Finding TDC for all cylinders

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dixon5553
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Location: Novi, Michigan

Finding TDC for all cylinders

Post by dixon5553 »

On a LM engine, I know how to find TDC on cylinder one, I want to confirm the process to use to find TDC on the remaining 5 cylinders. Is it as simple as manually turning the engine over until the dist. rotor lines-up with the next terminal on the dist cap? Somehow I don't think so. And standing from the rear of the car, you turn the engine counter-clockwise, is this correct? As always that for the help.
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flat6_musik
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Re: Finding TDC for all cylinders

Post by flat6_musik »

I'm thinking that it IS that simple, but that wouldn't actually be super-accurate. You would turn the motor over, yes, counter-clockwise (from the rear bumper) and every 120 degrees (1/3 of a crank turn) would be another TDC in the firing order. I hope I'm right on this! :rolling:

You could buy yourself a degree wheel to attach to the crank......if space permitted....

Image
1949chevy
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Re: Finding TDC for all cylinders

Post by 1949chevy »

I think another way to find TDC ( and I do not know why you would) on other cylinders would be to view the intake valve on that cylinder (valve covers removed)...when it opens then closes and that piston comes to the very top...that cylinder would be on tdc. The first one would be #1 and check the harmonic bal and make sure the marks line up...then follow the firing order as I stated above would be the most efficient way. I would remove the plugs so the engine turns over easy and when #1 is tdc take a wood rod (1/4 inch would be good..a wooden dowel) and measure and mark the rod when on top of the piston when tdc is achieved and compare to the other cylinders.
martyscarr
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Location: Eugene, OR

Re: Finding TDC for all cylinders

Post by martyscarr »

Here's a picture of a Corvair degree wheel, you can download the pdf and print, then glue it to your crank pulley to find TDC for all cylinders. I glued my paper copy to a piece of magnetic sign material and stick it on when needed.
Image

Download is here: http://www.n56ml.com/corvair/degree_wheel.pdf
Thanks to Mark Langford for that - BTW there are lots of good pics on Corvair engine building on his site, take a look.

1949Chevy asks: I think another way to find TDC ( and I do not know why you would)...

I would guess he is doing a leak down test and needs to have each cylinder at TDC.

Marty Scarr
dixon5553
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Location: Novi, Michigan

Re: Finding TDC for all cylinders

Post by dixon5553 »

Thank for the link to the degree wheel, this was helpful. Still having a problem finding TDC for remaining cylinders. When at TCD#1 rotor at #1 terminal ok, then I go 120 degrees counter clock wise and it should be TDC # 4, yet when I check the rotor, it's not on #4 terminal on the dist cap. Same thing when i go 240 degrees past #1 to get TDC for #5, the rotors not on terminal # 5 - what am I missing here? Thanks.
64powerglide
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Re: Finding TDC for all cylinders

Post by 64powerglide »

Did you do # 1 on a timing light & set it at zero running???????
64Powerglide, Jeff Phillips

Kalamazoo, Mi..
dixon5553
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Location: Novi, Michigan

Re: Finding TDC for all cylinders

Post by dixon5553 »

No Jeff, I did not do this.
64powerglide
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Re: Finding TDC for all cylinders

Post by 64powerglide »

I think , but i'm not sure that you would have to turn the dist. to zero on the pulley "degree wheel" when you start with # 1. Any other thought's on this theory???????
64Powerglide, Jeff Phillips

Kalamazoo, Mi..
martyscarr
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Location: Eugene, OR

Re: Finding TDC for all cylinders

Post by martyscarr »

dixon5553 wrote:Thank for the link to the degree wheel, this was helpful. Still having a problem finding TDC for remaining cylinders. When at TCD#1 rotor at #1 terminal ok, then I go 120 degrees counter clock wise and it should be TDC # 4, yet when I check the rotor, it's not on #4 terminal on the dist cap. Same thing when i go 240 degrees past #1 to get TDC for #5, the rotors not on terminal # 5 - what am I missing here? Thanks.
So where does the rotor point when you turn the engine CCW 120 degrees? Or when you turn it 240 degrees, where does it point?

When you start at TDC on #1 cylinder, and you turn the engine 120 degrees CCW, the rotor should turn to the next terminal, which is 60 degrees rotation clockwise. Is that what is happening?

Marty Scarr
64powerglide
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Re: Finding TDC for all cylinders

Post by 64powerglide »

64powerglide wrote:I think , but i'm not sure that you would have to turn the dist. to zero on the pulley "degree wheel" when you start with # 1. Any other thought's on this theory???????
Guess I should have said you need to line up #1 on the dist. cap & with the rotor when the pulley is on zero "TDC" then you should have compression every 60 degrees. 145236. Just as you first thought!! I THINK! :banghead:
64Powerglide, Jeff Phillips

Kalamazoo, Mi..
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Nickshu
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Re: Finding TDC for all cylinders

Post by Nickshu »

I found that during a leakdown test finding exact TDC where the air pressure would not blow the piston one way or the other was quite difficult and very fiddly.
Nick
1964 Monza Spyder Convertible #435 - Rotisserie restored - SOLD ON BRING A TRAILER 4/30/2019 - Check out my restoration thread here: [corvaircenter.com]
Thanks to all the awesome CCF, CF, COG, and CORSA members who helped me with the restoration!
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Iceland Spyder
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Re: Finding TDC for all cylinders

Post by Iceland Spyder »

Hi, one rotation is 360 degrees divided by 6 is 60 degrees between compression. So#1 tdc and #4 60 degrees ccw #5 another 60 degrees and so on. Hope it makes cense to you. Have a nice one. Stefan. 64 Spyder coupe.
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