Mercruiser Setting Timing on 3.0L

[ESGWheel]

Dan,
Long post but please read thoroughly.
Enthusiasm is great but let’s think thru a few things first and come up with a plan. Here are my suggestions and questions.

1. Did you rerun the motor post confirming the FO and then pulling the plug wires one at a time?
   • If not, please do as this will validate your compression readings and post results
2. Do you own an air compressor?
   • If not then a leak down tester will do you no good, need one to use it.
   • But let’s say you do have one or access to one (even one of those pancake types that carpenters use will work), getting a leak down tester is not going to be a good investment for you IMO. These are used as a diagnostic device for folks that do a lot of work on engines to help them determine the extent of the issues - prior to tearing it down - to then provide the customer a better estimate of costs to come. The damage your engine has will not change and the costs will be what they are. You will be able to afford it or not depending on damage. IF you still desire to do a leak down test, can do a poor man’s leak down as mentioned by Mike in post #17 and me in #7. If want to do this reply: “Please explain how” and we’ll walk you thru it.

Post doing all the above, assuming bad (expected) results of item 1, let’s get into it and pull the head to see where its at. Do so by first taking a lot of pictures of it all assembled. Keep everything ORGANIZED and CLEAN as you pull it apart. One method I use is to have a bunch of plastic zip (sandwich) bags including the larger quart size and a sharpie marker. And then mark a bag with the items and place into the bag. Example: marked with “Valve Cover Bolts” and then place them in that bag as you pull them out. Also have a roll of painter’s tape and can use that to tag things that do not fit into a bag. Example: your pushrods > need to keep them in order so put a little tag on each one as you pull it out, thus they are numbered 1 thru 8 starting from the front. Make sense? Take pics along the disassembly, like once the head is pulled but (hopefully) the gasket is still on the block > pic of that. The carefully peel off gasket > pic of it and the block and the bottom of the head. Post them.

A quick google search provided what seem to be good videos on this process:

• Part 1 Disassembly link
• Part 2 Assembly link

Yes, the gaskets are inexpensive, and Mike provided a link as well. The key is a marine type (no carbon steel due to marine environment).

As for “have I ever done a head gasket on a 3.0.” No. But lot of them on Volvo B18 motors (also a 4 cylinder). Was typically not due to blowen or other issues with the motor, perhaps a little detonation (pinging). My boss at the time was a great salesman and we would decarb these high mileage motors left and right because he convinced the owners that is how to keep them going. He was not wrong, but he oversold if you follow my meaning. And a whole bunch on the interference engines in Fiat Spiders. The cam belt would typically break at 31,000 miles (warranty expired at 30k) and bam! Head is coming off due to bent valves. And a bunch of others (v6, V8s). I digress but was fun walking down memory lane, so thx for the question!

Oh before I forget, one tool you will need are thread chasers, not taps, chaser, like this link. See post 13 of this tread for why.

 

[kd4pbs]

Here it is running and idleing in neutral... To me it seems like its running good, althought could be better. If it didnt have compression in 2 out of 4 cylinders there is no way it would run like that...

Yeah - that guy is running on two cylinders. 2&3 are 180 degrees away, so the engine goes fire-miss-fire-miss-fire-miss-fire-miss-fire-miss.... Makes it easier to hide the failures.
Odd that a head gasket would be so blown as to give you 0PSI compression. That would be a VERY blown head gasket! If I were you, I'd make sure the suspect cylinders were half way on the upstroke of the compression stroke and use your borescope to verify the valves are closed fully. If the head gasket is blown so severely as to give basically 0PSI compression, you should be able to see the lack of a fire ring between the head and block on your borescope.
Then again, no matter what the issue actually is, you're taking the head off anyway, so you might as well ignore everything I just wrote
Just prepare yourself that it might be something additional than just a blown head gasket.

 

[ESGWheel]

Then again, no matter what the issue actually is, you're taking the head off anyway, so you might as well ignore everything I just wrote

LM@O!
Edit: and thanks for the chuckle! I needed it...

 

[kd4pbs]

Thanks - I'll be here all week! Don't forget to tip your waitress!
Dan - be sure that you verify the head is not warped. If there's any question about it, it's much cheaper and easier to address it while you've got it apart than to do the job twice. That being written, it's not a very difficult task, especially with the help of those around here. You've got good access around that engine to make it happen without any "gotchas" along the way.

