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older 4 cylinder mercruiser Identification?

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I have a 1969 boat with a 4cyl 120 engine (original) in it... it is a chevy engine with an iron block and head.
im looking to identify what it is exactly. the engine serial number is 1M08158RS.
block casting numbers are 1409 7080.... and 224 97
there are no other numbers I can find on the exterior of the block.....

I have looked thru all the chevy data bases online that I could find, but nothing that will decode this engine....

once I get the engine identifed, I hope to get the timing specs for it, as it is pinging on acceleration using non-ethanol gas, otherwise its a strong running engine.... any help here would be appreciated. Thanks
 
it a 153CID inline 4 cylinder GM engine....nothing magical about it.

I doubt that you will find a timing curve in the factory manual...they didn't publish them in that time frame. Even if they did, the gasoline available today isn't what existed back them so I'd treat anything found very conservatively.

If its pinging and its original, I'd think the distributor needs to be serviced.....at a minimum....the weights may be ok but the springs have got to see some fatigue by now .... after 50 years....
 
Yes, I do believe its a 153ci, but what I have read there is a serial number break about the time this engine would have been built, which has a different initial advance setting.
I was hoping someone had the key to deciphering the engine code for the 4 cylinder GM engines. there is lots of info explaining this on the big blocks, small blocks and 6cylinders, but not the 4 cylinder engines.

this is the original engine for the boat, but the engine has been rebuilt... then before it could be dialed in, health problems forced the project to be put aside, and it sat in a barn for several years.. and now I own it.

the engine runs out and pulls great, but it pings and doesnt idle too well below a thousand RPM...... when I checked the timing, its advanced off the indicator plate to what I figure to be about 16 degrees BTDC... which leads me to believe they got the timing marks off on the gears..

at this time im pulling the timing cover to check the gear set timing. I have a piston-stop and dial indicator for the valves, but I cant find the specs for the valve timing....

just this morning I found what I think the "initial advance" timing for the distributor should be.. 6BTDC, but im not sure what my actual serial number is, but only the engine code that is stamped in the block at the base of the distributor, which is not in the same format as the serial numbers shown in the serial number break information...
 
...........
the engine runs out and pulls great, but it pings and doesnt idle too well below a thousand RPM...... when I checked the timing, its advanced off the indicator plate to what I figure to be about 16 degrees BTDC... which leads me to believe they got the timing marks off on the gears..
I'm with Mark on this one. Compromised flyweight return springs will allow for too much advance/too early.

at this time im pulling the timing cover to check the gear set timing. I have a piston-stop and dial indicator for the valves,
When a PPS (positive piston stop) is used, there is no need for a dial indicator. You will use the PPS and a degree wheel.
Once true TDC is established, then you would use a degree wheel and dial indicator to see if the camshaft is phased correctly with the crankshaft.
However, this may not be necessary if your concern is camshaft/crankshaft indexing. (see below)

If you are wanting to see if the harmonic balancer is indexed correctly (outer ring has not slipped on the inner hub)... then yes... use the PPS procedure!

but I cant find the specs for the valve timing....
You should see the timing chain sprocket indexing marks similar to that of the SBC.

just this morning I found what I think the "initial advance" timing for the distributor should be.. 6BTDC, but im not sure what my actual serial number is, but only the engine code that is stamped in the block at the base of the distributor, which is not in the same format as the serial numbers shown in the serial number break information...
Whether 6, 5 or 7 degrees BTDC, this is BASE advance, and is without any mechanical advancing.
Once out of idle RPM, the mechanical advance system will begin to add to the BASE value.
 
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the base timing is what Im looking for at this time....

the flyweights are in good condition and working as they should...

what I have found so far after getting the front cover off, is the marks are mated correctly in relation to one another, BUT.... at TDC, the dot marks on the gears are about 1 tooth away from where they should be... instead of them being at their closest point to one another, TDC comes up before the marks get to their closest point (a strait line from the center of the crank rotation to the center of the cam rotation, the marks should center and line up perfectly behind this line)....
the indicator mark on the crank timing gear seems to be off 1 tooth, as one of the valves is still open slightly... it appears the cam is retarded 1 tooth.

to solve the problem, I have loosened the rockers and removed the lifters, then pulled the cam and rotated/advanced it one tooth to the position it where it should be in relation to true TDC (the gears are pressed on, both the crank and the cam).... now, after replacing the lifters in #1 cyl, the valves are both fully closed and I can rotate the crank back and forth several degrees without movement in either of the #1 lifters.

now, if I knew what the valve lift was supposed to be at what crank position, I could confirm that it is in fact, only one tooth off...
 
