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Old 11-12-2021, 05:59 PM
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Pressure Drop All Cylinders?

I asked this in a facebook forum and got some interesting answers but want your input:

Any ideas why all four cylinders would drop in pressure when tested cold? Previously had a solid 120 but now all cylinders read right around 60.
I brought the boat out of winter with great success but the other day on a long sail coming out of an inlet it started dying as the boat pitched with the waves. I suspected back pressure since the exhaust was plunged under the water with those waves. Had a few runs where the engine died with little indication of why. Dying when at idle was particularly repeatable. The next morning, the engine had a lot of difficulty starting. Cleaned off some very sooty spark plugs when it sounded like I had a misfire. Compression test of all cylinders and spark test sat but the pressure in all four was about 60psi.
Fuel level was almost full.
Eventually I got her running and got out of the marina confidently on flat water with throttle.
Thoughts?
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Old 11-12-2021, 06:16 PM
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Dirty Fuel

Pitching in big waves brings to mind stirring up muck lying in the bottom of your fuel tank. Take a look at your in line fuel filter and also drain the carb bowl and see what comes out. If there is a lot of foreign debris, a thorough carb cleaning is in order.

Tom
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Old 11-12-2021, 06:32 PM
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Quote:
Originally Posted by indigo View Post
Pitching in big waves brings to mind stirring up muck lying in the bottom of your fuel tank. Take a look at your in line fuel filter and also drain the carb bowl and see what comes out. If there is a lot of foreign debris, a thorough carb cleaning is in order.

Tom
Will do.
Is there a way to check the polishing filter?
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Old 11-12-2021, 07:14 PM
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What kind of fuel filtering do you have inline? (Tank to Carb)
What kind of fuel pump? (Manual or Electric)
Do you have a fuel pressure gauge by chance?
Agree it could easily be stirred up crud.
As Tom said a quick look at what comes out of the carb would help tell you.

Lastly, might be worth taking a look at your oil and see if it's milky or the level has gotten higher.

Is the engine running well now or still hard starting/running?
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Old 11-12-2021, 09:15 PM
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I take it you're talking about cylinder compression. Before you get excited, try it with a different gauge.
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Old 11-12-2021, 10:11 PM
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Quote:
Originally Posted by roadnsky View Post
What kind of fuel filtering do you have inline? (Tank to Carb)
What kind of fuel pump? (Manual or Electric)
Do you have a fuel pressure gauge by chance?
Agree it could easily be stirred up crud.
As Tom said a quick look at what comes out of the carb would help tell you.

Lastly, might be worth taking a look at your oil and see if it's milky or the level has gotten higher.

Is the engine running well now or still hard starting/running?
Ah sorry. Electric fuel pump, no fuel pressure gauge. I have the Racor fuel water separator and the in line polishing filter from Moyer.
I haven't been able to troubleshoot further because it's been hauled out and the marina isn't big on running the engine. I can disconnect the fuel pump and dry start to get the pressure at some point so I'll try and do the alternate pressure gauge.
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Old 11-13-2021, 03:03 AM
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Quote:
Originally Posted by Jo Ross View Post
Is there a way to check the polishing filter?
Yes, it would be great if the polishing filter stopped the (alleged) crud from entering the carb.
The only way to "check" the polishing filter if you don't have a fuel pressure gauge after it before the carb is to remove it.

ex TRUE GRIT
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Old 11-13-2021, 09:37 AM
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How did you conduct the 2 compression tests?

The test should be done first dry and then with some oil sprayed into the cylinder the wet test.

When conducting the tests the throttle and choke should be set at wide open, all plugs removed and the batteries topped off. Use the same gage and you are looking for how close the values are to each other from cylinder to cylinder.

Did you adjust the valves and double check for "crank position" to be sure you were on the heel of the cam?

