neo Posted March 31, 2009 Report Share Posted March 31, 2009 Hi All I've measured the piston ring gap and I'm getting Top Ring Gap 1.3mm Bottom Ring Gap 0.5mm The fact that they are different I assume they both need replacing. But what should the gap be? Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
stork955 Posted March 31, 2009 Report Share Posted March 31, 2009 Gday Neo, rule-of-thumb is 4 thou per inch of bore size (0.1 mm per 25 mm - a 75 mm bore should have around 0.3 mm gap). A little bit too much is better than too little. Also make sure the ring is square in the bore for checking - I do this at the base (unworn) end of the pot and use the piston to gently set the ring square in the bore. Keep the gap out of the ports. Also check ring side clearance (up-and-down) in the ring groove - about 8 thou (0.2mm) is getting too big. Obviously make sure the ring groove is clean first. Problems here mean a new piston. Cheers, Stork Quote Link to comment Share on other sites More sharing options...
trialsnutterman Posted March 31, 2009 Report Share Posted March 31, 2009 Make sure the rings aren't tapered before checking side clearance. The 290 rings are definitely tapered so you can't check them as the gap depends on how far in the rings are. Stork955 do you know any way of checking side play with tapered rings? Quote Link to comment Share on other sites More sharing options...
neo Posted March 31, 2009 Author Report Share Posted March 31, 2009 Awsome information gents. Stork is "bore size" the diameter of the cylinder? Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
copemech Posted April 1, 2009 Report Share Posted April 1, 2009 (edited) From the RYP site. ".001 US on the piston/cyl and .020 on the ring gap." (in inches) Take that as you like, as I presume these are new limits(or near). ? Edited April 1, 2009 by copemech Quote Link to comment Share on other sites More sharing options...
neo Posted April 1, 2009 Author Report Share Posted April 1, 2009 Thanks Cope, But I'm I missing something?....I keep going to http://www.rypusa.com/ but I can't see any Technical information anywhere Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
stork955 Posted April 1, 2009 Report Share Posted April 1, 2009 G'day, Bore size is the diameter of the cylinder, and no, I have no idea how to check side clearance on tapered rings. I haven't even seen any for years so its lucky that fact was pointed out. A bit of research in my trusty ACL Rings book calls them Trapezoidal or Keystone rings and reveals this - Keystone and trapezoidal rings are sometimes used in engines with chromium plated bores. Always check that any chromium plated ring does not go into a chromium plated bore. Note also that tapered side rings will appear to have too much side clearance when fitted to the groove. The correct position to check for side clearance is when the ring outer face is flush with the land. In this position the ring must still have side clearance. Note: Some tapered side rings have a bevel on the outer edge to neutralise any twisting which might otherwise cause high blowby. These rings will still have the dimple the dimple or letters to designate top. I probably knew all that when I was at tech,so long ago now... Trapezoidal rings have only the upper face tapered, Keystone are tapered on both the top and the bottom. The book says that side clearance should not exceed 3 thou with the face flush with the piston. I also forgot to mention back clearance - making sure the ring goes right into the groove in the piston. There is a spec, but usually I just make sure I can push the ring below the face of the piston. HTH Cheers, Stork Quote Link to comment Share on other sites More sharing options...
copemech Posted April 2, 2009 Report Share Posted April 2, 2009 (edited) Thanks Cope,But I'm I missing something?....I keep going to http://www.rypusa.com/ but I can't see any Technical information anywhere Best of balance. Neo Neo, that info was posted by Ryan in the Forum threads under tech help or something! The only way I know to get a personal measure is to put a new ring into the unworn section of your bore. Does sound as though you need a top ring! Edited April 2, 2009 by copemech Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.