explenation on retiming the SC motor.

1990XR7SC

Registered User
Ok as the title states i need one of you guys who have rebuilt many of these motors to explane to me how to retime the motor. Ive had the marks on the crank and cam gear lined up then set the cam sensor up like in the pics and after it was all together it would backfire through the exhaust. so i tought it was out of time so i retimed it on compression stroke with intake valve and exhaust valve closed on #1. Got it together again and still backfire. But now i have been reading on here (link enclosed)

http://www.sccoa.com/forums/showthread.php?t=107752&highlight=timing+chain

Now this is where i found the timing marks had to be lined up but im confused on if it should be on compression stroke or not. Also can someone explane the cam timing in more detail than this

http://www.sccoa.com/forums/showthread.php?t=46483

Thanks ahead of time for your time.
 
Are you sure you have the plug wires from the coil pack to the correct hole?

The coil pack wires to cylinder are as follows

Back side of coil pack
passenger side 1 2 3 driver side
.....................5 6 4
Front side of coil pack

Cylinders numbered as follows
passenger side from front to back 1 2 3
driver side from front to back 4 5 6
 
ive checked the wires 3 times tracing them with a diagram i found when i serched. So thats 100% right. But the thing im asking is what stroke does the timing need to be on. TDC? BTDC? ATDC? what?ive been taught to put #1 at TDC then match up the timing marks but we all know SC motors are different than the NAs. And im still foggy on how the csm sincronizer is set/timed. Does it get done at TDC or before? the directions were a little hazy to me. Plus pics would help alot.
 
yeah the bhj i bought has one on it and when i had the crank timed with #1 at TDC the balencer lined up with the 26* mark. Also how would i check to make sure that bhj got the mark correct? i don't have my origional balencer. But like i said pics would help alolt.
 
Last edited:
ive checked the wires 3 times tracing them with a diagram i found when i serched. So thats 100% right.

I believe you. But I have to say I just went through a week of needless wrenching for that exact reason. I checked them 3 times. And somehow I got it wrong. If you know which bank is misfiring, it's easy to switch the wires at the coil pack into a different order just to make sure. There are only 6 possible combinations for each bank. ABC, ACB, BAC, BCA, CAB, CBA.

But anyway, about the cam synchronizer timing. That second thread you linked to has all the info you need. Just align it to look like the picture. And the cam should be at 26* ATDC on the compression stroke. As the thread says, the BHJ mark may not be at the same location as the stock balancer. Maybe it is at 0* and you need to make your own mark for 26*.
 
im unsure of what one is misfireing but i can heat it in the exhaust. I guess i just have to pull everything apart to check everything. Timing chain and the spark plug wires. but thanks for the info!
 
yeah the bhj i bought has one on it and when i had the crank timed with #1 at TDC the balencer lined up with the 26* mark. Also how would i check to make sure that bhj got the mark correct? i don't have my origional balencer. But like i said pics would help alolt.

BHJ doesn't have a mark for 26ATDC, it's mark is for 26BTDC. you need to use a piece of tape and transfer the 26BTDC mark to the other part of the balancer to get a 26ATDC mark. The second link you have above describes this process.
 
It's hard to goof up the cam to crank gear marks. point the crank dot up and the cam dot down with the chain on, then slide them on the cam and crank together.
cam-crankgears.jpg

For the balancer take a piece of masking tape and mark it from TDC to 26*BTDC then move the tape from TDC to the other side that would be ATDC and mark the balancer for 26*ATDC. Line the 26* ATDC up with the pointer on the front cover and set the cam syncronizer to look like the pic.
camsensor1.jpg
 
BHJ doesn't have a mark for 26ATDC, it's mark is for 26BTDC. you need to use a piece of tape and transfer the 26BTDC mark to the other part of the balancer to get a 26ATDC mark. The second link you have above describes this process.

So basically you take a 1.3" piece of tape and put it to the left side of the TDC marker on the BHJ correct, since the markings on the right side of the TDC are ATDC, correct or am I backwards?
 
im unsure of what one is misfireing but i can heat it in the exhaust. I guess i just have to pull everything apart to check everything. Timing chain and the spark plug wires. but thanks for the info!

Well, I'm just suggesting that you try swapping wires at the coil pack to save any extra work. Because you can do that and at least check it without tearing anything apart. Be sure to make any moves with the engine off so you don't get shocked, then start it up and see if it changes for better or worse.

Also, if you are unsure if the cam sensor is timed right, you can try unplugging it. It will run okay without it, although it may take several tries to start it. That could at least rule it out as the cause of the misfire.
 
So basically you take a 1.3" piece of tape and put it to the left side of the TDC marker on the BHJ correct, since the markings on the right side of the TDC are ATDC, correct or am I backwards?

Put a piece of tape on the balancer overlapping the TDC mark slightly and long enough to cover the 26 degree BTDC line. Then use a pencil or pen to transfer the marks on the balancer to the piece of tape, making note of the TDC mark and the 26 BTDC mark. The crank rotates clockwise, which means anything to the right of the TDC mark (when facing the balancer) is BEFORE top dead center, anything to the left is After Top Dead Center.

Once you have the tape marked, remove it and flip it over, lining up the TDC mark on the tap with the line on the balancer. Place it down, and transfer the timing marks on the tape to the balancer. Remove the tape and make more permanent marks on the balancer if you wish with an awl to scratch marks into it.
 
if memory serves me right it's only marked to 15 or 20. your tape has to be longer to add the extra graduated marks in hich you have to add yourself. i just copied the extra ones from the bal. and added them after the ones already on the tape i had previously marked.
 
if memory serves me right it's only marked to 15 or 20. your tape has to be longer to add the extra graduated marks in hich you have to add yourself. i just copied the extra ones from the bal. and added them after the ones already on the tape i had previously marked.

That sounds right. I think what I did was get the full length of the existing marks and move the tape over to the After top dead center area. Then take another piece of tape and make marks out to 15. Then move that new piece of tape over to the old one, lining it up so that it gave me 10 more marks. Then found 26 from there and made a groove with an awl to be the 26degr after top dead center mark.
 
Back
Top