Mike J

I have a few different ones, but the one I mainly use now is this Snap-On one:



and use a Snap-On compression guage as well:



Cheers,

Mike

Mike J

Yeah, critical for timing, but I think being out a few degrees on a leak-down does not matter - the valves remain closed for some time on either side of TDC anyways (depending on the cam of course). If it's too far out the air will push the cylinder though, which is surprising if you are not ready. I found the marks on the main crankshaft pulley to be pretty accurate, definitely accurate enough for the testing. This is over several cars....

Cheers,

Mike

IXLR8

It won't in this case, but I stated "the most accurate way of verifying the TDC mark on the pulley" because I started seeing links to dial indicators and tools to find TDC on this thread.

I wonder if the Snap-On set uses the standard 0.040 orifice.

BesideTheBox

Alex, Mike,
Thank you for the recommendations guys. I bought an inexpensive OTC 5609 Cylinder Leakage Tester Kit five or six months ago.
It has dual gauges similar to the Snap-On and Eastern Technologies units.
I used the distributor to find the top of the firing order and then used the marks on the crankshaft pulley for TDC for each cylinder.

cgfen

Mike, thanks for taking the time to reply.
Appreciate your help.

Craig

phoneyman

Probably a stupid question, but how do you manually rotate the motor? My dad and I were trying to think this through and couldnt figure it out. We tried turning the rear wheels while in gear but that didnt work. I was thinking maybe you can turn the fan pulley nut with a socket but I figured that might not be the right solution...

Mike J

First thing, take out at least one plug per cylinder - it makes it much easier to turn over

Second, turn the engine clockwise only looking at the fan.

Third, you can use the large nut on the fan/alternator shaft to turn the engine over with the car in netural. If the belt slips, then push on the side of the belt to add tension so it grips - that is the way I have always done it and it seems to work fine.

Cheers,

Mike

phoneyman

I'll give the fan alt nut another try. The first time it spun pretty freely but the fan didn't move. Didn't want to break the grip of the nut against the bearings and end up with alternator problems, like stripping, that I've read on here.

cgfen

sage advice.
I just did leak down test and removed all 6 prior to rotating.

I've also seen a few threads on Pelican where posters say to ensure you remove the "big wrench" from the nut prior to charging the system with compressed air......
ouch, that must have been a hard-learned lesson.

Craig

race911

Do enough of them, and most certainly you've been there. Guess it's more critical with the race cams of yesteryear where TDC alignment spot on is recommended.

You can probably be ~5 degrees off on a street engine before filling the cylinder with compressed air will move a piston, and therefore the crankshaft and ultimately the fan.

Mike J

Totally agree with Ken - its rare if you are lined up with the marker on the crankshaft pulley that indicates TDC on the selected piston that the compressed air will kick the piston down. I have had it happen once in that last several years, and it only moved the crank 10-15 degrees before stopping. I do take the wrench off the pulley nut on each turn anyways, and check that it remained at TDC when proceeding to the next cylinder...

Cheers,

Mike

race911

And to clarify my comment on "race cams", it's all about being more TDC critical with the high overlap. Nothing like rolling the crank over to whatever cylinder you're testing, pressurizing, and finding 20-30-50% leakage........ Steve W or someone can correct me, but I think it was the original 906 sprint cam that had the intake open measurably at TDC.