Thunderbolt iv timing

[MikDee]

A few yrs ago, I put a new mild hydraulic cam from Summit in my stepson's 79' Camaro 350. Thinking I knew full well how to do this, showing off for my stepson, I put the timing marks on both gears on top of each other like this : and then put the Dizzy in lined up to #1,,, Well, when we went to start it, I had a hard time, and a Backfire, then an Engine Fire! Of course no hose nearby This threw me for a LOOP! But, I knew immediately what was wrong, so next I took out the Dizzy, gave it 1/2 a turn, and the car started up, and ran perfectly! It had a nice mild lope as well

Believe me, my mind was blown by this, and I vowed never to forget this lesson!

 

[MikDee]

It doesn't matter which cylinder it's lined up for, as long as the marks align. As long as they line up the engine is correctly (valve) timed.... If you don't like the marks where they are, turn the engine one crankshaft revolution and they will be lined up again, but the mark on the cam sprocket will be at the top.... The valve timing will have not changed.

I beg to differ! With the cam mark at 12 o'clock, the engine is set to fire on #1, With the cam mark at 6 o'clock, the engine is set to fire on #6.
It's a 4-cycle engine, I turn of the crank, is 1/2 turn of the Cam- hence #1, the next turn of the crank, is 1/2 turn of the Cam- hence #6
Some of the literature online, and in manuals is wrong! "And that's all she wrote!" Quote Baretta!

 

[achris]

The engine we are working on here is already running, we are just verifying that the cam timing is right... And to verify it, it doesn't matter, marks up, marks down.... They are the same.... Also, and this is an important point, so listen closely. 1979 350 Car engine.... 1993 454 Marine engine.... They are both GM, but that is where the similarity ends... I will hear no more on this subject, please. It isn't helping the OP.... To the OP, I'm terribly sorry for this distraction.. Where are you with your engine? Have you managed to check the Balancer positioning yet? Cheers....

 

[Bt Doctur]

The marks HAVE NOTHING TO DO WITH TIMING AN ENGINE . those marks are there to correctly time the CAM to the CRANK. nothing more.

 

[MikDee]

To achris, Bt Doctur, NH guy, & klawton55, I'm sorry to have taken this thread off-topic. It's true that it doesn't pertain here with the O.P. having a running engine to begin with. As far as valve timing, from my latest experience, I have my own opinion. Just take it with a grain of salt, and find out what works best for you. I guess I was acting like a real REAR admiral!,,, lol Peace brothers!

 

[NHGuy]

Believe it or not, that just clarified a lot for me. Good luck with it OP

 

[klawton55]

achris- I did check the harmonic balancer and it was fine. Even purchased new one just to compare the markings. What else can I check?

 

[Bt Doctur]

Well, if the cam is timed correctly then your on the wrong spark plug wire. facing the engine on your right starting from the front of the engine,
1,3,5,7 . on your left starting from the front of the engine 2,4,6,8
One other reason is the cam. Was the cam replaced? with what type? lift/duration.
A somewhat wild cam might account for the lumpiness and needs an idle around 1500

 

[NHGuy]

So, you have the cam timed right, did you go back and confirm top dead center? How, with a piston stop? Then did you puff test it to confirm #1 was at TDC when the rotor was facing the #1 plug wire contact in the cap? If you did not you could be testing it with the distributor off by 180 degrees. Did you notice those guys put me in my place about the timing dots on the cam and crank sprockets? When the cam dot is at 6 oclock and the crank dot is at 12 that's the #6 firing position. If you stabbed the distributor to #1 with the motor at the install position you will need to 180 the distributor to get things right. Then TDC will be at #1.
You can also confirm TDC at #1 by watching the valves. As the crank comes toward TDC the #1 exhaust valve will already be closed and the #1 intake valve will become closed. This happens every other revolution of the crank.

 

[klawton55]

NHGuy- I turned the motor over until I felt it puff out of number one cylinder, then I installed distributor. achris- I am using the correct cylinder for the timing light. I did install a new camshaft it was supposed to be a stock replacement, Camshaft - replaces OE cam #3883986. I am going to pull of the rocker covers tomorrow and inspect the rockers I probably will pull the intake as well to look at the lifters and camshaft. D you think I could have wiped out the cam already? I may have to try and find my old cam and install it. You mentioned that if the cam was bigger I might have to have the idle up higher. Would it hurt if I raised the rpm and tried to set the distributor? Would the 8 degrees still apply. Just thinking here.

