOS low comp pistons for sale on this forum. They will shortly go into my 4G as it smokes somewhat at present. The current pistons are + 0.030 low comp and have done about 2000 miles in this engine, with excellent results on at least 2 cylinders. I know there is pitting on at least one of my bores which probably explains the smoking issue. You are most welcome to come and see whether these pistons might suit your engine and I am quite happy to dismantle my engine whilst you are present so that we can assess whether it is the bores which are a problem, or whether the pistons have had their day. I did take them out of another 4G engine some years ago but my view is that they have life in them yet (as the other 4G engine had valve guide problems).


Re: Pistons for iron SQ4

Posted: Sat Feb 09, 2019 10:54 am
by Pete.Silson
Great offer Paul, I'll PM you to arrange a time. Pete