
PETROL ENGINE COMPRESSION TEST KIT
3PC
MODEL NO: CT951.V4
Thank you for purchasing a Sealey product. Manufactured to a high standard, this product will, if used according to these
instructions, and properly maintained, give you years of trouble free performance.
IMPORTANT: PLEASE READ THESE INSTRUCTIONS CAREFULLY. NOTE THE SAFE OPERATIONAL REQUIREMENTS, WARNINGS & CAUTIONS. USE
THE PRODUCT CORRECTLY AND WITH CARE FOR THE PURPOSE FOR WHICH IT IS INTENDED. FAILURE TO DO SO MAY CAUSE DAMAGE AND/OR
PERSONAL INJURY AND WILL INVALIDATE THE WARRANTY. KEEP THESE INSTRUCTIONS SAFE FOR FUTURE USE.
1. SAFETY
WARNING! Ensure all Health & Safety, local authority and general workshop practice regulations are strictly adhered to when using
tools.
8 DO NOT use tester if damaged.
8 DO NOT use the tester for a task it is not designed to perform.
9 Maintain the tester in good and clean condition for best and safest performance. Use an authorised service agent.
9 Wear approved eye protection. A full range of personal safety equipment is available from your Sealey stockist.
9 Wear suitable clothing to avoid snagging. Remove ties, watches, rings and other loose jewellery and contain long hair.
9 Maintaincorrectbalanceandfooting.Ensuretheoorisnotslipperyandwearnon-skidshoes.
9 Account for all tools and equipment being used and do not leave them in, on or near engine.
9 Keep the work area clean, uncluttered and ensure that there is adequate lighting.
8 DO NOToperatethetoolwhenyouaretiredorundertheinuenceofalcohol,drugsorintoxicatingmedication.
9 When not in use, place in original protective case and store in a safe, dry, childproof location.
9 Always refer to the vehicle manufacturer’s service instructions or a proprietary manual, to establish the current procedure and data.
2. INTRODUCTION
Largeeasytoreadgaugewithimperialandmetricreadings.Sidereleasevalveand12”exiblehoseforeasyreach.Pressurerange
0-300psi/0-2000kpa.Screwin14and18mmadaptorsand150mmrigidstemconeadaptortsmostsparkplugholes.Suppliedinstorage
case.
3. OPERATION
3.1. PREPARATION
3.1.1. Run engine until normal operating temperature is achieved.
3.1.2. Stop engine, loosen spark plugs one turn, with an air hose, blow dirt and debris from the spark plug wells.
3.1.3. Remove all spark plugs.
3.1.4. Ifttedwithacarburettorsetthethrottlevalvewideopen.
WARNING! The ignition system MUST be disabled. Failure to disable could result in damage to the ignition system or ECU.
3.1.5. Unplug the low tension connections to the coil. If you aren’t sure how to disable the vehicle ignition system then consult the
manufacturer’s service instructions or a proprietary manual before you start. It is also good practice to unplug the fuel injectors or
disablethefuelpump,especiallyoncarsttedwithacatalyticconverter.Thispreventsunburnedfuelgettingintotheexhaustsystem
during the test.
3.2. COMPRESSION TEST
3.2.1. Usingtheappropriatethreadedadaptor,screwthetester(g1),intoasparkplughole(nger-tight-donotuseawrench)orusing
thepushtting(g2),holdthecompressiontesterrmlyagainstthesparkplugaperture.
3.2.2. Cranktheengineuntilnoincreaseinpressureisnotedonthegaugereading;usually3or4revolutionsissucient.Takeanoteofthe
pressure reading.
3.2.3. Decompresstesterbypressingreleasevalve(g1)removethecompressiontesterfromthesparkplugholeandproceedtothenext
cylinder. Note pressure reading for each cylinder.
NOTE: Theactualgureinpsiisnotimportant.Itisimportantthatallcylindershaveapproximatelythesamecompressionpressures.
Onhighcompressionengines(150psiandhigher)thepressureshouldnotvarymorethan15psifromthehighesttothelowest
cylinder reading.
Onlowcompressionengines(under150psi)thepressureshouldnotvarymorethan10psifromthehighesttothelowestcylinder
reading.
NOTE: Compression readings are unbalanced when one or two cylinders are considerably higher or lower than the others.
3.3. CAUSES OF UNBALANCE
3.3.1. Low cylinder compression is caused by leakage from:
A.HeadGasket-explosivesoundwhenrunningengine.
B.HeadGasketbetweencylinders-compressionwillbelowintwoadjacentcylindersandwatermayappearincylindersor
crankcase.
C. Valves that are not seating properly.
D.Pistonringsthatareworn.Pourateaspoonofoilintothesparkplugholetosealtherings.Repeattest.
CT951.V4Issue111/03/22
Original Language Version
© Jack Sealey Limited
Refer to
instructions
Wear eye
protection
Wear protective
gloves
Wear safety
footwear
Wear protective
clothing

If compression reading increases, the rings are worn; no increase indicates a bad valve.
3.3.2. High cylinder compression is caused by accumulation of carbon in that cylinder. High compression readings in all cylinders is
causedbyanevenaccumulationofcarboninallcylinders.Thismaycausedetonationpinkingthatisdiculttoeliminate.
CT951.V4Issue111/03/22
Original Language Version
© Jack Sealey Limited
Sealey Group, Kempson Way, Suffolk Business Park, Bury St Edmunds, Suffolk. IP32 7AR
01284 757500 01284 703534 sales@sealey.co.uk www.sealey.co.uk
Note: It is our policy to continually improve products and as such we reserve the right to alter data, specifications and component parts without prior
notice. Pleasenotethatotherversionsofthisproductareavailable.Ifyourequiredocumentationforalternativeversions,pleaseemailorcall
ourtechnicalteamontechnical@sealey.co.ukor01284757505.
Important: No Liability is accepted for incorrect use of this product.
Warranty: Guarantee is 12 months from purchase date, proof of which is required for any claim.
ENVIRONMENT PROTECTION
Recycle unwanted materials instead of disposing of them as waste. All tools, accessories and packaging should be sorted, taken to
a recycling centre and disposed of in a manner which is compatible with the environment. When the product becomes completely
unserviceableandrequiresdisposal,drainanyfluids(ifapplicable)intoapprovedcontainersanddisposeoftheproductandfluids
according to local regulations.
g.1
g.2