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Manual Number 1 covers those engines made in the 1960's....it states initial timing is 8 deg BTDC, except for those engines using distributor #1112467, which use 6 deg.
These are all assuming leaded fuel with a minimum research octane of 93...

Manual 2 covers the early 70's vintage and states 8 deg BTDC and that 1974 and earlier models require leaded fuel or they may suffer valve seat failure. It also states that lower octane fuel may be used but to reset initial timing to 4 deg BTDC. That manual also provides a timing curve with full advance ~ 2100 RPM with 25-29 deg advance...

There is nothing in either manual regarding valve timing...you will have to do some research there if you want those numbers....
 
Manual Number 1 covers those engines made in the 1960's....it states initial timing is 8 deg BTDC, except for those engines using distributor #1112467, which use 6 deg.
These are all assuming leaded fuel with a minimum research octane of 93...

Manual 2 covers the early 70's vintage and states 8 deg BTDC and that 1974 and earlier models require leaded fuel or they may suffer valve seat failure. It also states that lower octane fuel may be used but to reset initial timing to 4 deg BTDC. That manual also provides a timing curve with full advance ~ 2100 RPM with 25-29 deg advance...

There is nothing in either manual regarding valve timing...you will have to do some research there if you want those numbers....


I just downloaded Manual #1... its a big manual with lots of sections. do you happen to know/remember what page talks about the timing, fuel octane and the different model distributor?
 
..............
the base timing is what Im looking for at this time....
the flyweights are in good condition and working as they should...
When you finally get it up and running, connect your timing light, set BASE advance, and then increase RPM to see if the system is advancing correctly.

As per Mark, you will be looking for 25-29 deg advance @ 2,100 RPM
(to me, that appears to be somewhat aggressive)


If you are uncertain, and/or if your fuel's octane rating is rather low, favor the 25 degrees @ 2,100 RPM.

Suggestion:
Get your hands on a year-correct OEM service manual for this engine, and follow the ignition advance specs.
See if you can find an actual ignition advance curve graph for this engine, and then strobe your timing marks to verify that your system is delivering it correctly.

what I have found so far after getting the front cover off, is the marks are mated correctly in relation to one another, BUT.... at TDC, the dot marks on the gears are about 1 tooth away from where they should be... instead of them being at their closest point to one another, TDC comes up before the marks get to their closest point (a strait line from the center of the crank rotation to the center of the cam rotation, the marks should center and line up perfectly behind this line)....
the indicator mark on the crank timing gear seems to be off 1 tooth, as one of the valves is still open slightly... it appears the cam is retarded 1 tooth.
Not good!

to solve the problem, I have loosened the rockers and removed the lifters, then pulled the cam and rotated/advanced it one tooth to the position it where it should be in relation to true TDC (the gears are pressed on, both the crank and the cam)....
The camshaft chain sprocket may be a tight fit, but when the bolt is removed, it should come off fairly easily.
The crankshaft chain sprocket will be a press fit, and will be keyed to the crankshaft.

Between the camshaft alignment dowel, the crankshaft key, and when the chain sprocket indexing "dots" are aligned, the crankshaft and camshaft should be indexed correctly.


now, after replacing the lifters in #1 cyl, the valves are both fully closed and I can rotate the crank back and forth several degrees without movement in either of the #1 lifters.
Yes.... that would be correct!

now, if I knew what the valve lift was supposed to be at what crank position, I could confirm that it is in fact, only one tooth off...
With #1 cylinder's piston at TDC, and with both chain sprocket "dots" aligning, there should be no need to do that...... unless of course, you want to verify that the balancer TDC line mark is accurate.



Now, when you adjust the cam followers, start with #1 cylinder at TDC C/S.
Adjust both intake and exhaust (you will be setting the depths of the hydraulic plungers).

Now move the crankshaft 180*, and do the same to #3 intake and exhaust.
Follow that with another 180* rotation, and do the same to #4 cylinder.
Rotate another 180*, and do same for #2.

After that, roll the crankshaft again so that #1 cylinder piston stops at approx 6* BTDC on the compression stroke.
Install the distributor and spark plug cables.
With a spark detector (or spark plug) in the #1 plug cable boot, turn the ignition key ON.
Now rotate the distributor in the CCW direction until you see one spark event.
Do this several times until you are able to stop rotating the housing the moment of the spark event.
Tighten the distributor's clamp bolt.

Now it should fire right up.
Soon at it fires up, set BASE advance, and re-check the clamp bolt for tightness.


GM 3.0 timing set indexing marks.jpg


.
 