 

[DanOnTheBoat]

Dan,
Long post but please read thoroughly.
Enthusiasm is great but let’s think thru a few things first and come up with a plan. Here are my suggestions and questions.

1. Did you rerun the motor post confirming the FO and then pulling the plug wires one at a time?
   • If not, please do as this will validate your compression readings and post results
2. Do you own an air compressor?
   • If not then a leak down tester will do you no good, need one to use it.
   • But let’s say you do have one or access to one (even one of those pancake types that carpenters use will work), getting a leak down tester is not going to be a good investment for you IMO. These are used as a diagnostic device for folks that do a lot of work on engines to help them determine the extent of the issues - prior to tearing it down - to then provide the customer a better estimate of costs to come. The damage your engine has will not change and the costs will be what they are. You will be able to afford it or not depending on damage. IF you still desire to do a leak down test, can do a poor man’s leak down as mentioned by Mike in post #17 and me in #7. If want to do this reply: “Please explain how” and we’ll walk you thru it.

Post doing all the above, assuming bad (expected) results of item 1, let’s get into it and pull the head to see where its at. Do so by first taking a lot of pictures of it all assembled. Keep everything ORGANIZED and CLEAN as you pull it apart. One method I use is to have a bunch of plastic zip (sandwich) bags including the larger quart size and a sharpie marker. And then mark a bag with the items and place into the bag. Example: marked with “Valve Cover Bolts” and then place them in that bag as you pull them out. Also have a roll of painter’s tape and can use that to tag things that do not fit into a bag. Example: your pushrods > need to keep them in order so put a little tag on each one as you pull it out, thus they are numbered 1 thru 8 starting from the front. Make sense? Take pics along the disassembly, like once the head is pulled but (hopefully) the gasket is still on the block > pic of that. The carefully peel off gasket > pic of it and the block and the bottom of the head. Post them.

A quick google search provided what seem to be good videos on this process:

• Part 1 Disassembly link
• Part 2 Assembly link

Yes, the gaskets are inexpensive, and Mike provided a link as well. The key is a marine type (no carbon steel due to marine environment).

As for “have I ever done a head gasket on a 3.0.” No. But lot of them on Volvo B18 motors (also a 4 cylinder). Was typically not due to blowen or other issues with the motor, perhaps a little detonation (pinging). My boss at the time was a great salesman and we would decarb these high mileage motors left and right because he convinced the owners that is how to keep them going. He was not wrong, but he oversold if you follow my meaning. And a whole bunch on the interference engines in Fiat Spiders. The cam belt would typically break at 31,000 miles (warranty expired at 30k) and bam! Head is coming off due to bent valves. And a bunch of others (v6, V8s). I digress but was fun walking down memory lane, so thx for the question!

Oh before I forget, one tool you will need are thread chasers, not taps, chaser, like this link. See post 13 of this tread for why.

Read every word lol...

No I haven't run the engine after I did the compression test. I will run the engine tomorrow since I am getting a pressure tester tomorrow so it'll be an engine work day tomorrow lol. I will do the spark plug pull test and I will let you guys know what happens to the engine. I will also try and figure out how the pressure tester works. I indeed do have an air compressor. From the list of tools that you gave me I'd only need to buy the torque wrenches lol. Well and the thread chaser.

That all makes sense! And good idea, I was actually thinking the same, I was going to take videos and a bunch of pictuires anyways, and label all the wires with painter's tape.

Ah yes Dale, I've watched those 2 videos of his 5 times each already... He also has a 3rd video because his engine overheated againa d he blew the head gasket again. This is the video:

(sorry not sure how you did the "link" thing lol)

I was going to ask about if i could use a car head gasket, a metal one, but thanks for letting me know. I also found a full gasket kit on Amazon. Its a MANHLE HS5719. I've read online about this company and they seem really good from what people are saying... It is $140 CAD...

