V7 SLR Posted June 12, 2003 Share Posted June 12, 2003 OK, I'm confused. DVA and I set the cam timing up on Saturday such that it was 100% bang on. Perfect. Car drove like it had 2 engines. Fast, powerful and very revvy. So, car apart again... nothing unusual there... and rebuilt but the cam timing is perplexing. I haven't moved the verniers' "outers" relative to the "inners" but I am getting very different results from how it was when it was last built. For example, inlet should be 130 thou and now it's 157. Unless I'm a plonker (entirely possible) if I move the inlet round a whole tooth, I get 59 thou. Does that sound right? I have replaced the belt and tensioner (for one which now has increased range - re-welded backplate), and the pulleys have come off and been put back on. I wouldn't have thought there was any way there could be a difference of 27 thou (157 now against the original 130). Surely when dealers do a cambelt change they don't re-measure the cam timing. They just pop it back on the way it came off don't they? I'm going to have another check tonight but would appreciate comments please. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
V7 SLR Posted June 12, 2003 Author Share Posted June 12, 2003 I've another idea. I can't remember exactly how DVA and I were setting these up, but it was with 3 dial gauges. Therefore is it possible that we started with the inlet cam completely OFF the follower and wind up until we got TDC on the piston-measuring dial gauge, then read off the inlet measuring vernier? Could the fact that I've only got one dial gauge and I have to use it to first set TDC and then wind backwards off the inlet follower. Could this give the difference? Looks like I need a second dial gauge. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
V7 SLR Posted June 12, 2003 Author Share Posted June 12, 2003 I have since given this some thought and don't think it applies because I always GET to TDC in a clockwise position. Therefore the inlet lift is set in the right direction. Even if I do wind it off anticlockwise, it shouldn't matter as the originaly lift was produced in a clockwise manner. When installing the cams, I noted that the pulleys lined up at 90 degrees BTDC so I *should* have got it right, no? AArrrrggghhhh. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
Mr Locust Posted June 12, 2003 Share Posted June 12, 2003 Talking to yourself is often a bad sign. Writing to yourself, now that's something entirely different... 😬 Link to comment Share on other sites More sharing options...
Mr Locust Posted June 12, 2003 Share Posted June 12, 2003 There was an article in LF a few months on this by the way Link to comment Share on other sites More sharing options...
V7 SLR Posted June 12, 2003 Author Share Posted June 12, 2003 Friend "in the know" has advised me that there are enough tolerances when removing and replacing the crank primary pulley (cam belt) that it is entirely possible that my settings have "drifted" and that I ought to reset the cam timing. Seems sensible so I will. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
Rob Walker Posted June 12, 2003 Share Posted June 12, 2003 Nig , Looks to me that you should leave the cam timing to someone who knows what hes doing before you spoil your engine good and proper. You should have no problem in gettng the timing right with one DTI . Edited by - Rob walker on 13 Jun 2003 08:38:09 Link to comment Share on other sites More sharing options...
V7 SLR Posted June 13, 2003 Author Share Posted June 13, 2003 Rob, that was harsh and unfair. If you bothered to read my posts I was not asking how to use a dial gauge nor how to do cam timing. I was questioning whether there are any circumstances (as described) which could give rise to a change in cam timing. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
V7 SLR Posted June 13, 2003 Author Share Posted June 13, 2003 Besides which, I've got it all sorted now. Driven to work and it's all fine. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
Rob Walker Posted June 13, 2003 Share Posted June 13, 2003 Sorry Nig I agree twaz abit strong. Variations in readings can be down to slack in the cam belt and the poor sloopy fit of the alignment key on the crank gear to the front pulley. Link to comment Share on other sites More sharing options...
V7 SLR Posted June 13, 2003 Author Share Posted June 13, 2003 😬 Actually I had a fright when I removed the crank sprocket. I noticed that as well as it having a "flat" where it keys to the crank, it has an indentation similar to the key between the sprocket and the alternator belt pulley. I have heard of woodruff keys and thought perhaps one should exist there... only I couldn't find it anywhere. Must have covered my entire garage floor on my hands and knees before giving up. Friend called me later that evening and confirmed there wasn't one. I felt a bit of a berk at that point. Glad no-one was watching me earlier. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
R2D2 Posted June 13, 2003 Share Posted June 13, 2003 V7, just a couple of details to try to worry you even more. Did you adjust the valve clearances before you fiddled with the timing? Have you set the clearances on the inlets and exhausts to consistent values? For example I have just been timing up an Imp engine and the valve clearances for an R23 race cam are 10-40 thou on the exhaust. I am convinced that if you use this tolerance range within a single engine it will not run very well. The clearances of the pairs of valves in a four valve engine are also very important and if the inelt pairs are at the extremes of their tolerance it won't produce optimum levels of performance. Valve clearance must have some effect on timing and BMEP so they need to be very consistent within and individual engine. Link to comment Share on other sites More sharing options...
V7 SLR Posted June 13, 2003 Author Share Posted June 13, 2003 If by "valve clearances" you mean the gaps betwixt follower and cam then the answer is a resounding YES... this has been the problem which has plagued me for ages. On Saturday I went to DVA Towers to finally lay to rest the ghost of rattley tappets. It resulted in a very impressive and quiet (at last) set of gaps. The car appears to run well again. I'm happy now. Italy holds no fear. 😬 Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
oilyhands Posted June 13, 2003 Share Posted June 13, 2003 Chris, It used to be common practice on Imps and some other engines to vary the follower gaps to cut the duration down or increase it a little, 10-40 does seem a little excessive, 30thou is probably 3-4 degrees of duration which would be lost at either end of the lift curve. Nigels follower gaps are within 1 thou of the recommended tolerances , 8 thou inlet, 10 thou exhaust. Davbe Link to comment Share on other sites More sharing options...
R2D2 Posted June 14, 2003 Share Posted June 14, 2003 Oily, Bad typo, meant to say 10-14 thou, but I agree that you can run the R23 with slightly tight gaps and it seems to soften up very lightly. When I checked my engine last week the gaps varied from 2 to 11 thou and I have now set them all to 12. Sorry for the cock up. Link to comment Share on other sites More sharing options...
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