5.7L - Ignition Timing Confusion

[Nitro15]

I've been trying to reset the ignition timing on my 1997 215 EC with the 5.7L 2 Barrel Carburetor. However, the service manual & engine cover show different values for the correct timing advancement. The service manuals says 8 degrees BTDC & the engine cover says 10 degrees BTDC (I've attached pictures of both for reference). I know that 2 degrees is probably not a huge deal but it's making me question the "authenticity" of the information provided in the manual.

The timing tab on my balancer does not resemble the one shown in the manual & what's even stranger is that it's not "fixed" to the engine block. When I rotated the distributor cap during my last attempt to adjust the timing, the tab itself moved up & down the balancer without any visible indications of where TDC might be. Am I going crazy or does this particular engine have a special way to set the timing that's not outlined in the manual?

P.s. I made sure to ground the purple/ white jumper wire & have a timing light hooked up to spark plug #1.

 

[Nater Potater]

My take is to believe the decal on the engine. Also note the manual and decal differ in setting the idle speed, leading me to believe the manual might be a bit too “generic”.
A picture of the balancer and pointer would be helpful.

 

[Nater Potater]

And, Welcome to Club Searay! When you have time, please fill out some info about your boat and yourself. That way, people can know at a glance what you have, making them more inclined to offer advice based on their knowledge.

 

[scoflaw]

Should have included a pic of the moving tab. Yes you might be going crazy, never heard of such a thing. Maybe an illusion?

 

[Thornton69]

Maybe you are looking at the wrong manual? Thunderbolt V with carbs show 10 BTDC.
service manual 5&57.pdf (atlanticmobilemarine.com)
You should be using a timing light that allows you to select your desired advance and then just align the line on the dampener with the notch on the front cover.

 

[Nitro15]

My take is to believe the decal on the engine. Also note the manual and decal differ in setting the idle speed, leading me to believe the manual might be a bit too “generic”.
A picture of the balancer and pointer would be helpful.

You're right, I should've taken a picture of the balance & pointer. I'll get one & report back!

 

[km1125]

I would definitely trust the engine sticker before the book.

Post a pic of the timing tab.

 

[Nitro15]

Maybe you are looking at the wrong manual? Thunderbolt V with carbs show 10 BTDC.
service manual 5&57.pdf (atlanticmobilemarine.com)
You should be using a timing light that allows you to select your desired advance and then just align the line on the dampener with the notch on the front cover.

You know, I had actually been referencing that manual for quite some time until I noticed that it specified a different spark plug type/ gap (AC-MR43T, .035" gap vs AC-MR43LTS, .045" gap). And I believe my engine is the "MCM 5.7 Alpha" as opposed to the "MCM 5.7 Alpha Bravo"... Again, very confusing to me since I can't seem to get a definitive answer on which manual I should be using. When I bought the boat, it didn't come with a full service manual unfortunately.

 

[Nitro15]

I would definitely trust the engine sticker before the book.

Post a pic of the timing tab.

That is my initial thinking too... I'll definitely get a picture ASAP.

 

[Skybolt]

I've been trying to reset the ignition timing on my 1997 215 EC with the 5.7L 2 Barrel Carburetor. However, the service manual & engine cover show different values for the correct timing advancement. The service manuals says 8 degrees BTDC & the engine cover says 10 degrees BTDC (I've attached pictures of both for reference). I know that 2 degrees is probably not a huge deal but it's making me question the "authenticity" of the information provided in the manual.

The timing tab on my balancer does not resemble the one shown in the manual & what's even stranger is that it's not "fixed" to the engine block. When I rotated the distributor cap during my last attempt to adjust the timing, the tab itself moved up & down the balancer without any visible indications of where TDC might be. Am I going crazy or does this particular engine have a special way to set the timing that's not outlined in the manual?

P.s. I made sure to ground the purple/ white jumper wire & have a timing light hooked up to spark plug #1.

So years ago there was a technical bulletin on all Chevy big block's that the timing should be changed to 8 degrees instead of the 10 on the sticker. The reason is there was a lot of holes being burned into the piston's from 10 degrees.

