50 Determining The Cause of Bad Compression

Watch along as John Twist of University Motors determines the actual cause of the compression issue with a little demonstration.

Category:

Autos & Vehicles

Tags:

• John
• Twist
• University
• Motors
• Compression
• Valve
• MG

[Bluebelleist]

@Brock1912 A leak down test will indicate which component is failing. I think you're getting your leak down test and your compression test mixed up there. A leak down test involves introducing an air supply at around 100psi into a cylinder at TDC on the firing stroke. If an exhaust valve is at fault you'll hear air escaping down the exhaust, if it's an inlet valve then you'll hear it in the induction system and a bad ring will be heard through the crank case breather or dip stick.

[Brock1912]

A leak-down test will only tell you if the cylinder is or is not holding pressure. This test tells you WHICH component is causing the compression loss.

[mishakol129]

If you just do a leak down test you would know way faster

[gokblok]

is there a reason to do this versus a leak-down test with compressed air?

[seasonedtoker]

don't use gasoline use diesel as it won't ignite that easily with open flame. some hydrocarbons like diesel have good lubricating properties too, but yes very limited at the same time.

[063209dr]

I trust the kerosene was removed from the cylinders and the pistons relubricated. As I'd have thought kerosene will almost certainly wash any lubricant away thus leaving the pistons initially devoid of lubrication when the engine is next started.

[krazyhooligan]

water works

[zackswest1]

I sure do love these videos! I am not an mgb Owner but am freshing up on my skills as a entry level technician. Thanks a bunch keep them coming. Need a Tech??

[DALE97DSM]

great tip

[thyalone]

That is brilliant. thanks