 

[Fun Times]

I have a 92 454 with thunderbolt iv ignition. I have recently had the block bored and all new internals.

Just a thought while reading all of this. Did you install a new camshaft? and/or crankshaft? If so, Would you happen to know if your engine assembler used a camshaft degree wheel to synchronizing the camshaft's position with the crankshaft?

Here's some info about degreeing a camshaft if interested.
http://www.cranecams.com/bulletins_listview.php?s_id=5

Also the difference between cam timing & ignition timing if interested.
http://www.badasscars.com/index.cfm/...rod/prd370.htm

 

[achris]

If the cam is stock and everything else seems to be ok, I would start looking at triple checking you have the plug leads right, that they are the right spark plugs, you have the leads in the dissy cap right. Are you using an advance timing light or just a standard one? If it's an advanced, then make sure you have the setting right.

As for running it at higher engine speed to set the timing... Can't.. The ignition module uses the engine speed to calculate the advance. Once the engine is above idle, advance is applied. You could use the timing curve to calculate what the advance should be and set it there. That should get you close enough to be able to get the engine speed down and then set the timing at 8BTDC at idle.... Check which module you have (should be stamped on the Thunderbolt IV module with 'V8-xx' That 'xx' is the total advance of the module. Use that with the chart in service bulletin 95-11 and find the curve for your engine. http://www.boatfix.com/merc/bullet/95/95_11.PDF This is the bulletin with all the curves.

 

[klawton55]

I installed a new crank and cam, everything is new besides the rockers and push rods, and no the crank and cam were not synchronized. The engine builder bored it and installed new cam bearings but then I installed everything else. Thanks for the links I will check them out.

 

[klawton55]

The firing order is 1, 8, 4, 3, 6, 5, 7, 2 correct?

 

[achris]

The firing order is 1, 8, 4, 3, 6, 5, 7, 2 correct?

WHAT!?!?!? You're using THAT firing order.... Yes, that is correct (if the cam is genuine stock...)....

 

[klawton55]

Haha. You know I was really hoping you would say no its this and it would be that simple.

 

[klawton55]

Is it different if its not stock?

 

[MikDee]

Is it different if its not stock?

No, the firing order would always be the same. It appears you have the cam timing, & ignition timing set right or the engine would never run that good!

I would move on to checking your valve adjustment, if the valves are too tight, it would run rough, and not want to idle, if the valves are too loose, it would backfire, if both things are happening then chances are your valves are out of adjustment. This maybe your whole issue?

 

[klawton55]

That makes sense. But I am unsure how to adjust the valves. The engine is a gen v, aluminum valve covers and has bolts holding the rockers on. They just get torqued, correct? I will check them tomorrow to ensure they are all secure. If there is something that I am missing I am all ears, I am dying to get on the water!

 

[achris]

Mik...:facepalm: Please READ THE BOOK, there is no, repeat NO, valve adjustment on the Gen V engines, just button them up, torque the rocker bolts to 45lb-ft and THAT IS IT!

Also, on firing order. The cam has quite an effect on firing order. Yes, the pistons will continue to go up and down in the same order, but remember there is always 2 pistons at TDC at a time. One will be firing (compression/power stroke) and the other will be 'on the rock'. It's the positions of the cams on the camshaft that will determine which stroke that cylinder is on, hence the firing order. A very good example is the Ford 302 engine. Standard factory firing order and the firing order of the Mercruiser '888' is different... Why? Because the 888 uses the Ford 351 cam, not the standard 302 cam....

K55, try this. It's a longshot, but I think you're there now. With the engine running as best you can get it, remove the spark plug leads one by one. You should be able to notice a drop in revs when each lead is lifted. Albeit a small drop with a big V8, but you should be able to hear it. If any cylinder doesn't drop, it's a problem. If you have 2 cylinders that don't drop, check their positions in the firing order. If they are opposite each other (opposites would be 1 & 6, 8 & 5, 4 & 7, 3 & 2)... Try swapping just those 2 cylinder spark plugs and see if that's any better.... I guess you see where I'm looking here....

Chris....