MANHLE KIT: https://www.amazon.ca/gp/product/B007ZJKGP8/ref=ewc_pr_img_2?smid=A2SNKCOWT2PS9P&psc=1

Although I did find the Sierra one I think the exact same one Dale used in his engine. Its about $65

 

[DanOnTheBoat]

Yeah - that guy is running on two cylinders. 2&3 are 180 degrees away, so the engine goes fire-miss-fire-miss-fire-miss-fire-miss-fire-miss.... Makes it easier to hide the failures.
Odd that a head gasket would be so blown as to give you 0PSI compression. That would be a VERY blown head gasket! If I were you, I'd make sure the suspect cylinders were half way on the upstroke of the compression stroke and use your borescope to verify the valves are closed fully. If the head gasket is blown so severely as to give basically 0PSI compression, you should be able to see the lack of a fire ring between the head and block on your borescope.
Then again, no matter what the issue actually is, you're taking the head off anyway, so you might as well ignore everything I just wrote
Just prepare yourself that it might be something additional than just a blown head gasket.

Thanks for the info! Ill try the compression test again tomorrow and see what I get. Maybe this time Ill warm up the engine because the compression readings I got were on a cold engine. I talked to my friend hes a car mechanic and he swapped head gaskets in the past. But he said it could be a piston issue, which I hope it isnt... But anyhow, Ill redo the compression and a pressure test as well. Ill post all pictures here!

 

[DanOnTheBoat]

Thanks - I'll be here all week! Don't forget to tip your waitress!
Dan - be sure that you verify the head is not warped. If there's any question about it, it's much cheaper and easier to address it while you've got it apart than to do the job twice. That being written, it's not a very difficult task, especially with the help of those around here. You've got good access around that engine to make it happen without any "gotchas" along the way.

Got it thanks for the heads up! Warped meaning not completely flat right? I'd have to "sand" it down or probably be better to take it to a machine shop? Or can I do Dales way lol?

 

[alldodge]

Flatness is done with a steel straight edge (can also use framing square) and feeler gauges. Lay edge of straight edge across head and see what the largest feeler gauge can but slipped under it.

Max 0.007 overall

 

[ESGWheel]

Dan,
Overall, there are a number of steps for this process, one of which is flatness. In brief they are:

1. Complete testing outlined above
2. Disassemble
3. Photos
4. Clean, clean, clean while also protecting debris from contaminating
5. Inspections for damage / veracity of components that include
   1. Flatness
   2. Cracks
   3. Valve sealing integrity
6. Fixing any issues found
7. Reassembly
8. Testing

My suggestion is to address the ‘how tos’ when that step is reached. It may take more time but that way you will have a good understanding as well as not leaving anything out.

Since the time between disassembly, clearing and that critical flatness check can be same day, outlined below are my How Tos for those steps. Others can add in as needed in case I missed something, etc.

• Step 1 Testing > already outlined
• Step 2 Disassemble > already outlined for organization, watch video and ask any questions not covered
• Step 3 Photos > already outlined
• Step 4 Cleaning > This is where a lot of paper towels, scrapers, solvents, block of wood and sandpaper come into play.
  • For the engine block, plug up all the ‘holes’, so oil passages, the pushrod holes, and the cylinders. I also do the bolt holes even though can blow out later, why crap them up. Water passage ok to leave open as debris will flush out. Start by spraying down each cylinder bore with WD40 and then stuff paper towels in there to fill the hole just shy of the top of the block. With other holes be careful as you do not want to stuff the towel into the oil / pushrod holes such that it disappears on you. Try rolling them up tightly, stuff a little bit into the hole (rest sticking out) and then cut it off. You can pull them out with a pair of needle nose pliers. Tapered corks work too, again cutting off what is above the deck. To pull those out, put in a screw and pull. The idea here is to simply prevent crap from getting into places where you do not want it.
  • Scrap away all the crap you can and then resort to the sanding block like in the video. Use 180 which is probably finer than others use and thus will take more time but better safe then sorry. The key here is to NOT remove any metal. DO NOT use power tools.
  • Using a solvent clean the heck out of it (like the video).
• Step 5.1 > Inspection: Flatness. This is where we hope all is good but need to check. With a good quality and not abused metal ruler / straight edge ideally at 2 feet long, check it first for straightness by laying in on a good flat smooth surface with paper under. Use a fine point pencil and draw a line the length of the ruler. Then flip it (so the left is now the right) and line it up with line and redraw that line (both lines are with the same edge). Look for the lines to be perfectly overlapped. If not, it’s not straight. Here is a video (link) on checking for flatness, many exist, so review a few and post results.