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Old 11-13-2021, 04:10 PM
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Quote:
Originally Posted by Jo Ross View Post
I asked this in a facebook forum and got some interesting answers but want your input:

Any ideas why all four cylinders would drop in pressure when tested cold? Previously had a solid 120 but now all cylinders read right around 60.
I brought the boat out of winter with great success but the other day on a long sail coming out of an inlet it started dying as the boat pitched with the waves. I suspected back pressure since the exhaust was plunged under the water with those waves. Had a few runs where the engine died with little indication of why. Dying when at idle was particularly repeatable. The next morning, the engine had a lot of difficulty starting. Cleaned off some very sooty spark plugs when it sounded like I had a misfire. Compression test of all cylinders and spark test sat but the pressure in all four was about 60psi.
Fuel level was almost full.
Eventually I got her running and got out of the marina confidently on flat water with throttle.
Thoughts?
I have a Tartan 34 with side exhaust. The exhaust is often underwater and
presents little problem with back pressure. Of course it has the Tartan standpipe exhaust which prevents waves enterng the exhaust.

best Art
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Old 11-14-2021, 10:09 PM
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The standpipe with the side exhaust works so well on the T30 and T34 that I'm surprised other boats aren't converting to it.
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Old 11-14-2021, 10:45 PM
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Quote:
Originally Posted by ArtJ View Post
I have a Tartan 34 with side exhaust. The exhaust is often underwater and presents little problem with back pressure.
From a discussion 12 years ago:
https://www.moyermarineforum.com/for...17&postcount=8
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Old 11-30-2021, 10:01 PM
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I think it's the head gasket

After a few more surveys I'm thinking it's a blown head gasket where there's opening between the cylinders. That would make sense for the common 60 psi pressure between the cylinders. If I remember right, I checked the pressure with a single spark plug removed at a time which would prevent it from going to zero. I'll try and verify that the next time I'm out there but I have a feeling it's going to be a long hard battle of getting that thing replaced.
Ugh...
Thoughts?
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Old 12-01-2021, 08:59 AM
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I always do compression tests with all 4 plugs out.
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Old 12-13-2021, 07:05 PM
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New Head Studs?

I just noticed Moyer's been sold out for a while. Any thoughts on buying replacements for the studs when I pull the head off?
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Old 12-15-2021, 12:49 PM
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Alright, here she is.

So, I'm all good with the head. Came off no problems.

Going to start scraping off the old head and cleaning everything. The manual says wood chisel? Is that a good idea? Currently soaking in PB Blaster and I'm going to get a scraper.

Moyer Marine is out of head studs and I would like to replace them since the stud puller does a number on the threads.
Can someone either point me to a comparable source or give me the specifications to simply have them made?

Any other pointers welcome. Thanks, ya'll.
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Old 12-15-2021, 03:06 PM
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I have got studs before at auto parts stores and hardware stores.
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Old 12-15-2021, 05:21 PM
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Old 12-15-2021, 11:39 PM
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Jo, I think I saw this same post over on the C-30 or A4 FB forum. It reminded me I have a nice plastic "chisel" I would start with, and personally, I would shift to metal razor blades after that, or even the plastic razor blades I've come to appreciate in recent years.

Sorry, no input on the studs except that let's hope you are getting them reliably enough to equal what Moyer's offered. My only comment here being that Moyer always makes sure the stuff they sell fits. Unfortunately, it seems like the global supply chain issues have crept into our little niche motor.

-edit - another option is to remove the old studs to see if they fit the bill for re-use. You can put two nuts on a stud and cinch them together with two wrenches, and then try to remove the stud cleanly with one wrench, and inspect it for re-use. I have a project A4 in my little shop that only turns about 130° rotation, and I suspect I will need to employ this technique after I pull the head to unfreeze the crank.
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Old 12-17-2021, 12:58 AM
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Valve seating?

Thanks for y'all's input. I'm making headway.

I'm looking at my valves now that I've cleaned things up and I don't get the warm fuzzy feeling that they're seating correctly. There is definitely buildup visible when they raise and I'm afraid to touch them because of all the warnings about being careful scraping near them.

Any thoughts on what to do here to make sure there's a good seal and not too much buildup?
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Old 12-17-2021, 03:06 AM
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Quote:
Originally Posted by Jo Ross View Post
Thanks for y'all's input. I'm making headway.

