Mike Jenkins Posted November 23, 2009 Share Posted November 23, 2009 Hello All. After some sound advice here, I changed the leaking head gaskets and valley gasket on my standard 1987 v8 90 and it seems to have stopped the oil, water, exhaust leaks just nicely. Wish I'd had the time/budget to replace the cam/lifters/rockers while I was there but that will have to wait. I put it all back together and discovered just how tolerant the engine is.. The timing was about 30 BTDC and it started and ran just fine (although I guess that's helped a bit by the loss of compression from the composite gaskets). The engine is original, so I'm hoping the timing marks are somewhere near where they should be. I adjusted to 6 deg BTDC and all seems fine. The vacuum advance however, is not working, and the engine has a little plastic capsule between the distributor and the manifold that the parts catalogue shows under the Stromberg diagram but not the SU (mine has SU's). It's blocked. Do I need it? What's it for anyway? Cheers Mike Quote Link to comment Share on other sites More sharing options...
MattYorke Posted December 1, 2009 Share Posted December 1, 2009 Since no one replied, I'll have a go. For acceptable running, the vacuum advance module is not required, however your mpg will worsen at light cruise. Many petrol marine engines don't use vacuum advance at all. The important bit is the mechanical advance which advances the timing in relation to engine speed (this is because as the engine revs more, the flame front speed in the combustion chamber stays the same, so it needs approximately the same elapsed time for combustion - and therefore more degrees of advance to give it the same time). I have no idea what the little plastic module is though - a guess would be some kind of damper in the vacuum circuit to dampen the vacuum advance? Quote Link to comment Share on other sites More sharing options...
Mike Jenkins Posted December 2, 2009 Author Share Posted December 2, 2009 Thanks Matt. Since the module was totally blocked, I took it out. No ill effects so far. I've since seen it referred to as a vacuum delay capsule. Not sure why you'd want to delay the vacuum advance though. The repair manuals all seem to say "check it's not blocked if fitted". None of them say when it should be fitted though. Mike Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted December 2, 2009 Share Posted December 2, 2009 The plastic module is probably a Vacuum delay valve .......... did it look like a miniature top hat ? These were used (some years ago) to improve economy and emissions ........ it would seem blocked because it is a restrictor with a very tiny office ........... this gives the effect of a step in the vacuum advance.. i.e not vac, then almost full vac......... I have seen a few on mil engines and LR export engines……….. Its Ok to bin it...........they never really worked well ! Also it might have been a non return valve. These were used to stop any carb backfire pressurre from reaching the dizzy ....... these were marked at the ends with either 'Carb' or 'Dis', some of them, also had a small red band on the carb side of the capsule..... not a very common fitment...... Quote Link to comment Share on other sites More sharing options...
Mike Jenkins Posted December 7, 2009 Author Share Posted December 7, 2009 Thanks for the explanation. I took some pictures at the weekend: It clearly says Carb on one side and Dist on the other. Either way around - it's blocked both ways, and the timing doesnt advance as the vacuum increases. So should I replace it or no? Cheers Mike Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted December 7, 2009 Share Posted December 7, 2009 File it under 'B' Quote Link to comment Share on other sites More sharing options...
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