bazzbazz 5 Report post Posted September 23, 2015 A friend brought up an interesting discussion. When using the dial gauge to find TDC, the gauge will rise till it stops, then there is a small period of "dead spot" where the crank continues but the piston is static, then starts to drop. When setting TDC for a cam belt change, where is the official correct spot? A/ When it stops rising B/ The middle of the "dead spot" C/ The moment it starts to drop Baz Quote Share this post Link to post Share on other sites
alfizta 6 Report post Posted September 23, 2015 (edited) my bet is on B Edited September 23, 2015 by alfizta Quote Share this post Link to post Share on other sites
Smaky 73 Report post Posted September 25, 2015 TDC is the centre of the "dwell" when the piston is at the highest point. The dwell is created by the lubrication gap between the big and little end shells and can be used to diagnose excessive wear within the engine. Quote Share this post Link to post Share on other sites
bazzbazz 5 Report post Posted September 25, 2015 Thanks Smaky, that's the line I have been arguing, but it is interesting to know you can use the dwell to diagnose wear. Can you elaborate s little more on that with twinspark & JTS engines? Baz Quote Share this post Link to post Share on other sites
Smaky 73 Report post Posted September 26, 2015 The longer the dwell angle the more gap (wear) there is to the bearings Quote Share this post Link to post Share on other sites
bazzbazz 5 Report post Posted September 29, 2015 I assumed that, but would you know what the min & max dwell should be as in relation to wear on the bearings? Baz Quote Share this post Link to post Share on other sites
Smaky 73 Report post Posted October 5, 2015 Different engines start with different gaps, it's hard to say but if you're getting more than 5 degrees of dwell on the TDC then it's time to think about new shells. Quote Share this post Link to post Share on other sites
bazzbazz 5 Report post Posted October 8, 2015 Much appreciated. Baz Quote Share this post Link to post Share on other sites