I'm looking at my valves now that I've cleaned things up and I don't get the warm fuzzy feeling that they're seating correctly. There is definitely buildup visible when they raise and I'm afraid to touch them because of all the warnings about being careful scraping near them.

Any thoughts on what to do here to make sure there's a good seal and not too much buildup?
If you believe your valves are not seating properly, it is a no brainer: take them out!!! you have done 95% of the job here, just finish it by removing the valves. It is not that complicated: once out, you will be able to clean the buildup on those valves in no time. Then a quick lap on the seat, and you will be able to eliminate the valves as a source of the lack of compression. just be thorough, block the 2 holes in the "valve compartment" to prevent pieces from falling in the oil sump, and catch all lapping compound etc..
There are a few tricks to be able to do a valve removal in 10 minutes rather than 3 hours, do not ask me how I know this (https://www.moyermarineforum.com/for...t=11241&page=3)

Good luck. By the way, it is a very satisfaying job to do...
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Old 12-17-2021, 10:36 PM
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Oh boy...

Man, I really do not want to do that... there is not a lot of room between the valve galley and the wall. I agree, I've done almost everything that would be required to prep but... ugh...

I need a better tutorial before I'm confident enough to do that. Where's the best spot to get one of those tools?
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Old 12-19-2021, 10:36 AM
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Alright, I'm going for it.

So, my inner demons got the better of me and I'm going to pull the valves and clean/lap them.
Ordering the tool from Moyer.
I've got the overhaul manual in the boat (not in front of me) so forgive me if these questions are answered in there but:

I've heard replacing springs may be required but I'm not sure how to tell if they need it.
Are the valve keepers something I should anticipate replacing?
What is the valve reamer tool for? If my valves are operating correctly it doesn't seem like the path is a problem and therefore I don't need it, right?

- Jo
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Old 12-19-2021, 12:29 PM
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OK, I've been watching the progression in this thread for over a month so here are a few observations:
  1. A blown head gasket was assumed in post #12 so the head was removed. No follow up on the condition of the head gasket though. Was there any evidence of a head gasket problem? Previous compression testing did not (to me) indicate a head gasket problem.
  2. Now we're chasing down valves. As in the prior comment, previous compression testing did not (to me) indicate a valve problem.
  3. About the previous compression test, going from 120 on all four cylinders to 60 on all cylinders suggests testing equipment and technique to me and I'm not alone, see post #8. Was the compression test repeated following Dave's advice prior to head removal? I do not remember reading that is was.
  4. The original problem was poor running and shut down in rough conditions indicating a fuel contamination problem (posts #2, 4 and 7) yet we seem to be chasing a completely different path. I did not read where fuel contamination was either confirmed or eliminated. To emphasize, the original symptom points directly to it.
  5. Other than time and money investments there is no downside to cleaning up the block and head, replacing the head gaskets (2 of them) and spiffing up the valves but my concern for you at this point is after all that has been done there's a chance you'll still have contaminated fuel and a repeat of the original problem.

edit: Reasoning for the above
For the compression loss to be even across all four cylinders due to either the head gasket or valves, all cylinders would have to be affected exactly the same. That just doesn't happen with valves and for such a total head gasket failure to occur with no water in the cylinders or oil, no way.
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Last edited by ndutton; 12-19-2021 at 01:03 PM.
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Old 12-19-2021, 09:57 PM
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Spot on

You're not wrong on any count.
I'm hauled out and they are pretty adamant about not running the engine on the hard so I did what I could on the water in short time.
I agree at this point that the head gasket was not the culprit, but these valves are worryingly blocked, whether that lends to the compression issues or not.
As for the fuel, it's a very likely cause. The main separator had considerable sediment in the bottom. I'm not sure how to go about checking the fuel tank yet but the churn we were in that led to the rough running would definitely have stirred up the bottom. We went through a few cans so in my mind we were running on fully fresh fuel.
Also, all of this carbon buildup makes me think I'm perhaps running lean? Carb is getting a cleaning and I'll check for sediment in there too.
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Last edited by Jo Ross; 12-20-2021 at 08:46 AM. Reason: Add photo
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