ms53_wagon Posted February 8, 2010 Share Posted February 8, 2010 Hey, easy one here hopefully: was going to do a compression test on the van. but ran into a small issue that im not sure what to do about.. When i crank the engine the compression rises on the gauge and levels off at a value (cant remember what it was right now), but then - if i re-crank the engine it will jump up again on the first compression stroke, and again if i re-crank it. Its an 8 spark engine and i was doing it on the exhaust side but i didnt think this would matter? do i just compare the values i get from the first continuous crank till it levels off? Cheers Dan Quote Link to comment Share on other sites More sharing options...
KKtrips Posted February 8, 2010 Share Posted February 8, 2010 My technique for compression test is this. 1 - Get engine up to operating temp 2 - Crack off spark plugs a quarter turn each 3 - Run engine for 30 seconds at around 2-3000rpm 4 - Remove the plugs (being an 8 plug you will need to leave 1 plug in per cylinder) 5 - Disconnect the distributor to eliminate the spark 6 - Jam the throttle wide open (have someone sit in the car) and make sure the throttle stays WOT until the entire test is complete (opening and closing the throttle between compression checks causes bore wash and can alter the compression from first to last) 7 - Start on number 1 and thread the compression tester in till it is firmly seated 8 - Crank Engine over so the engine turns over 20 times (10 compression strokes) 9 - Write down the result from the gauge (generally between 100-180psi) for each cylinder 10 - Back to stage 7 but move to next cylinder and continue 11 - Compressions shouldn't alter more than 10% between worst and last (up to 20% at most) Quote Link to comment Share on other sites More sharing options...
ms53_wagon Posted February 8, 2010 Author Share Posted February 8, 2010 sick! couldnt get a better answer than that. Thats me tomorrow evening Cheers Quote Link to comment Share on other sites More sharing options...
CaMpylobacter Posted February 8, 2010 Share Posted February 8, 2010 2 - Crack off spark plugs a quarter turn each 3 - Run engine for 30 seconds at around 2-3000rpm whats the reasoning behind this? Quote Link to comment Share on other sites More sharing options...
KKtrips Posted February 8, 2010 Share Posted February 8, 2010 cos of carbon buildup around the threads at the end of the spark plug, when you initially loosen the plugs it can be dislodged and get into the cylinder - if you don't burn it off by running the engine at a load - you can get bits of carbon jamming under the valve seats and giving a false compression reading.. Quote Link to comment Share on other sites More sharing options...
CaMpylobacter Posted February 8, 2010 Share Posted February 8, 2010 makes sense Quote Link to comment Share on other sites More sharing options...
KKtrips Posted February 8, 2010 Share Posted February 8, 2010 and you thought I was leading you down the garden path.. BTW - hows the squirty pants?? Quote Link to comment Share on other sites More sharing options...
CaMpylobacter Posted February 9, 2010 Share Posted February 9, 2010 lofl. getting better. I was just bafled as to why you'd do it. maes perfect sense though. eliminating all variables Quote Link to comment Share on other sites More sharing options...
xsspeed Posted February 9, 2010 Share Posted February 9, 2010 Geez KKK thats some good info, does the tech section have a rolling delete like off topic or does it stick around - as it would be a shame to lose this/maybe I'll just write it down Quote Link to comment Share on other sites More sharing options...
SHGWAG Posted February 9, 2010 Share Posted February 9, 2010 Ever heard of a printer / copy & paste? "flock of printers" Quote Link to comment Share on other sites More sharing options...
mikuni Posted February 9, 2010 Share Posted February 9, 2010 Geez KKK thats some good info, does the tech section have a rolling delete like off topic or does it stick around - as it would be a shame to lose this/maybe I'll just write it down Why would we delete tech threads? Theres 62 pages there that you can go back through, all great stuff and it dates back to the beginning of time. We may delete the occasion post about bum wee's though. Quote Link to comment Share on other sites More sharing options...
xsspeed Posted February 9, 2010 Share Posted February 9, 2010 Why? I don't know - space constraints? - great to know it will still be here (when the time eventually comes that I'll look for it) SHGWAG - heard of laziness? Quote Link to comment Share on other sites More sharing options...
ms53_wagon Posted February 9, 2010 Author Share Posted February 9, 2010 Test complete: cylinder 1 = 190 cylinder 2 = 187 cylinder 3 = 185 cylinder 4 = 187 I think that is pretty good? all within about 3% of each other What exactly is this telling me? cylinders and rings are good?, valves are in good condition etc?? headgasket is sweet? Cheers Quote Link to comment Share on other sites More sharing options...
CaMpylobacter Posted February 9, 2010 Share Posted February 9, 2010 that's pretty sweet values. I've seen much larger differences on engines that perform fine and don't burn oil etc. Quote Link to comment Share on other sites More sharing options...
KKtrips Posted February 9, 2010 Share Posted February 9, 2010 Those look hell good mang.. Quote Link to comment Share on other sites More sharing options...
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