The rest of how to’s come after completion of 1 thru 5.1

 

[kd4pbs]

Excellent advice. And yes, if the head is warped (not flat) you'll be visiting a machine shop, unless you happen to have a large metal working mill and all the fixtures capable of swinging a cylinder head resurfacing tool
Pay no attention to those on the internets that try to convince you to use sandpaper and a flat surface or a DA power sander. I would not even trust that on a lawnmower.

 

[DanOnTheBoat]

Dan,
Overall, there are a number of steps for this process, one of which is flatness. In brief they are:

1. Complete testing outlined above
2. Disassemble
3. Photos
4. Clean, clean, clean while also protecting debris from contaminating
5. Inspections for damage / veracity of components that include
   1. Flatness
   2. Cracks
   3. Valve sealing integrity
6. Fixing any issues found
7. Reassembly
8. Testing

My suggestion is to address the ‘how tos’ when that step is reached. It may take more time but that way you will have a good understanding as well as not leaving anything out.

Since the time between disassembly, clearing and that critical flatness check can be same day, outlined below are my How Tos for those steps. Others can add in as needed in case I missed something, etc.

• Step 1 Testing > already outlined
• Step 2 Disassemble > already outlined for organization, watch video and ask any questions not covered
• Step 3 Photos > already outlined
• Step 4 Cleaning > This is where a lot of paper towels, scrapers, solvents, block of wood and sandpaper come into play.
  • For the engine block, plug up all the ‘holes’, so oil passages, the pushrod holes, and the cylinders. I also do the bolt holes even though can blow out later, why crap them up. Water passage ok to leave open as debris will flush out. Start by spraying down each cylinder bore with WD40 and then stuff paper towels in there to fill the hole just shy of the top of the block. With other holes be careful as you do not want to stuff the towel into the oil / pushrod holes such that it disappears on you. Try rolling them up tightly, stuff a little bit into the hole (rest sticking out) and then cut it off. You can pull them out with a pair of needle nose pliers. Tapered corks work too, again cutting off what is above the deck. To pull those out, put in a screw and pull. The idea here is to simply prevent crap from getting into places where you do not want it.
  • Scrap away all the crap you can and then resort to the sanding block like in the video. Use 180 which is probably finer than others use and thus will take more time but better safe then sorry. The key here is to NOT remove any metal. DO NOT use power tools.
  • Using a solvent clean the heck out of it (like the video).
• Step 5.1 > Inspection: Flatness. This is where we hope all is good but need to check. With a good quality and not abused metal ruler / straight edge ideally at 2 feet long, check it first for straightness by laying in on a good flat smooth surface with paper under. Use a fine point pencil and draw a line the length of the ruler. Then flip it (so the left is now the right) and line it up with line and redraw that line (both lines are with the same edge). Look for the lines to be perfectly overlapped. If not, it’s not straight. Here is a video (link) on checking for flatness, many exist, so review a few and post results.

The rest of how to’s come after completion of 1 thru 5.1

Thank you! I have nothing to say than will follow🫡 lol.

I seriously appreciate all the help you guys.

 

[DanOnTheBoat]

Also, I attempted to try and do a leak down test since I got a kit and I've come across a problem... I've searched online a bunch and Im not too sure of how to turn this engine over by hand... because getting in between the mount arm and crankshaft bolt is literally impossible and I heard that trying to turn the engine by the water pump won't do anything. I read about turning it over with the alternator but that would require to have the belt really tight and I dont want to risk snapping the belt...🫣

 

[ESGWheel]

I found this thread. I got there via Google. And no you will not snap the belt.

 

[DanOnTheBoat]

Hey guys, so I'm starting to look at everything that I will need to do this project with. I made a list of all the things I will need. Do I need any additionals or wanything removed? Any sealants? Sorry it's not neat...