 

[Thornton69]

You know, I had actually been referencing that manual for quite some time until I noticed that it specified a different spark plug type/ gap (AC-MR43T, .035" gap vs AC-MR43LTS, .045" gap). And I believe my engine is the "MCM 5.7 Alpha" as opposed to the "MCM 5.7 Alpha Bravo"... Again, very confusing to me since I can't seem to get a definitive answer on which manual I should be using. When I bought the boat, it didn't come with a full service manual unfortunately.

Alpha Bravo just indicates the manual covers both models. The manual you originally posted your pic from was likely for the the earlier Thunderbolt lV ignition systems which was 8 BTDC.

 

[Thornton69]

So years ago there was a technical bulletin on all Chevy big block's that the timing should be changed to 8 degrees instead of the 10 on the sticker. The reason is there was a lot of holes being burned into the piston's from 10 degrees.

Does that apply to Mercruiser's Thunderbolt ignition systems? Have never seen a bulletin for that.

 

[Nitro15]

Should have included a pic of the moving tab. Yes you might be going crazy, never heard of such a thing. Maybe an illusion?

I'm going to go with crazy lol on top of this, I have a leaking steering cooler that needs to be replaced by this weekend. That ought to be fun!

 

[Nitro15]

Alpha Bravo just indicates the manual covers both models. The manual you originally posted your pic from was likely for the the earlier Thunderbolt lV ignition systems which was 8 BTDC.

I got my information from Service Manual 17, see attached pictures.

 

[Thornton69]

Not sure what to say. In the bottom of the pages you posted, it says that manual covers both Tbolt lV and V. Follow what it says on your engine cover as others have advised.

 

[Skybolt]

Does that apply to Mercruiser's Thunderbolt ignition systems? Have never seen a bulletin for that.

Yes, when they were young over 20yrs ago. Crusader first released the bulletin then Mecr. Makes a difference (small) on fuel eco as well, crazy what 2 deg. will do.

 

[scoflaw]

2 deg won't do shit and it certainly won't be burning holes in pistons. Fake News.

 

[techmitch]

2 deg won't do shit and it certainly won't be burning holes in pistons. Fake News.

Easy.

 

[Bill Curtis]

I've been trying to reset the ignition timing on my 1997 215 EC with the 5.7L 2 Barrel Carburetor. However, the service manual & engine cover show different values for the correct timing advancement. The service manuals says 8 degrees BTDC & the engine cover says 10 degrees BTDC (I've attached pictures of both for reference). I know that 2 degrees is probably not a huge deal but it's making me question the "authenticity" of the information provided in the manual.

The timing tab on my balancer does not resemble the one shown in the manual & what's even stranger is that it's not "fixed" to the engine block. When I rotated the distributor cap during my last attempt to adjust the timing, the tab itself moved up & down the balancer without any visible indications of where TDC might be. Am I going crazy or does this particular engine have a special way to set the timing that's not outlined in the manual?

P.s. I made sure to ground the purple/ white jumper wire & have a timing light hooked up to spark plug #1.

Another problem is that since it is a '97, something may have been changed. On my 95, everything looks like factory original with the 7.4L B3 decals on the valve covers and air cleaner cover. When I took a picture of the engine SN tag on the block and matched with the engine cover, the SN matched. Looking closely, a new SN tag was put on the engine cover.

Checked the SN against the Mercruiser engine ID charts / parts lists and found out the engine is a 454 Magnum block, heads and intake. Original engine was a 7.4L and it seams that the long block was changed out, using original 7.4L B3 valve covers and 7.4 B3 engine cover. The idle speed and max RPM numbers on the engine cover are for 7.4L, not the 454 Mag engine. Timing (8 deg BTDC) and spark plugs are the same.

PS: I have also seen some references saying my timing is 10 deg and others saying 8 deg. I stick with the 8 deg.

 

[Nitro15]

Here's pictures of both the timing marks & pointer. Am I correct in assuming that's the "fixed" pointer circled in red? (The degree marks are to the left on the photo of the balancer, a bit hard to see. Also strange that the BTDC marks are to the right of 0?)