Thunderbolt iv timing

[achris]

Did you check the balancer like I suggested? If the rubber of the hub has slipped (and it does happen) then what you see on the timing marks will not be even remotely accurate...

 

[klawton55]

I did not. I was not confident of the timing marks. Also if I dropped the idle to 700-600 it would also start to backfire. I will check that tomorrow. Thanks

 

[MikDee]

Have you done a valve adjustment lately? If your valves are adjusted too tight it won't idle right, check that out. I like to do it while running, but it can get a bit messy. Once the engine is warm, and idling, I loosen one up at a time just till I hear a slight tick, then slowly tighten it down till it's quiet, then go another 1/4 of a turn, twice, slowly, to a total of 1/2 a turn down. Then move onto the next one, till they're all done.

 

[klawton55]

It has hydraulic lifters.

 

[achris]

If the engine is a Mark IV, then you do need to adjust the valves, as per^^, but it's 1 turn down, not 1/2... If the engine is a Gen V, then just torque the rocker bolts to 45lb-ft... Not sure if it's a Mark IV and a Gen V? Stamped steel rocker covers=Mark IV... Ali rocker covers=Gen V

 

[MikDee]

It has hydraulic lifters.

And? They don't adjust themselves! Who adjusted them after the engine was built?
By the way, I know the specs say 1 turn down, but I find the engine is more "lively" at 1/2 a turn down, besides you just want them tight enough that they don't come loose, and clatter.

 

[bruceb58]

Have you double checked that you replaced the spark plug wires in the correct firing order? I have done this and it's amazing how well a V8 can run with a couple wires crossed.

 

[MikDee]

Have you double checked that you replaced the spark plug wires in the correct firing order? I have done this and it's amazing how well a V8 can run with a couple wires crossed.

Been There, Done That! Myself

 

[klawton55]

The engine code came out to a gen v. But not sure if the heads were used from the original motor, since the boat is an '89. The only time that I have adjusted valves the rocker had a screw that you could turn with a lock nut. How would I go about adjusting them? I realize that you say 1 turn or half a turn. But on what? Sorry for my ignorance.

 

[MikDee]

The engine code came out to a gen v. But not sure if the heads were used from the original motor, since the boat is an '89. The only time that I have adjusted valves the rocker had a screw that you could turn with a lock nut. How would I go about adjusting them? I realize that you say 1 turn or half a turn. But on what? Sorry for my ignorance.

This is a lot simpler on a Chevy motor, just loosen, or tighten the rocker arm nut to suit! They are like lock nuts, but adjustable ones. On old engines, they get worn, and start to get loose, then need new replacement nuts, but I've never had to replace them yet, after redoing many Chevy engines.

 

[klawton55]

The rockers had a bolt no nut, so I would assume no adjustment. I did check the wires had two crossed but that was before it even started. I believe they are good but will check again.

 

[MikDee]

If the engine is a Mark IV, then you do need to adjust the valves, as per^^, but it's 1 turn down, not 1/2... If the engine is a Gen V, then just torque the rocker bolts to 45lb-ft... Not sure if it's a Mark IV and a Gen V? Stamped steel rocker covers=Mark IV... Ali rocker covers=Gen V

I guess it's a Gen V engine? As achris has mentioned. Sorry, don't know the proper procedure for adjusting these valves then?

 

[achris]

I guess it's a Gen V engine? As achris has mentioned. Sorry, don't know the proper procedure for adjusting these valves then?

It's in what you quoted.... :facepalm:

 

[NHGuy]

Mik, I've been reading your posts with interest because in manual #15 for the 1988 year 305,350 and 454 it says to line up the dots bottom to top and thats TDC on #1.
What's even more interesting is that I just put a cam in my motor this spring and lined em up that way. It started fine.
When I was starting it for the first time I didn't realize I had a weak battery and called the Comp Cams help line to talk over TDC. One of their guys said the same thing you are saying. Perhaps the car motors are different. I don't understand how though, boat motors are supposedly crate jobs.
​I don't want to hijack, but the OP appears to have it right. To verify go to manual 16 in the boat info site and go to image page 89 which is section 3 page 55 of manual 16.

So OP, you had the marks right. The point of the cam gear aligns to the indent of the crank gear when the dots are directly in line. To confirm further, the cam gear guide pin will be at 3 oclock too.

It should run there and show you real ignition timing unless I'm wrong, in which case smarter folks will tell us!

When you go to start it have an adjusting tool ready for the idle screw, it could be up too high and the motor might rev up.
Good luck, and let us know how it goes.

 

[Bt Doctur]

mechanically theres nothing different , but you should not even be mentioning TDC with timing chain installs. Dosent matter,what matters is lining up the dots.

where a piston is makes no difference because your not timing it yet.

 

[Bt Doctur]

 

[MikDee]

No Title

That's to line up TDC for Cylinder #6 to fire! Both gear marks need to be at 12o'clock position to fire on Cylinder #1

 

[MikDee]

No Title

That pic is wrong, that's not for Cyl #1, it's for Cyl #6! This sketch is right!

 

[Bt Doctur]

No, that's to line up the cam with the crank, nothing more. The dots have nothing to do with the pistons. TDC is established with a piston stop tool and the harmoninc balancer is checked against that for a true zero indication .Once the heads are on you set the motor to TDC #1 compression and install the dist.

 

[achris]

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.