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If you are wanting to see if the harmonic balancer is indexed correctly (outer ring has not slipped on the inner hub)...

Ayuh,.... I don't have much to add, other than the fact that the 153", 120 hp motors don't have a harmonic balancer,......

If there's a harmonic balancer on it,...... It's a 181", 140 hp motor,......
 
Ayuh,.... I don't have much to add, other than the fact that the 153", 120 hp motors don't have a harmonic balancer,......

If there's a harmonic balancer on it,...... It's a 181", 140 hp motor,......

Bill, are you certain about that?

This is listed as a Mercruiser 2.5L 55045T harmonic balancer.

61bMVo1TWzL._SX425_.jpg




https://www.ebay.com/p/17016718544?...S12m5rDBrUNytgt8ZdynHSzpfrRwMRfcaAtlUEALw_wcB



Also, I think that I was incorrect regarding the chain/sprocket timing set.

It looks like the 2.5L may have used a gear set.


GM 3.0 timing set indexing marks.jpg



.
 
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Bill, are you certain about that?

This is listed as a Mercruiser 2.5L 55045T harmonic balancer.

61bMVo1TWzL._SX425_.jpg




https://www.ebay.com/p/17016718544?...S12m5rDBrUNytgt8ZdynHSzpfrRwMRfcaAtlUEALw_wcB



Also, I think that I was incorrect regarding the chain/sprocket timing set.

It looks like the 2.5L may have used a gear set.


View attachment 22267

that balancer is what mine looks like.... I have also read that the 153 (2.5) does not have a harmonic balancer, but it seems this may be incorrect.... which is one of the reasons I was looking to get the engine code deciphered, to find out what it actually is... it says 120 on the outdrive and its supposed to be the original engine for the boat, which is why I assume it is a 153ci...

I called the lady I got the boat from and she believes, but isnt sure if her husband had the original engine rebuilt or replaced it with a long block, or installed a completely different engine... but he passed on before the boat was running correctly.

also, the cam timing gear has no retaining bolt, but is firmly pressed on, as is the crank gear.... I talked to a machine shop and they said these are serviced by removing the cam/crank from the block to remove and replace the gears, if needed.... the cam itself has a thrust retainer held by screws that are accessed thru the holes in the gear.
 
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at TDC (checked by piston stop), and with the crank keyway is at 12:eek:'clock as it should be, the gears mesh like this... it looks as if the crank gear dot should be advanced 1 tooth, so that the dot on the cam gear could mesh properly.

the crank rotates to the right, turning the cam gear to the left.. this shows the cam to be retarded 1 tooth due to the crank gear being indexed wrong...
but im not sure that the position, set up as shown would cause a need for the base timing to have to be 16degrees advanced to make it run...

and, by advancing the cam gear 1 tooth so it meshes as it should (regardless of the dots on the gears), will that allow the base timing to be retarded from 16 BTDC, back to its spec position at 6-8 BTDC?...


20191113_103638.jpg
 
If what you listed as the 'serial number' in your original post is really the engine code (which is consistent with the latter info),

then you don't have the original engine, you have a much newer 181 CID block.

regarding the cam gear phasing, there's nothing wrong that I can see in your picture - the crank's absolute position in the block is irrelevant.
 
Bill, are you certain about that?

This is listed as a Mercruiser 2.5L 55045T harmonic balancer.

61bMVo1TWzL._SX425_.jpg




https://www.ebay.com/p/17016718544?...S12m5rDBrUNytgt8ZdynHSzpfrRwMRfcaAtlUEALw_wcB



Also, I think that I was incorrect regarding the chain/sprocket timing set.

It looks like the 2.5L may have used a gear set.


View attachment 22267



.

rick if you look through the excellent parts diagrams on this site all of the 110/120/2.5 engines have a hub and pulley where all the 3.0s have a harmonic balancer so if the op does have a balancer it is likely this is a 3.0 replacement as it is a drop in swap.

Also yes yes all the Chevy inline 4 & 6 cylinders use a timing gear drive vs chain as seen on most other V engines
 
at TDC (checked by piston stop), and with the crank keyway is at 12:eek:'clock as it should be, the gears mesh like this... it looks as if the crank gear dot should be advanced 1 tooth, so that the dot on the cam gear could mesh properly.

the crank rotates to the right, turning the cam gear to the left.. this shows the cam to be retarded 1 tooth due to the crank gear being indexed wrong...
but im not sure that the position, set up as shown would cause a need for the base timing to have to be 16degrees advanced to make it run...

and, by advancing the cam gear 1 tooth so it meshes as it should (regardless of the dots on the gears), will that allow the base timing to be retarded from 16 BTDC, back to its spec position at 6-8 BTDC?...


