bswinn Posted May 10, 2009 Share Posted May 10, 2009 Hi guys/gals. I've done some searching both here and elsewhere online but have yet to find a definitive answer to my problem. I've recently purchased a 1977 XS 400D (Was sold as a '79 but did a little research on the VIN) and am cleaning it up and trying to restore it on a bit of a shoestring budget. I've mostly gone though every major part, disassembled it, cleaned it up, lubed it, etc. etc. MAN OH MAN are there a lot of parts. Anyways.... Recently have started in on the engine. Figured my first order of buisness before tearing it apart was to run a compression test. This is where things have been a bit screwy. The bike is torn apart so I have no way of cranking the engine over with the ignition system or anything. I suppose I could try kickstarting it, but holding onto the engine while doing this would prove a bit difficult. My compression guage is only going up to 32-35 PSI on each cylinder. That seemed REALLY low considering the compression ratio is supposed to be on order of 9.2:1. My question/concern is if this is normal because i'm only turning engine with a socket wrench? Should I try a wet test and see if the numbers are the same? Or do I just have a REALLY bad engine? Would seem odd that things would be that worn out considering the engine is 32 years old and only has 16k miles on it. Any help would be greatly appreciated. Sorry if this is the 1200th time this question has been asked. Link to comment Share on other sites More sharing options...
yoda Posted May 10, 2009 Share Posted May 10, 2009 You cannot correctly gauge the compression of an engine by hand cranking. The result will always be low. You need to follow the manual or wait until you have driven it a few miles. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted May 10, 2009 Moderator Share Posted May 10, 2009 You need to do the test either with the carbs removed or with the throttles fully open, If the bike has diaphragm carbs you are unlikely to develop enough vacuum to open the throttles by hand cranking. Link to comment Share on other sites More sharing options...
bswinn Posted May 10, 2009 Author Share Posted May 10, 2009 The carbs are completely off of the engine. But from the first reply it seems that I'm gonna need to have the engine capable of being turned over in order to properly guage the compression. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 10, 2009 Moderator Share Posted May 10, 2009 if your breaking down the engine, all you to do is measure bore wear and lap valves etc as a matter of course. If the bike has been off the road a while, the rings may have gummed up a bit skewing the readings drewps Link to comment Share on other sites More sharing options...
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