Complete rebuild finding TDC

[Jmann8686]

Im in the process of rebuilding my 79. Had the cylinders bored to 700 and got the pistons installed and the cylinder on. I'm working on the head right now and lapping valves and getting the correct shims for my RD springs. (I found the right combo. Just have to go get three more sets) after I get that done I will be installing it. Obviously. My question is about TDC. Right now I have my pistons like this.



Is this correct.

Thanks

 

[TwoManyXS1Bs]

Looks like TDC to me.

Closely watching the pistons, relative to the edge of the bore, while slowly twiddling the crank back/forth will get you within a few degrees of TDC. And, that would be good enuff for installing and timing a non-adjustable cam (one that you trust).

If you're going to be dialing in an adjustable cam, best to use a degree wheel and piston stop, get precise TDC...

 

[Jmann8686]

Looks like TDC to me.

Closely watching the pistons, relative to the edge of the bore, while slowly twiddling the crank back/forth will get you within a few degrees of TDC. And, that would be good enuff for installing and timing a non-adjustable cam (one that you trust).

If you're going to be dialing in an adjustable cam, best to use a degree wheel and piston stop, get precise TDC...

Never heard of an adjustable cam until now. I have a shell 1 cam from Hoos racing.

 

[XSLeo]

If you have the stock rotor and stator, TDC is easy to find. Install both and see if the marks line up.
Leo

 

[grizld1]

Oh, they're all adjustable, jmann; with some you have to press the sprocket off, and some have sprockets with slots secured on bolts.

Guys, those procedures would be fine if you're working with a stock cam at stock deck height, but sadly, except for the ones from mrriggs' machinist, the Shell #1 grind cams on the market tend to be ground a bit sloppy. Shell published installation valve events as IO=25* BTDC/ IC=45*ABDC and EO=45* BBDC/EC=25* ATDC, but real world samples usually show the intake opening ground short for some reason. My first time around with the Shell #1 I tried spreading the error, and that didn't end well; wound up short shifting a lot. What's worked best for me is to bias the timing toward the exhaust opening, retarding the intake opening and letting the closing events fall where they may; I wind up closer to 20 * BTDC intake opening than to 25 (my cam, by the way, was bought from Shell, not his successors). As Gary Hoos has noted, the typical misgrind doesn't seem to hurt power. Anyway, I don't like to take anything for granted trying to dial in the Shell cam, even the 2* or so of error that's not unusual for the factory marks. Jmann, I'd recommend that you lightly secure the cylinders with a couple of spacers and nuts and set up a dial indicator on a piston crown. Take a degree reading at .050" drop on either side of TDC and set your mark in the middle.

 

[Jmann8686]

If you have the stock rotor and stator, TDC is easy to find. Install both and see if the marks line up.
Leo

Yeah I can dig it out and put it back on. I took it off cause im replacing it. But it has not been tossed yet.

 

[Jmann8686]

Oh, they're all adjustable, jmann; with some you have to press the sprocket off, and some have sprockets with slots secured on bolts.

Guys, those procedures would be fine if you're working with a stock cam at stock deck height, but sadly, except for the ones from mrriggs' machinist, the Shell #1 grind cams on the market tend to be ground a bit sloppy. Shell published installation valve events as IO=25* BTDC/ IC=45*ABDC and EO=45* BBDC/EC=25* ATDC, but real world samples usually show the intake opening ground short for some reason. My first time around with the Shell #1 I tried spreading the error, and that didn't end well; wound up short shifting a lot. What's worked best for me is to bias the timing toward the exhaust opening, retarding the intake opening and letting the closing events fall where they may; I wind up closer to 20 * BTDC intake opening than to 25 (my cam, by the way, was bought from Shell, not his successors). As Gary Hoos has noted, the typical misgrind doesn't seem to hurt power. Anyway, I don't like to take anything for granted trying to dial in the Shell cam, even the 2* or so of error that's not unusual for the factory marks. Jmann, I'd recommend that you lightly secure the cylinders with a couple of spacers and nuts and set up a dial indicator on a piston crown. Take a degree reading at .050" drop on either side of TDC and set your mark in the middle.

