Triumph Repair: 79 spitfire 1500 engine, piston pin, head gasket

Question
have a knock at High RPM. Engine has been rebuilt. noise seems to be coming out of the rear of the engine. Was told years ago theat #2 piston was in backwards and it ran fine. blew engine and had to have rebuilt. they put the piston is correctly know I have the knock. Question is in respects to piston in backwards (true) ever heard of that ran 50,000 mile and no noise with it in backwards. or is something else wrong. did not replace cam or crank was told it was ok.....
Jeffrey Williamson  

Answer
Hi Jeffrey,

Most piston manufactures specify a front of a piston for several reasons. Mostly because of an offset piston pin or a split skirt design. An off set pin is designed to transfer the load of the piston from one cylinder wall to the other in a slightly different time then at the top of the stroke thus decreasing what is called "piston slap". A split skirt design requires the split in the skirt to face away from the "Thrust" face of a cylinder wall that receives the most load on the power stroke.

Neither one of these should cause a noise at high RPM when installed correctly UNLESS there is excessive ware on the piston or cylinder wall.

First you need to try to ID what cylinder is the cause. Is your oil pressure up to par? 45 psi to 70 PSI at 2000 RPM and above. If that is ok, do a cylinder kill test. Run the RPM up to when you hear the noise and short each spark plug out one at a time to see which stops the noise. Don't pull a plug wire to do the test because it may make the spark jump at the coil tower down to the primary windings and that can back track to the electronic ignition destroying it.

A piston noise can come from badly worn ring groves but that will make noise no mater which way the piston is facing.

Some Spitfires had a problem with the alignment of the head gasket and that caused the edge of the gasket to stick over a piston and at high RPM it would get struck making a piston slap noise.

Howard