molten Posted November 20, 2011 Share Posted November 20, 2011 HelloAnyone know if/how its possible to do an accurate compression check on an engine that is out of the car?Cheers Link to comment Share on other sites More sharing options...
Clive Posted November 20, 2011 Share Posted November 20, 2011 Strap a starter motor to it?Alternatively a leakdown test. I fudged one together with the spark plug adaptor off a broken compression tester and my airline. Doesn't give figures, but you find out where the air is escaping. Link to comment Share on other sites More sharing options...
Nick Jones Posted November 20, 2011 Share Posted November 20, 2011 As Clive says you can always fit a starter motor to the backplate and spin it over like that (needs to have oil in it!). You can even run an engine like this..... not saying it's a good idea - just that it's possible!Nick Link to comment Share on other sites More sharing options...
molten Posted November 20, 2011 Author Share Posted November 20, 2011 Hi FellasSo if i attach starter to ring gear, do I simply connect up a battery direct to starter or must I go via the starter silonoid?thanks Link to comment Share on other sites More sharing options...
drofgum Posted November 21, 2011 Share Posted November 21, 2011 molten,You could put the battery positive lead directly onto the starter,and control it by lifting a lead from the battery, but that makes a good sized spark at the battery. It is much safer to use the solenoid, and a small lead to activate the starter. Cheers, Paul Link to comment Share on other sites More sharing options...
TedTaylor Posted November 21, 2011 Share Posted November 21, 2011 You don't have to turn it over with a starter motor, you can do it by hand provided you have some means to turn it over such as a solid fan bolted directly to the crankshaft on some engines or a spanner on the pulley nut.Ted Link to comment Share on other sites More sharing options...
bodders1 Posted November 21, 2011 Share Posted November 21, 2011 1526 wrote:You don't have to turn it over with a starter motor, you can do it by hand provided you have some means to turn it over such as a solid fan bolted directly to the crankshaft on some engines or a spanner on the pulley nut.Teddeos this give an accurate compression test (original question at the top of this thread)? I always understood that to ge t a good compression test you had to spin the engine on the starter with the throttles wide open for a good few seconds. You're hardly likey to be able to achieve this by hand. Link to comment Share on other sites More sharing options...
molten Posted November 21, 2011 Author Share Posted November 21, 2011 I understand that each cylinder needs about three compressions before an accurate reading is provided. Is that correct?What thread size is the 1500 spark plug?cheers Link to comment Share on other sites More sharing options...
TedTaylor Posted November 21, 2011 Share Posted November 21, 2011 I thought the issue of how many times to turn the engine over would come up.I have only ever turned it over once when checking compressions because spinning it over pumps up the pressure in the tester gauge - I suppose it still does the same thing but I personally prefer to see what it is on just one turn. This is what I have done over my 50 years of car ownership because it is the method that was always described in technical publications when I first started out on the car mechanics game ...... and it has never served me wrong.Bearing in mind that very often you are doing a comparative reading of all the cylinders where you are more looking for even readings between them it probably does not really matter which method you use provided you get over the 'target' pressure in each. Advantage of 'my' method is of course that you don't need to fit a starter motor!Ted Link to comment Share on other sites More sharing options...
molten Posted November 21, 2011 Author Share Posted November 21, 2011 1526 wrote:I thought the issue of how many times to turn the engine over would come up.I have only ever turned it over once when checking compressions because spinning it over pumps up the pressure in the tester gauge - I suppose it still does the same thing but I personally prefer to see what it is on just one turn. This is what I have done over my 50 years of car ownership because it is the method that was always described in technical publications when I first started out on the car mechanics game ...... and it has never served me wrong.Bearing in mind that very often you are doing a comparative reading of all the cylinders where you are more looking for even readings between them it probably does not really matter which method you use provided you get over the 'target' pressure in each. Advantage of 'my' method is of course that you don't need to fit a starter motor!TedHi TedValid points mate. Did you ever re-test when engine up to normal operating temps to see if it made any difference after metals have expanded?Cheersscott Link to comment Share on other sites More sharing options...
TedTaylor Posted November 21, 2011 Share Posted November 21, 2011 I would do a retest if the original reading were marginal to check that things had sorted themselves out. Though the other factor here that would improve things would be that running the engine would circulate oil and free up the rings.Ted Link to comment Share on other sites More sharing options...
Freebird Posted November 24, 2011 Share Posted November 24, 2011 Nick_Jones wrote:As Clive says you can always fit a starter motor to the backplate and spin it over like that (needs to have oil in it!). You can even run an engine like this..... not saying it's a good idea - just that it's possible!NickIn ran a Mini engine like that many moons ago, more for the fun of it than anything else. I even had an oil pressue gauge connected via a plastic pipe to check my rebuild had good pressure. It did until the plastic pipe melted on the exhaust - oil everywhere ??) Link to comment Share on other sites More sharing options...