View attachment 22269
agree with mako mark these look correct
 
If what you listed as the 'serial number' in your original post is really the engine code (which is consistent with the latter info),

then you don't have the original engine, you have a much newer 181 CID block.

regarding the cam gear phasing, there's nothing wrong that I can see in your picture - the crank's absolute position in the block is irrelevant.

the engine code I have listed is correct, and if it decodes as a 181 and not the 153, this would explain a couple things ive wondered about.... and way helpful in getting it set up to spec.

the cranks absolute position is irrelevant?... even if one of the marks shown is in the wrong place?.... I called several cam manufactures today and Isky Cams is the only one with an engineer available to talk to about the problem. he said exactly what I suspected but wanted to hear from someone else. IF the can was retarded in relation to its designed position of the crank, the base timing would have to be many degrees advanced of where it should be.... he agreed that a gear being indexed wrong was not common but it does happen, causing problems like this.... If this is in fact the problem here, this will be the second time in my life that Ive had this issue...(firts time was on a dodge 360 engine)....

I have reassembled the engine this afternoon and will see how it runs tomorrow....

EDIT... using the idea that it may be a 181, I was able to look it up and fine it to be a 1987 181ci engine.... this doesnt solve my problem, but its a start...

and a BIG thank you for the help in determining what im working on.
 
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what im having trouble with now is finding a manual or timing specs for a carbed 181ci with a conventional distributor.... does anyone have a lead on this information?
 
.................
regarding the cam gear phasing, there's nothing wrong that I can see in your picture - the crank's absolute position in the block is irrelevant.
I agree with Mark.

**
Since the crankshaft gear is indexed to the crank via a key and key-way, there is no changing this.
Since the camshaft gear is also indexed to the cam (most likely doweled), there is no changing this (unless you enlarge the alignment dowel bore and use eccentric bushings).
As long as the two dots align, all else is irrelevant.


rick if you look through the excellent parts diagrams on this site all of the 110/120/2.5 engines have a hub and pulley where all the 3.0s have a harmonic balancer so if the op does have a balancer it is likely this is a 3.0 replacement as it is a drop in swap.
I see!
Thank you.


Also yes yes all the Chevy inline 4 & 6 cylinders use a timing gear drive vs chain as seen on most other V engines
Let me ask you honestly...... why then (when I do a search) am I seeing chain/sprocket timing sets for these engines?

agree with mako mark these look correct

Ayuh,..... Sure as 'ell,......
Bill, I trust your expertise..... however, why am I seeing a harmonic balancer listed for the 2.5L 4 banger?
Are these ads incorrect???


if the engine code I have listed is correct, and if it decodes as a 181 and not the 153, this would explain a couple things I've wondered about.... and way helpful in getting it set up to spec.
I would think so.

Quote from Mark: "the cranks absolute position is irrelevant?" even if one of the marks shown is in the wrong place?....
Centerline, from what you have shown us, your marks are aligning correctly.
See ** above.

I called several cam manufactures today and Isky Cams is the only one with an engineer available to talk to about the problem. he said exactly what I suspected but wanted to hear from someone else.
See ** above.

IF the cam was retarded in relation to its designed position of the crank, the base timing would have to be many degrees advanced of where it should be....
Ignition timing relates to the position of the piston within the cylinder.
In other words, we want the spark event to occur during a certain crankshaft angle BTDC.
Example:
6* of BASE advance occurs when the crankshaft is 6* from placing the piston at Top Dead Center.


For the Hot Rod enthusiasts, they may retard or advance the valve timing, but not necessarily the ignition timing.

he agreed that a gear being indexed wrong was not common but it does happen, causing problems like this.... If this is in fact the problem here, this will be the second time in my life that Ive had this issue...(firts time was on a dodge 360 engine)....

I have reassembled the engine this afternoon and will see how it runs tomorrow....
Just make sure that when you roll the crankshaft around, that for every 2 crankshaft revolutions, the two marks align as you have shown in your image.
This appears to be correct!

attachment.php


If you change this indexing, your camshaft and crankshaft will be out-of-phase with one another.

what im having trouble with now is finding a manual or timing specs for a carbed 181ci with a conventional distributor.... does anyone have a lead on this information?
What you are after would be an ignition advance curve graph.

FYI: BASE advance is BASE advance.... all day, and all day long.
We fire up on BASE, and we idle on BASE..... and that's about it.
Your engine should fire up on and idle on 6* to 8* of BASE advance.

