JM993

I never done this before on a flat six and I'm wondering how one finds TDC for each cylinder in a reasonable amount of time. It would be nice to measure each cylinder at approximately the same engine temp (or as close as possible).

I've only done this on a single cylinder motorcycle engine and used the ghetto screwdriver in the cylinder method. It worked fine, but I'm hoping there's a better way.

TIA,
Joe

Mike J

Use the rotor position in the distributor as a indicator, and then use the marks (at 120 degrees apart) on the crank pulley for the final adjustment. Easy-peasy!

When I do a leakdown, I have 6 plugs out, and just work my way around the engine while turning to each new position, based on the firing order.

Cheers,

Mike

JM993

Thanks Mike. This makes sense and should allow measurement of each cylinder relatively quickly. One more question: I would think with 6 plugs out and one cylinder pressurized to 100 psi that the engine may turn. Do you lock the engine to avoid this? Would putting the car in gear be sufficient?

Cheers,
Joe

element

I just bought a leak down tool and will do one over the next few weeks with my plug change.

Fun!

phil.

BesideTheBox

I'd like to do this on my car as well.
What brand / model of leakdown gauge tool are you guys using?
Any recommendations on a tool?

element

I bought a snap-on... found a nice new used one!

phil.

Mike J

I find it does sometime turn - seems to depend on the engine. If you have two people, one can hold it still via the fan pulley nut, or as you said, use the geartrain. You can put it in netural, rotate, put it in gear, test, neutral, etc.

As for brand, I think in some ways technique is more important, and accuracy is not going to be that close anyways (given conditions of temperature, etc). I have seen similar measurements on Milton as on Snap-on. What you are looking for is the delta between the gauge unhooked and hooked up. I always try it a few times, including tapping on the gauge to make sure it settled. I am not sure if most gauges are accurate enough to tell between say 2% and 4% leak down, that is pretty fractional. Most gauges will have their own regulator, so supply needs to be 100+ psi, but not much requirement for volume unless you have high leak down. Be consistent over the entire engine.

IF you have an issue, it most likely be obvious pretty quick - lots of air escaping, etc. Make sure you are truly at TDC though for that piston, since any slightly open valves will cause a high leakdown. If you get an issue, listen to where the air is escaping, typically out the exhaust or the crank breather - that would be valves vs. rings.

Cheers,

MIke

JM993

Mike, you were right, that was easy. Not sure how I would find TDC on a modern coil on plug design but no issues with our old style engine.

Curious about the differences between doing the test on a cold or warm engine. I'm assuming a cold engine may show more leakage as the rings probably expand when hot. I'm curious whether the opposite could be true where a hot engine shows more leakage than a cold engine.

Cheers,
Joe

Ed Hughes

You can get fancy:

http://www.stomskiracing.com/products.php?id=12

Or, really fancy:

http://www.stomskiracing.com/products.php?id=5

JM993

A fancy approach to the ghetto method. I'm guessing the stick in the cylinder method is required for coil on plug engines.

cgfen

so if firing order = 1-6-2-4-3-5......
Do you;
find TDC firing #1 and test
rotate 120 degrees to #6 and test
rotate 120 degrees to #2 and test
..... through to # 5?

I guess I'm asking if;
more than one cylinder can be tested without rotation
or
does every 120 degrees rotation after #1 TDC = TDC firing on the "next" cylinder.

Thank you

Craig

Mike J

You are bang on -
Every 120 degrees clockwise on the engine moves to the next firing position. So just follow the firing order. You can double check your position by checking the rotor position on the cap - the rotor should be pointing to the cap wire that corresponds to the piston being tested.

Cheers

Mike

Mike J

Oh that also means you do two full rotations of the engine to test all cylinders (well technically 600 degrees since the last 120 degree rotation gets you back to the first position)

It also means u do not have to start at #1. U can start on any piston as long as its TDC on firing.

Cheers

Mike

IXLR8

I bought the Eastern Technology E2M Differential Cylinder Pressure Tester from Aircraft Spruce. You will also need to order the 14 mm adapter.

This model includes a built-in Master Orifice, for fast and easy instrument accuracy/verification.

IXLR8

The most accurate way of verifying the TDC mark on the pulley is by taking a dial reading before and after TDC (equal dial readings of course) and taking note of those positions on the pulley. TDC is exactly between the two positions.