Hasbeen Posted November 24, 2011 Share Posted November 24, 2011 You want to be careful what you start, that isn't bolted down.One of the things my company did in New Guinea was engine overhaul. We had an 8 HP Yanmar single cylinder marine diesel brought in because it wouldn't go.The problem was the injector, & after it was overhauled I gave it to one of the better local native boys to refit. The engine was sitting on it's sump in the large cemented & roofed open work area. Being a good boy, he decided to make sure there were no leaks in the system when he'd refitted the injector.Unfortunately his hand slipped off the decompression lever, while he was turning it over, & it started, on about 2/3 throttle. At about 1000 RPM it was not only leaping up & down half a foot at each stroke, it was also leaping all over the work area, in large random jumps. In just a few seconds it was being chased by over half a dozen of the local boys. Of course these locals don't wear steel caped work boots, or even shoes. Each time one of them caught the thing, it would turn on him, & chase him off. It would have been great fun, if it wasn't crashing into various cars & other stuff in the work area. Finally one got it by the decompression leaver, which slowed it enough to allow another to shut the throttle.When my secretary a customer & I who had been watching all this, caught our breath from laughing, I found a couple of slightly dinged cars, some blood from a couple of slightly squashed toes, a Yanmar engine needing extensive work on it's near flat sump, & one very contrite boy. All in a mornings work up there, but none of those boys ever started an engine, without tying it up very tightly first. Link to comment Share on other sites More sharing options...
CRAJ Posted November 24, 2011 Share Posted November 24, 2011 My Dad had an 8hp Yanmar on a Marcon Tomahawk sailing boat when we were teenagers. Even in the boat you had to lift the decompression lever for 1 or 2 seconds to stop the flywheel bringing it back to life.Colin. Link to comment Share on other sites More sharing options...
sparky_spit Posted November 24, 2011 Share Posted November 24, 2011 CRAJ wrote:My Dad had an 8hp Yanmar on a Marcon Tomahawk sailing boat when we were teenagers. Even in the boat you had to lift the decompression lever for 1 or 2 seconds to stop the flywheel bringing it back to life.Colin.Ever had one of those start running on its own engine oil? I had a Petter Mini-twin in a sailing boat and motorsailing one day we caught a squall which heeled the boat right over. Suddenly the engine started racing at full revs and wouldn't stop even after coming back upright. With the fuel off and even the decompressor down (which you shouldn't really do when it's running at speed) it took ages to slowdown and eventually stop. Scary moment as we thought it was going to blow-up and catch fire. Link to comment Share on other sites More sharing options...
Steve Cureton Posted November 25, 2011 Share Posted November 25, 2011 sparky_spit wrote:Ever had one of those start running on its own engine oil? I've had it happen with my diesel campervan which I think was drawing oil from the sump via the breather, in fact it happened a few times. It's a bit scary when it happens. I eventually did an engine swap rather than trying to fix it. Link to comment Share on other sites More sharing options...
CRAJ Posted November 25, 2011 Share Posted November 25, 2011 I believe there was a problem with Renault 19 turbo diesels where a seal in the turbo would go and allow the sump oil to be drawn in. The solution was to park the car up on the hard shoulder, get out and walk away, to leave the car to go bang when it ran out of oil as the engine would be running flat out.Colin. Link to comment Share on other sites More sharing options...
redzer Posted November 25, 2011 Share Posted November 25, 2011 Had that happen in an isuzu trooper at one timeIt was my brother in laws jeep and i had been trashing it a bit so in a mad panic and getting rapidly swallowed up in a cloud of stinking blue smoke i somehow managed to stall itstarted it again after a few mins and drove home nice and slowly and quickly handed back the keys. Link to comment Share on other sites More sharing options...
molten Posted November 26, 2011 Author Share Posted November 26, 2011 my thoughts were to run on standard engine stand. Is this a good idea? Link to comment Share on other sites More sharing options...
Freebird Posted November 27, 2011 Share Posted November 27, 2011 If you fancy chasing it around the garage, yes go for it mate. ;DTo be serious, I wouldn't do that - the torque reaction from the crank spinning it likely to tip it over unless you can put a LOT of weight on the base or encase it in concrete.Glen. Link to comment Share on other sites More sharing options...
marc1estate Posted December 16, 2011 Share Posted December 16, 2011 when I worked on the scrap as a kid we used to ratchet strap engines to a bloody great tree to rum them up, not sure that would impress the huggers though nowadays :X Link to comment Share on other sites More sharing options...
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