Wrightpayne Posted July 12, 2020 Share Posted July 12, 2020 You miss my point - you have to undo the bottom pulley to get the belt off. The bottom pulley bolt clamps the toothed sprocket for the cam belt - it is this that can move and knock out the cam timing. Link to comment Share on other sites More sharing options...
revilla Posted July 12, 2020 Share Posted July 12, 2020 Ian is unfortunately correct. Once you undo the bottom pulley bolt, you can't guarantee that the timing will be exactly the same on reassembly. Link to comment Share on other sites More sharing options...
revilla Posted July 13, 2020 Share Posted July 13, 2020 This video illustrates the problem: - one tooth on the pulley is 15° and as you can see there's about half a tooth of slip there, which is the 6°-7° Dave Andrews was talking about. Worst case 6°-7° crank degrees change in cam timing is significant, especially if you have big cams and valves where clearance may be marginal. I've often wondered if it would be worth turning the cams a bit to put all the tension on the non-driven (tensioner) side of the belt before doing up the crank pulley, leaving the crank pulley as far clockwise as it will go, in which case the act of tightening it will only try to move it further in the same direction. At least then you would know it was in a specific position and when replacing subsequently you could be more sure of getting it in the same place. Not much use if you don't know it was put together that way last time. And on a tuned engine I think I'd still check the timing carefully after a belt change anyway. Link to comment Share on other sites More sharing options...
oilyhands Posted July 14, 2020 Share Posted July 14, 2020 When I assemble engines on the bench I pack the flat on the crank with a shim so that there is no radial movement in the bottom sprocket when it is fitted, Then for subsequent belt replacements there should be no introduced error.Oily Link to comment Share on other sites More sharing options...
Julian H Posted July 15, 2020 Author Share Posted July 15, 2020 HiThankyou for the enlightenment everyone. Certainly an unexpected complication.Cheers,Julian Link to comment Share on other sites More sharing options...
Julian H Posted October 25, 2020 Author Share Posted October 25, 2020 HiSomewhat belatedly, I thought it would be useful to post the outcome.The nice chaps at PGM did my cambelt / tensioner for me.Whilst I don't have enough knowledge to be sure about the reasons for the noise I suspect when my head gasket was replaced, the old cambelt was over tightened. It got hot in use and stretched slightly. New cambelt and tensioner installed correctly, noise went away!Engine now sounds perfect and back to being thrashed to 8k as normal :-)Gary, sorry I didn't think to ask to keep the old parts! It would have been useful.J Link to comment Share on other sites More sharing options...
revilla Posted October 25, 2020 Share Posted October 25, 2020 Glad to hear it is sorted. Link to comment Share on other sites More sharing options...
garybee Posted October 25, 2020 Share Posted October 25, 2020 That must be a relief Link to comment Share on other sites More sharing options...
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