More importantly will be what the advance is doing during the "progressive" advance curve, and at the "full-in" RPM.
Think of it like this:
Ignition advance is given the "last word" regarding the LPCP (location of peak cylinder pressure).
A good LPCP creates torque.
A lazy LPCP leaves power and torque on the table.
Excessive advance will cause destructive Detonation!

After you have verified true TDC markings, strobe your timing marks.
Watch the advance as you increase RPM.
If Marks timing specs are correct (
25-29 deg advance @ 2,100 RPM), you should see a progressively advancing spark event, and you should see the spark event reach it's limit.
This "limit" is your "Full-In" advance.

(personally, I think that
25-29 deg advance @ 2,100 RPM is rather aggressive for this engine)

But let's run with a BASE of 6* and a total advance of 25* @ 2,100 RPM.
At 2,100 RPM, your strobe light should be seeing 25* advance.
If not, make an adjustment to the distributor housing, and lock it down.
Check the advance again.
When back at idle RPM, see where the BASE advance is.
If BASE is at 6*, you are good to go.
If BASE is at 8*, and if the engine will not "buck" during cranking, you are good to go.
If by chance BASE is at only 4*, or is at 10*, you will need to make changes within the distributor.


When/if you do find an OEM ignition advance curve for this engine, it will look similar to this one below.
Note that the vertical scale does not include the BASE advance value.
Add the BASE advance value to this, and you will have your actual dynamic advance value.

Example only... do not use this data.

fetch








,


.

 
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what im having trouble with now is finding a manual or timing specs for a carbed 181ci with a conventional distributor.... does anyone have a lead on this information?

The manual covering the mid-late 1980's inline four cylinders shows a timing curve consistent with the data provided in Post #6, for the Delco distributor. The Prestolite distributor curves, in the manual covering the later engines, is much more conservative, showing a two slope curve. the nominal values for the breakpoints are 0 deg @ 1000 RPM, 10 deg @ 1400 RPM, and 16 deg @ 4100 RPM - these are +/- two degrees and suggest an initial value of 8 deg BTDC....and these are all carb'd
 
Bill, I trust your expertise..... however, why am I seeing a harmonic balancer listed for the 2.5L 4 banger?
Are these ads incorrect???

Ayuh,..... That would be my guess,.....

I trust the parts listin's here at marine engines way more than ads on ebay,......
 
Rick

why you see chain sets sets listed for a gear drive application is based on a quick google search

1. Not actually for a 3.0 but another GM engine
2. Apparently merc makes a 3.0 TDI diesel that uses a chain but is a completely different engine family
3 misnomer being on a parts page of many different engines timing sets where chains and Cam and crank sprockets are listed one these pages no part number is actually listed for a chain for the 2.5/3.0

you have to look close and know what you are looking for. Would also reinforce Bondos comments that the parts listings here on marine engine are to me the most useful and accessible drawings etc. when I repowered from a 4.3 to a 5.0 buying just a base engine they were invaluable in helping determine what could carry over to the new engine
 
I did find the torque curve for the 181cid in the industrial engine manual....and a lot more information about it.
http://www.allpowerlabs.com/wp-content/uploads/2015/05/GM_PSI-3.0L-Engine-Service-Manual.pdf

all my questions have been answered to this point... thanks everyone

You want to see an ignition advance curve for the Marine engine, not necessarily a torque curve.

Also, from what I see, that is a manual for the industrial 3.0L engine, EST ignition system, and it discusses the specs for use of gasoline, LPG and NG.
 
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after running the engine on the muffs with the cam gear advanced 1 tooth from the index marks, the engine will now idle down to 550 and will run with the distributer at 6 BTDC base timing. the total advance is 26degrees @ 3200rpm.... it isnt too smooth, but has a bit of a kick to it when idling
(i did not see what rpm the advance tops out at, but it is topped out at 3200)

before the cam adjustment, I could only get the base timing down to about 12BTDC and then it would cough kick and die.... and would not idle below 1000rpm.

its still isnt right but seems to run much closer to where it should be....
 
I indexed the balanced using timing tape, and played with it some more and found it runs smoothest at 10BTDC base timing, which is 32BTDC maximum..... we are taking it to the water today for its second test run....
 
I indexed the balanced using timing tape, and played with it some more and found it runs smoothest at 10BTDC base timing, which is 32BTDC maximum..... we are taking it to the water today for its second test run....

FYI....... The timing tape or Degree Decal (such as Mr. Gasket or MSD) must be a match for the harmonic balancer diameter.
shopping


To avoid any engine damage, favor the low side of ignition advance until you get things sorted out.
 
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