1989 Blaster Engine Rebuild - Part 11

Part 1 - Part 2 - Part 3 - Part 4 - Part 5 - Part 6 - Part 7 - Part 8 - Part 9 - Part 10 - Part 11 - Part 12 - Part 13 - Part 14






End Gap


Two-Stroke Software Review

Part 1

End Gap

For those who are unclear about how to check the ring end gap before installing the piston kit, here's a few pictures.


I carefully place the top ring in the bore by compressing it with my fingers. It's coated with a little oil so it won't scratch either part. I hate the thought of creating scratches on internal parts.


I flipped over the piston and am using it to set the rings "square" in the bore. I gently pushed the rings down to about 12 mm from the deck. Now I'll be able to measure what the end gap is.


With my feeler gauge I select a blade that looks about right. When the metal strip is placed in the gap directly in line with the cylinder wall it is easy to tell if it's too tight or too loose. In this case the next thicker strip would not fit and the next thinner strip slid through without touching either end of the ring. After a few tries I found the one that fits correctly.


The piston ring pliers - or "thumbsavers" as they're sometimes called. Depending on the application rings can be a real pain to install. These pliers take the ache out of it along with preventing scratches and breakage due to over expansion. This pair of pliers has been used on engine bores as small as 39 mm to as large as 3 1/2" on a 6 cylinder four stroke.

Ring~

To remove the ring from the bore, slide the piston in from the other side and let its weight push it out - put a hand under it so it doesn't find the floor.

It seems as though there's no end to the details of doing a job right. Checking the ring end gap is just one of them. Wiseco calls for a minimum of .305 mm (.012") for the end gap when using this piston in this engine. Even with a bore that's properly sized the end gap measured .457 mm (.018"). That's a little on the wide side but not uncommon for Wiseco. I checked both of the rings to see if one of them was a little tighter than the other - it wasn't. If one of the rings had been .001" or .002" tighter I would have used it on the top, and let the looser ring have the bottom slot, in an effort to keep the compression a little higher. I have seen slight local seizures associated with ring end gap that's excessive - the hot combustion gasses will blow down through a wide gap, burning oil from the cylinder wall and piston while it escapes. The section of the cylinder wall that the ring end rides on is wide on this engine. Its locating pins keep it near the center of the wall as well adding a bit of safety.

These photo's also show the amount of material that has been removed from the barrel deck surface - compare these to the 4th photo in Part 3.

The engine builders of the Karting crowd would lap their rings so their top end could be broken in more quickly but for this engine running it in during a tankful of gas will work just fine.

As a side note - the Wiseco Blaster piston (66 mm) PRO-TRUE #573PS weighs 204.5 grams, 248.0 w/pin, 255.5 w/pin & rings.

1989 Blaster Engine Rebuild - Part 11

Part 1 - Part 2 - Part 3 - Part 4 - Part 5 - Part 6 - Part 7 - Part 8 - Part 9 - Part 10 - Part 11 - Part 12 - Part 13 - Part 14

 


Two-Stroke Software Review






Part 1

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