1984 5.7L thunderbolt 4 timing chain question

[NHGuy]

Re: 1984 5.7L thunderbolt 4 timing chain question

View attachment Vacuum testing.pdf

 

[tfret]

Re: 1984 5.7L thunderbolt 4 timing chain question

NHguy this is informative info. I have not noticed any preignition pinking, although its really hard to hear with thru hull exhaust. I have done extensive vacuum leak testing. The only thing I ever found was a loose hose from the carb to the choke pull off diaphram which I replaced. I bought a vacuum gauge and did a lot of testing and the info also suggested late valve timing. I think I can get the tools and test the degree of the cam. I just don't have anything to compare it to to know if it's right or wrong.

 

[Scott Danforth]

Re: 1984 5.7L thunderbolt 4 timing chain question

Here is all I could find a while back on the stock GM 260hp marine engines from the mid 80's

202? duration intake
214? duration exhaust
395" lift intake
404" lift exhaust
112? lobe separation.

however there is not enough information to verify such as at what degree the cam lobe starts to lift, and what degree you would be hitting the 0.050" lift mark.

in lieu of the actual cam card you may just have to pull the damper, water pump and then the front cover.

 

[tfret]

Re: 1984 5.7L thunderbolt 4 timing chain question

Scott, thanks for the info. That's more than I had before. Like you said though, I still don't know when exactly the valves are supposed to open and close. I was trying to confirm that the cam is indeed timed wrong before pulling damper, pump, and timing cover. Naturally I don't want to spend all that energy if unnessesary.

 

[bruceb58]

Re: 1984 5.7L thunderbolt 4 timing chain question

Have you made sure you have full timing advance at 3500RPM? NHGuy has already mentioned this but didn't hear anything from you that you confirmed it.

You need an advance timing light or timing tape to measure this.

I really doubt its your timing chain. Marine engines just don't get used enough for them to wear out typically.

 

[tfret]

Re: 1984 5.7L thunderbolt 4 timing chain question

I have the advance curve printed out and in my timing light box for the next trip to the lake. I have not done this yet. I suppose the TB IV could be failing me. But my experience with power electronics like this is that they typically either work or not. Still it's possible that it's not providing the proper advance and certainly easy enough to check. Now I just have a plain old point-n-shoot timing light. Will that not work? Don't I just add the base time to the advance curve numbers to get the total time that I should see on the balancer mark? Or in this case I guess I need to put a timing tape all the way around the ballancer. Is this right or do I require something else?

 

[Scott Danforth]

Re: 1984 5.7L thunderbolt 4 timing chain question

measure your damper, buy a timing tape for the correct diameter damper. use your point and shoot to measure.

VP puts on timing tape from the factory, at least my vintage they did.

 

[bruceb58]

Re: 1984 5.7L thunderbolt 4 timing chain question

The timing tab isn't that big. The mark will be beyond the timing tab. You need something like this:
JEGS Performance Products 40703 Timing Tape : Amazon.com : Automotive

Just make sure you buy the tape for the correct diameter damper.

You can also just measure out 30? and make a mark and see where you are relative to it

 

[NHGuy]

Re: 1984 5.7L thunderbolt 4 timing chain question

Someone said this already but when you have the timing cover off and are at TDC you want the dot on the cam sprocket right above the one on the crankshaft gear.
Seems to me I read somewhere that the hot rod guys would actually retard the cam in old cars for power. So if your cam is timed late I'd be surprised, maybe if it's advanced you motor would feel weak.
I'd stay exactly stock with the cam timing, there are too many places you could go wrong changing cam timing.

I put on a timing chain this winter when I had my motor out for a reseal. I just got a Chevy truck chain from Rockauto or Summit or something. I think it cost $18. My 25 year old motor had maybe 5/8" deflection on the old chain, the new one is maybe 1/8" or 1/4" tighter, but I was in there and it was cheap and easy, so I did it.
If you decide to get one you also need a timing cover gasket, a pair of water circulating pump gaskets and some Mercruiser Perfect Seal, the best gasket compound in the universe. You can't get the timing cover off without removing the oil pan. If your oil pan gasket isn't new get a 1 piece reusable type.

 

[bruceb58]

Re: 1984 5.7L thunderbolt 4 timing chain question

Taking the oil pan off requires removing the engine. I would think long and hard before doing that.

 

[NHGuy]

Re: 1984 5.7L thunderbolt 4 timing chain question

Yup, it shouldn't be needed. The issue is power and missing right?

