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Author Topic: first time cam degree ing...  (Read 15619 times)
Big Block
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Posts: 2348

Location: Amish Wonderland of Central Pa.

« Reply #45 on: March 11, 2018, 08:28:23 am »

You need to hit the stop in both the CW and CCW directions in order to compute True TDC.  Both are mentioned above.

Here is a step by step example with numbers:

1.  Rough eyeball TDC before adding stop.
2.  Move degree wheel/pointer to zero and lock down on balancer.

3.  Rotate crank roughly 20* CW and install stop, making sure the bolt just touches the top of the piston.
4.  Rotate crank 300+* CW (Yes CW again) until you hit the stop.  Lets say it stops at 338*.  This is your first real measurement so write it down.  
5.  Next rotate crank CCW until it hits the stop.  Lets say that it now reads 16*.  Write it down as your 2nd measurement location.  From these two values you can now calculate True TDC.
6.  First subtract 338 from 360 (TDC= 0/360), which gives you 22*.  This gives you the value from TDC that you found when going CW.
7.  Add that value to the value that you found when going CCW.  22+16=38.  
8.  Now take the 38 that you just computed and divide by 2, which gives 19.  
9.  Subtract that from the value that you found when rotating CCW.  16 -19 =-3.  Since it is a neqative #, you will need to subtract that 3 from 360.  That will equate to 357* on your degree wheel.
10.  357* is where True TDC is currently found on your degree wheel.  At that point the piston will be at its highest point in the bore.

11.  Remove stop and rotate crank to 357*.  
12.  Carefully loosen degree wheel from crank and rotate the wheel to "0" and lock it down.  You now have the motor and degree wheel both aligned to TDC.

Truth be told, you can also use your dial indicator method to find TDC if you want to and work with that.  It will not be as accurate as to what I am trying to portray to you, but unless you are using an infinitely adjustable timing set like this (which lets you set the cam timing up perfectly):  


Specifically note the slots (under the 6 bolts) that allow adjustment on the upper cam gear.  
If you are using the simpler multi key version without the slots, you will at least be in the ball park.



65' Stang, 434W NA, Victor Heads, Super Vic Intake, 11:1, Braswell Carb, Bullet SR Cam, G101A 4-Speed, 4:56 rear, 93 Octane Pump Gas  9.82@138.00
Big Block
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Posts: 2466

Location: Knoxville, TN.

« Reply #46 on: March 11, 2018, 10:07:06 am »

Well said Dennis, and I know it's much harder to describe the process, than to do it. I found TDC my first time in 1980 with my first Cleveland engine. A friend helped me and he was about 31 and had only built two engines before.

Back then we didn't have all the amazing aftermarket parts. Learning everything about balancing and blue printing an engine was a big factor to gaining any decent power over stock. Back then a 351 making 450hp was very very special. Now it's easy and 500-600hp is not a big deal.

To jetski247, don't become too worried about absolute perfect cam timing. The normal timing chains should get it within 2-3 degrees of where the timing design is made for(machining tolerances of the cam). So those decent timing sets costing $50 or so are very good choices, unless you have to have the last hp possible(the cam is custom made for that combo and needs to be perfect). The high end timing sets to get it closer to perfect, they cost a lot more. So decide based on your combination and how near maximum power you want it to get for the budget, select the timing set that makes the most sense. A $6k engine should have a very good timing set, a $1k engine shouldn't need it.


1991 Mark VII LSC Special Edition, soon to be OBDII and 4R70W, then GTC body kit and 347.
1998 Mountaineer, plans for A4WD and KB 2200 blower later, XP8 parts, paint and a 332.
1973 Ranchero and 72 Sport front end ...will be a 351 Clevor, EFI and 4R70W.
6 Banger
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Posts: 78

Location: bryan, tx

« Reply #47 on: March 11, 2018, 11:42:09 pm »

well said and thank you very much.

i understand this engine is a dot to dot engine but would like to practice while i have it on the stand. not really looking for any hidden hp...(stock engine lol) but would like to grasp the concept. the engine that is coming out will be a full stroker rebuild for sure

thanks again Dennis and CDW. those are the answer's i was looking for. and im assuming the computer will correct for not near perfect timing and wear and tear so the need to find true tdc or even counter adjust for future wear is not really needed in a computer controlled engine.??? i guess?

learning a new way to find tdc is for sure a......lol......... learning curve
all these years using a dial indicator to find tdc and i see all these piston stop stuff.....and im like wtf?

it was hard to grasp at first, i was like, who in the hell would use a piston stop to know where tdc is? i was always taught to watch the dial indicator when its stops and just starts to turn the other way after removing any slop and spin the engine over a few times first. that is how i always built any and all engines where i really really needed to know tdc like a rotary valve two stroke which even then gives you a 10 degree allowance or range.

but building 1.6L 450hp inline three cylinders.......everything and i mean everything has to be right on the money and tripple checked.......and ive always used a dial indicator but those are way way different engines. i would have never even known about a piston stop.....its always been dial indicator.

anyway, if time allows, im going to "try and degree" this stock cam on number one and see what variance of a grind i got, more less for knowledge than anything, and if i ever get to the day i build some romping 500+ hp stroker, i'll know what im going.

thanks again guys, i'll post up pics of what i got in a few days, kids are off for spring break and im off of work to spend with them, if i get a chance i'll be posting back with a whole bunch of " what do you do when this happens" kind of questions. for the mean time, engine is wrapped up at work stuffed in the corner until i return.


I'll take a 2 stroke over 4 any day......
it aint an engine unless it requires a mix drink to run

Man is smart............People are stupid.....
Leroy Bienek
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