TOOLS:
- EPAuto 1/4-Inch Drive Click Torque Wrench (20–200 in-lb / 2.26–22.6 N·m) — $45.97

https://www.amazon.ca/gp/product/B01LX4ND65/ref=ox_sc_act_title_1?smid=A1L7F5DL4H71TK&th=1

- Neiko 00339A 3/8-Inch Drive Breaker Bar, 12" Long — $19.14

NEIKO Premium 12-Inch Breaker Bar with Flexible 180-Degree Head

Neiko 00339A 3/8-Inch-Drive Premium Breaker Bar, 12 Inches Long, Nut Breaker Bar, 180-Degree Flex Cr-Mo Head with Cr-V Steel Construction : Amazon.ca: Tools & Home Improvement

www.amazon.ca

- EPAuto 1/2-Inch Drive Click Torque Wrench (10–150 ft-lb / 13.6–203.5 N·m) — $47.87

https://www.amazon.ca/gp/product/B01M1D17AW/ref=ox_sc_act_title_5?smid=A1L7F5DL4H71TK&th=1

- NECAMOCU 4-Pack Razor Blade Scraper (with 50 blades) — $13.98

NECAMOCU 4 Pack Razor Blade Scraper, Premium Cleaning Scraper Tool with 50PCS Metal & Plastic Razor Blades, Multi-Purpose Glass Scraper for Windows, Sticker, Adhesives, Decals, Cooktop, Paint Removal : Amazon.ca: Tools & Home Improvement

NECAMOCU 4 Pack Razor Blade Scraper, Premium Cleaning Scraper Tool with 50PCS Metal & Plastic Razor Blades, Multi-Purpose Glass Scraper for Windows, Sticker, Adhesives, Decals, Cooktop, Paint Removal : Amazon.ca: Tools & Home Improvement

www.amazon.ca

GASKETS & SETS
-(Gaskets I am still unsure of which one as I will probably need an exhaust manifold gasket and a riser gasket as well?)-

- Quicksilver 99777Q02 Exhaust Elbow Gasket (MerCruiser 3.0L) — $12.82

Quicksilver 99777Q02 Exhaust Elbow Gasket, Standard Cooling, MerCruiser, 3.0L : Amazon.ca: Sports & Outdoors

Quicksilver 99777Q02 Exhaust Elbow Gasket, Standard Cooling, MerCruiser, 3.0L : Amazon.ca: Sports & Outdoors

www.amazon.ca

- FEL-PRO 17200 Engine Cylinder Head Gasket Set — $105.51

FEL-PRO 17200 Engine Cylinder Head Gasket Set, Head Gasket Sets - Amazon Canada

FEL-PRO 17200 Engine Cylinder Head Gasket Set in Head Gasket Sets.

www.amazon.ca

- Sierra International 18-2946 Marine Head Gasket — $65.93

Sierra International 18-2946 Marine Head Gasket, Head - Amazon Canada

Sierra International 18-2946 Marine Head Gasket in Head.

www.amazon.ca

- MAHLE HS5719 Head Set — $136.45

MAHLE HS5719 Head Set, Head - Amazon Canada

MAHLE HS5719 Head Set in Head.

www.amazon.ca

 

[ESGWheel]

Its looks good. This is great pre-planning. But prior to getting the torque wrenches get the torque specs for your engine to make sure they are in the right range. On the low end will be things like the valve cover and riser to the manifold. High end will be the cyl head. Ideally torque wrenches are used in the 25% to 75% range, but not a hard and fast rule.

One note of caution prior to spending the money > we still do not know the extent of the damage. Certainly, we are all hoping for a simple blowen head gasket but what if the extent is much more. What if the motor needs to come out for a rebuild? Then an entire engine gasket set will be needed which will include the head gasket set.

 

[DanOnTheBoat]

Thanks ESGWheel! Hope it'll only need a head gasket...

I went with a MANHLE complete gasket kit. So I think I'm going to start tearing into the engine tomorrow. I've made sort of a "step by step" list for disassembly and reassembly.

1. Disassembly​

1. Prep
   • Disconnect battery.
   • Drain coolant (block drains + manifold).
   • Drain engine oil.
   • Label hoses & wires for easy reassembly.
   • Remove spark plugs.
2. Topside
   • Remove flame arrestor & carb/TKS unit.
   • Disconnect throttle linkage, fuel line, vacuum lines.
   • Remove exhaust manifold.
   • Remove valve cover.
3. Head Removal
   • Loosen rocker arms (keep pushrods in order).
   • Remove pushrods & lifters (if needed).
   • Remove intake/exhaust gaskets.
   • Loosen head bolts in reverse torque sequence (start outer → work inward).
   • Lift cylinder head.
4. Prep for Shop
   • Scrape block deck clean (razor blade OR gasket scraper, no gouging).
   • Chase head bolt holes with thread chaser.
   • Bag and tag parts.
   • Send head to machine shop: ask for cleaning, pressure test, and light resurface.