So I'm new to this whole complete engine rebuild. Are you say to leav to secure it as is and use the dial indicator. And mark tdc that's way. I will be using the power dynamo Ignition so should I put that on before I use the dial indicator.

 

[grizld1]

Just get the cylinders fastened down lightly so they don't jink around while you're turning the crank. You'll need to install the Powerdynamo to make your timing marks. Figure out how you're going to mount your degree wheel.

 

[Jmann8686]

Just get the cylinders fastened down lightly so they don't jink around while you're turning the crank. You'll need to install the Powerdynamo to make your timing marks. Figure out how you're going to mount your degree wheel.

Aweosme. Thank you.

 

[grizld1]

Hope you get lucky and don't need to move the sprocket, but if you do I'll walk you through it. Post your numbers when you have them.

 

[Jmann8686]

Hope you get lucky and don't need to move the sprocket, but if you do I'll walk you through it. Post your numbers when you have them.

Are you talking about the sprocket on the cam

 

[grizld1]

Yep.

 

[Jmann8686]

Yep.

Cool cool. Just double checking. I will get back when I have time to get back to working on the engine. Thanks again for the info.

 

[grizld1]

Mrriggs posted a fine thread on this topic; you might want to do a search and give it a read, there's good stuff there. You have a bit of leeway in setting cam timing, but you want to avoid getting the exhaust opening too far advanced.

 

[hooser]

Megacycle makes a cam sprocket that allows you to adjust the cam timing but you should not need it , the Shell I sent you will be very close. It is set at 23 degrees BTDC @.050 lift.
To find true TDC put your degree wheel on. with pistons at the top move your pointer to 0 , move the crank one way, read measurement when piston just moves , starts to go down. Go the other way, read measurement when piston just moves, TDC is the center between those numbers. If it is 20 one way and 10 the other way move you pointer 5 , then recheck until the numbers going left and right are the same, reset the pointer to 0 you now have TDC. leaving it there Now go to the clutch side and put a mark or I use a magic marker and mark one of the splines on the crank gear and make a mark on the bearing and case across from it. Now when you are installing the cam or ignition just make sure those marks line up and you know you are at TDC. If I can find the picture of where I make the mark I will post is or email you.

 

[grizld1]

Gary, you're the only guy I know who inspects these camshafts and dials them in before they go out the door. Great work!

 

[hooser]

Thanks, Shell told me to do it, I have the same set up for doing it as he had. it makes it easier for guys that do have the degree stuff, that way they just align the dot with the cylinder head.

 

[fredintoon]

Yeah I can dig it out and put it back on. I took it off cause im replacing it. But it has not been tossed yet.

Hi Jmann,
FWIW, put the stock system back on and leave it there. Or carefully save it for when you get sick & tired of trying to get the replacement to work right.

 

[Jmann8686]

Megacycle makes a cam sprocket that allows you to adjust the cam timing but you should not need it , the Shell I sent you will be very close. It is set at 23 degrees BTDC @.050 lift.
To find true TDC put your degree wheel on. with pistons at the top move your pointer to 0 , move the crank one way, read measurement when piston just moves , starts to go down. Go the other way, read measurement when piston just moves, TDC is the center between those numbers. If it is 20 one way and 10 the other way move you pointer 5 , then recheck until the numbers going left and right are the same, reset the pointer to 0 you now have TDC. leaving it there Now go to the clutch side and put a mark or I use a magic marker and mark one of the splines on the crank gear and make a mark on the bearing and case across from it. Now when you are installing the cam or ignition just make sure those marks line up and you know you are at TDC. If I can find the picture of where I make the mark I will post is or email you.

awesome. thank you. some pics would be great. I'm a very visual person.

 

[Jmann8686]

Hi Jmann,
FWIW, put the stock system back on and leave it there. Or carefully save it for when you get sick & tired of trying to get the replacement to work right.

Thanks. I will take that into consideration. But i'm going to give the new ignition a go. Gary at Hoos has been great and i'm going to take his word that the power dynamo is a good system. and I have yet to read or hear anything bad about it.