Trying to get 30* TDC for a boost leak test help

[spadepro22]

So to get TDC I need to turn the motor by hand CLOCKWISE. So to make sure Im going clockwise, I pull down on the ratchet right? And once I get it to TDC how much of a turn is 30*

 

[WizardTSi]

Clockwise, if the ratchet is straight down, you want it to go left.

 

[spadepro22]

Ok, now I have tdc, know how far to turn to get 30* rotation?

 

[WizardTSi]

There should be timing marks on the timing belt cover. I cant remember if it goes to 10° or 15°. Use it as a guide to guesstimate 30°. Maybe a quarter turn, or a little more

 

[spadepro22]

I checked the mark on the lower timing cover and its 5* at TDC. Will a quater turn put me at 30*?

 

[Colt4G63 also]

I've done several dozen BLTs and I guess I've always just been lucky, because I have never had to turn the engine to get it to hold pressure. Sometimes it turns itself a little, but I've never had all the air start blowing out the exhaust pipe or anything.

 

[spadepro22]

I've done several dozen BLTs and I guess I've always just been lucky, because I have never had to turn the engine to get it to hold pressure. Sometimes it turns itself a little, but I've never had all the air start blowing out the exhaust pipe or anything.

This will be my 1st time. Is there a way to mess up the vavles if the degrees is not right or will it just leak out the exhaust?

 

[DSM1G90]

Well TDC is at the 12:00 position, +90* is at the 3:00 position, +45* is 90* cut in half.

Now cut 45* in half and add 7.5* to 22.5* get your 30*.

Think of a pie chart and do the elementary geometry.

 

[spadepro22]

Well TDC is at the 12:00 position, +90* is at the 3:00 position, +45* is 90* cut in half.

Now cut 45* in half and add 7.5* to 22.5* get your 30*.

Think of a pie chart and do the elementary geometry.

Thanks for the crash course, so to sum this up, its a little less than a quarter turn?

 

[My1GLaser]

There are 360 degrees in one full engine revolution and you want to turn it 30 degrees.

30*/360*= 1/12th of a turn

For reference: 1/4 of a turn is 3/12th of one revolution, so you need a lot less than 1/4 turn. Literally you need to turn it 1/3 of 1/4 of a turn, but that might sound confusing.

 

[Colt4G63 also]

There's no way putting compressed air into the intake will mess up the valves. You're making too much out of it. I did two boost leak tests at work just last Friday.

 

[spadepro22]

There are 360 degrees in one full engine revolution and you want to turn it 30 degrees.

30*/360*= 1/12th of a turn

For reference: 1/4 of a turn is 3/12th of one revolution, so you need a lot less than 1/4 turn. Literally you need to turn it 1/3 of 1/4 of a turn, but that might sound confusing.

So if TDC is at 12:00 and 90* is at 3, I should turn it to about 2:00? Funny how it is turning into a math class, but it should clear it up for the people that didn't have a clue like me.

There's no way putting compressed air into the intake will mess up the valves. You're making too much out of it. I did two boost leak tests at work just last Friday.

Not making too much out of it, just want to be sure. Can't learn if you don't ask.

 

[My1GLaser]

No. Using that scenario, you should turn it to 1:00.

12 hrs in a clock, 1/12th of a turn is 1 hr!

You still need the same fraction of a circle to get to 30* whether your talking hours on a clock or degrees of crank rotation. 1/12 is the same fraction as 30/360, its just reduced to the lowest terms. Get an analog clock and see how much of a turn 1 hour takes up on the clock face and go turn your crank that much!

I never really have that much problem on 272s with overlap during a BLT and I doubt my crank lands in the exact best spot every time I do one. I have had to turn it by hand before because of where the motor stopped, though. Get your engine to operating temp so the rings are expanded. I always make sure its at operating temp when I do a BLT or compression test!