compression test

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16Cabulrd
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compression test

Post by 16Cabulrd »

can you please advise whether I would obtain accurate compression results by spinning a removed engine on the starter with fully charged battery and all plugs removed and with no carb fitted?
Big Daddy
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Re: compression test

Post by Big Daddy »

Compression readings should be valid but your biggest problem is securing the engine against torque reaction from the starter motor. At best the engine will rock which will unseat the compression tester, at worst the engine will fall over :!:
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Dave Clark
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Re: compression test

Post by Dave Clark »

But if you lay it on it,s side, perhaps against a block of wood, an then stand on it while cranking it will be fine - I know, I ,ve done it.
Big Daddy
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Re: compression test

Post by Big Daddy »

Dave Clark wrote:But if you lay it on it,s side...
Just wondering where oil in the sump might flow... :whistle:
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Dave Clark
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Re: compression test

Post by Dave Clark »

Details, details .

There will be enough oil flowing around to do a compression test, surely ?

Never seemed to do any harm when I tried it anyway. (But when I last resorted to this I think I was about 21, so probably didn,t even think about it !!)
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Neil Evans
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Re: compression test

Post by Neil Evans »

Could always ratchet strap it to a bench leg or other suitable post...
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Big Daddy
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Re: compression test

Post by Big Daddy »

Dave Clark wrote:Never seemed to do any harm when I tried it anyway.
Yes you would probably get away with it 90% of the time... :whistle:
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A40FARINAGURU
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Re: compression test

Post by A40FARINAGURU »

i've fired them up on the floor with no restraints :thumbs:
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Big Daddy
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Re: compression test

Post by Big Daddy »

A40FARINAGURU wrote:i've fired them up on the floor with no restraints :thumbs:
Sounds dodgy to me especially if the fuel supply gets damaged. An old friend temporarily fed an A-Series from a metal can which he kicked over resulting in a fire. His wooden garage burnt down taking his Mini with it... :whistle:
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16Cabulrd
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Re: compression test

Post by 16Cabulrd »

I had already tested 4 removed engines without any restraint without them moving and remaining upright; my question was actually to establish whether they spun fast enough to obtain accurate compression tests? it appears the answer is yes.
Big Daddy
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Re: compression test

Post by Big Daddy »

16Cabulrd wrote:...my question was actually to establish whether they spun fast enough to obtain accurate compression tests?
No you never mentioned that question. What makes you think it would spin slower whether installed or removed from the car :?:
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16Cabulrd
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Re: compression test

Post by 16Cabulrd »

Because nutty as I can be I thought you removed one plug at a time and started the engine to get an accurate compression, I'm 79 and obviously am losing the plot. I must be as at my age to take on two major restorations, but at least it gets me away from her indoors.
Big Daddy
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Re: compression test

Post by Big Daddy »

16Cabulrd wrote:... but at least it gets me away from her indoors.
Good on you... :thumbs:
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Bill
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Re: compression test

Post by Bill »

If all the other plugs are out then there should be no problem with oil starvation or the starter having to work too hard to spin it. Inlet configuration should not matter because compression measured with both valve closed. Or am I wrong again?
Big Daddy
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Re: compression test

Post by Big Daddy »

Sounds fine to me. If you discover a cylinder down on compression, an additional Wet Compression Test can help diagnose the problem:

http://www.freeasestudyguides.com/compr ... g-oil.html
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