 

[Tail_Gunner]

Re: 1984 5.7L thunderbolt 4 timing chain question

measure your damper, buy a timing tape for the correct diameter damper. use your point and shoot to measure.

VP puts on timing tape from the factory, at least my vintage they did.

That's the ticket right there. I am about to have my first adventure with a old mcm 454 and a tbolt 4 tomorrow. I will be the first to admit I have no hands on experience or a good working knowledge of tbe system. However from what I have read there is no crank sensor or cam sensor so......Like days of old you can set the intial timing then take the tape and watch it advance and if it is running correctly your home free. Now if I have this system right it...you can set it and after a good warm up run it up to 3200 take your hand and advance the dist to see if your pick up power or get a smother response...if you do lock it down and put the engine though its paces..launch hard launch to wot..long wot run etc....If she starts pinging or clattering your advancing the timing was wrong thing to do.

The engine is old and a lttle out of spec so manual timing can or may find the sweet spot..andi may be totally way of base but I will find out.

 

[bruceb58]

Re: 1984 5.7L thunderbolt 4 timing chain question

Now if I have this system right it...you can set it and after a good warm up run it up to 3200 take your hand and advance the dist to see if your pick up power or get a smother response...if you do lock it down and put the engine though its paces..launch hard launch to wot..long wot run etc....If she starts pinging or clattering your advancing the timing was wrong thing to do.

I probably wouldn't do that. Set it to spec and forget it. Someday you will get some gas that has a little bit less octane, have a little more load on board, might be a little hotter than normal and you will be pinging and not know it until you get a hole in your piston.

 

[Tail_Gunner]

Re: 1984 5.7L thunderbolt 4 timing chain question

I probably wouldn't do that. Set it to spec and forget it. Someday you will get some gas that has a little bit less octane, have a little more load on board, might be a little hotter than normal and you will be pinging and not know it until you get a hole in your piston.

Very true

 

[tfret]

Re: 1984 5.7L thunderbolt 4 timing chain question

I'll get the timing tape and check to see if the timing advance is working correctly. It'd be great if it were that easy but I'm not counting on that. Yeah I understand the dots lining up on the sprockets. If I can't get the cam card data for a stock cam then that will be the only thing I can do to tell if its set correctly. I'll buy the timing tape and let you know what I find out. I really appreciate all the help because I'm definitely no motor head.

 

[Tail_Gunner]

Re: 1984 5.7L thunderbolt 4 timing chain question

Don't complicate this... your cam is degreed in by timing marks ..now hotrodders like to split hair's and get everything down to 1000's. In the end it means very little....just ego vanity and the meaning of life.As Bruce stated set the timing to spec's take a timing tape to verify the advance is working and call it a day.

 

[Scott Danforth]

Re: 1984 5.7L thunderbolt 4 timing chain question

Don't complicate this... your cam is degreed in by timing marks ..now hotrodders like to split hair's and get everything down to 1000's. In the end it means very little....just ego vanity and the meaning of life.As Bruce stated set the timing to spec's take a timing tape to verify the advance is working and call it a day.

but some of us run advance cam timing, however not on a boat. run it straight up. ego and vanity and a bit more high RPM power on the street with the cam 4 degrees advanced .....

 

[tfret]

Re: 1984 5.7L thunderbolt 4 timing chain question

I totally agree. I'm not interested in modifying any setting or trying to hot rod the boat at all. That's not for me. I fear the discussion has gotten off course. I just want the boat to run right. It runs like crap when set to spec and runs much better when timing is advanced some, but still has issues. I'm just trying to figure out why so I can fix the problem, set it all to spec, and go skiing. I remember reading once a guy figured out he had the wrong rotor button. The notched ring that the sensor reads has X number of slots in it. I guess 4 cylinders have fewer slots that ones on an 8 cylinder, but apparently they will interchange. Can someone tell me how many slots the V8 rotor is supposed to have?

 

[Tail_Gunner]

Re: 1984 5.7L thunderbolt 4 timing chain question

but some of us run advance cam timing, however not on a boat. run it straight up. ego and vanity and a bit more high RPM power on the street with the cam 4 degrees advanced .....

I am one of those....my little 4.3 is living on the edge

 

[Scott Danforth]

Re: 1984 5.7L thunderbolt 4 timing chain question

I am one of those....my little 4.3 is living on the edge

in the boat, or in a car? I used to run my 3.8 liter Buick at 4 degrees of cam advance, and it pulled like a freight train up to the 8000 RPM rev limiter.