2. Reassembly​

1. Block Prep
   • Wipe block deck with brake cleaner/acetone.
   • Ensure absolutely clean, smooth, dry surface.
   • Check flatness with straightedge if possible (<0.003" warp).
2. Head Install
   • Place new head gasket (no sealant — it goes on dry).
   • Position head carefully on dowels.
   • Install new head bolts (lightly oil threads & under bolt heads).
3. Torque Specs – Cylinder Head Bolts
   (GM 3.0L, 10 bolts, torque-to-yield style)
   • Torque sequence: start center → spiral outward.
   • Final spec: 90 ft-lb (122 N·m)
   • Do in 3 passes:
     1. 30 ft-lb
     2. 60 ft-lb
     3. 90 ft-lb
4. Valve Train
   • Reinstall pushrods in same order.
   • Install rocker arms.
   • Adjust lash (hydraulic lifters: tighten until pushrod has zero play, then 1/2–3/4 turn more).
5. Intake/Exhaust
   • Install intake & exhaust manifold gaskets.
   • Torque intake manifold bolts: 25 ft-lb (34 N·m)
   • Torque exhaust manifold bolts: 33 ft-lb (45 N·m)
6. Valve Cover
   • Install gasket + cover. Torque bolts: 7–9 ft-lb (hand snug).
7. Cooling & Fuel
   • Reconnect hoses, carb/TKS unit, throttle linkage, wiring.
8. Fluids
   • Fresh oil & filter.

 

[ESGWheel]

Awesome step by step > I am going to copy that and save it!

Of note is that you may not need to take to machine shop > post those pics as suggested and then clean and then check for flatness. No issue if do, that is the safest route but is $$. The acetone will also work for checking for valve sealing.

 

[DanOnTheBoat]

Thanks lol.

Noted thanks. I will take it all apart and post pictures here.

Also, question about untightening the head bolts. I know that many videos dont show this and dont talk about this but is there a specific way to untighten them? I read that you have to do 1/4 - 1/2 turn for every bolt working your way from the outside bolts to inner bolts. Basically working your way around in a spiral until you get to the middle bolts, so they are all finger-loose.

Are new head bolts needed/must?

Also, what about the exhaust manifold? Do you have to do the same for that? Or can you unscrew the bolts and fully take them out one by one?

 

[kd4pbs]

Gaskets compress as they are tightened, which is why it is recommended to perform a certain tightening sequence. Since an installed gasket is compressed, there's no reason to follow a loosening sequence.
I'd buy new OEM bolts or some from a known good vendor such as ARP. One never knows how they may have been abused in the past unless you know the history of the engine from the factory.
In case you didn't know, here's a quick tip to know what order to set the lifter lash: turn the engine over until the rotor on the distributor is pointing at a spark plug terminal, then adjust that corresponding cylinder.

 

[DanOnTheBoat]

Gaskets compress as they are tightened, which is why it is recommended to perform a certain tightening sequence. Since an installed gasket is compressed, there's no reason to follow a loosening sequence.
I'd buy new OEM bolts or some from a known good vendor such as ARP. One never knows how they may have been abused in the past unless you know the history of the engine from the factory.
In case you didn't know, here's a quick tip to know what order to set the lifter lash: turn the engine over until the rotor on the distributor is pointing at a spark plug terminal, then adjust that corresponding cylinder.

Thanks for the advice kd, thats actually very helpful with tightening the lifters. Lifters meaning the Pushrod lifters?

About loosening head bolts, if I don't loosen the head bolts in a sequence and bit by bit won't the head crack? I'm afraid if I just start loosening them out of order the head will crack...

I did a lot of digging for head bolts and I found these:

Amazon.com: Head Bolt Set for 2.5L 153 & 3.0L 181 CID 4-Cylinder Marine Engines | High-Performance Replacement : Automotive

Buy Head Bolt Set for 2.5L 153 & 3.0L 181 CID 4-Cylinder Marine Engines | High-Performance Replacement: Head Bolt Sets - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com