Reply
 
Thread Tools Search this Thread Display Modes
 
Old 07-10-2017, 01:03 PM   #1
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Problems with NOS Cummins 6bta

Long story, but I can use help.

I have a Cummins 6bta, 250 hp. 1990 cpl 1241. The motor was never in service, and I bought it last fall to replace my ailing 6bt. Kept the same transmission and drive train from my 210 hp bt with the intent to deliberately have the boat underpropped.

In preparation for service I did a few basic things. I don't have a shop or good work space, so it was pretty cursory, but all looked good. Motor barred over smoothly, everything nice and clean.
- changed fluids
- replaced some hoses and front seal
- checked valve lash
- new impeller

I pulled the old motor myself, sold it, and put new seals in the old VD 72 transmission which I kept. Also put in a flexible torque adaptor plate. Bolted it all together and installed in the boat.

After launch the motor wasn't getting fuel to the injectors and wouldn't start. Not completely unexpected. So pulled the rotary pump and all injectors and lines and visited the local injection shop. They cleaned the pump and lines. Said there was rust in the pump but seemed confident they had remediated it. Injectors tested fine but the tips had pitting corrosion so replaced the tips. This was a bit unexpected and got me concerned about the internals... Motor had been run on the bench for an hour or two years earlier, and I had visions of nasty deposits left for a long time causing corrosion. No I put some ATF in the cylinders while I had the injectors out thinking it might help free up rings if they had corrosion as well. I also replaced the lift pump.

After getting the motor running - lots of smoke at first from the ATF - I was planning to break it in as a new motor. But a few other issues came up with fuel delivery and guages. I ran the motor for a few hours under light load, 1200-1500 rpm, and had what seemed like fuel starvation issues at higher power. I should also say that the motor was very difficult to start cold. I attributed this also to possible fuel supply issues. Had a mechanical oil pressure guage in the ER that showed good pressure from the first start.

Finally got the fuel system in good order and turned my focus back to the motor. Went out for a few hours. Couldn't get above about 2000 rpm, light white smoke, nothing too alarming until oil pressure started dropping gradually and oil and smoke started coming out of my CCV system. Checked oil and found it up by a lot, limped back in at low speed.

Back to the shop with the fuel pump. Assured that no leak in the shaft seal and fuel delivery specs are correct. Checked new lift pump for weeping fuel, none observed.

At this point my amateur diagnosis was that I had unseated rings, low compression, and incomplete ignition, and that unburnt fuel was washing into the crankcase.

Changed the oil, went out again to try to run the motor hard. I was pretty nervous about fuel dilution of oil and didn't stay out more than two hours total. Even then I was coming back with oil level up by a couple of quarts. I was trying to vary throttle between bursts of WOT and 1500-1700 rpm, still couldn't get above about 2000. I did this twice.

I did see some changes. Started getting grey smoke, then black at WOT. Along with the black smoke came what looked like oil out of the exhaust. White smoke seemed less at lower throttle. Had fuel in the exhaust all along.

After the second day of this I noticed that the paint on the exhaust manifold was heat discolored on all but the front cylinder. Pulled that injector and noticed that the nut came loose very easily, and the injector tip was wet and looked like new, no sign of ignition. I sprayed some Seafoam Creep into the cylinder, left it for a couple of days, and checked the torque on all the other injectors. They were fine. Not sure what happened with this one, but I think the injector wasn't seated properly when I reinstalled the injectors.

Changed the oil again and was out yesterday. Behavior is similar, but no more oil in exhaust, and the rate of fuel being dumped into the crankcase seems to be much less.

So, current state:
- motor still doesn't want to start cold without a good shot of starter fluid
- lots of blowby. I disconnected my CCV and essentially smoke comes out of the breather vent at a high rate all the time.
- not able to get above about 2000 rpm. Heavy black smoke at WOT, white smoke the rest of the time, some blue at startup/idle.
- as noted fuel dilution is occurring, but at a lesser rate than earlier.
- seems to be firing on all cylinders most of the time.

I now have about 20 hours run time. Temperatures have been unremarkable. I have boost and EGT guages new this year, and see 10-15 pounds of boost at WOT (1900 - 2000 rpm) so don't think there is a turbo issue. Max EGT I have seen is about 940.

My theory is still that I have a problem with seating the piston rings, but throw this out for debate. Are there other likely possibilities? Have I missed something in my DIY approach and diagnoses? Assuming that this is the case is there something else I can do short of a major disassembly? Right now I'm reluctant to keep doing what I've been doing. I now have a couple of barrels of dirty oil :-) Am considering pulling all the injectors and dumping some top end cleaner in the cylinders to soak for a few days in hopes of freeing up what I suspect are rings that are frozen in the piston.

I should also add that I am most definitely not overpropped, and there are no issues with throttle linkage or anything like that. Motor gets to full rpm in neutral, and I even got up to about 2200 in reverse yesterday.

Thanks in advance for any and all advice/commentary.

Jeff
__________________
Advertisement

Jeff F is offline   Reply With Quote
Old 07-10-2017, 01:15 PM   #2
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,311
Does sound like stuck rings. With engine idling and oil fill cap off, see if blowby is puffing in sync with one cylinder firing. If no paint cook on #1 exh port, that may be the problem hole. Can also crack injector fuel line nut and see if there is any change in rpm or exhaust smoke.

Can you post a vid with audio at idle with oil fill cap off?

High blowby is almost always rings. Might have gotten some corrosion in bore and on startup that stuck the rings.
__________________

Ski in NC is offline   Reply With Quote
Old 07-10-2017, 02:04 PM   #3
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Hope the video come through. Have cracked injectors and all cylinders seem to be firing. There is now some heat discolouration on #1 after my fix as well. Thanks for your help on this.
Jeff F is offline   Reply With Quote
Old 07-10-2017, 02:06 PM   #4
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Take 2 on video
Jeff F is offline   Reply With Quote
Old 07-10-2017, 02:11 PM   #5
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
https://youtu.be/bIsgbpQ2Nyo
Jeff F is offline   Reply With Quote
Old 07-10-2017, 03:00 PM   #6
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 4,891
If the rings are stuck, would it show on a compression test? I would think it would, and be a means of confirmation about what's happening.
__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Old 07-10-2017, 03:26 PM   #7
Guru
 
seasalt007's Avatar
 
City: Punta Gorda, FL
Country: U.S.
Vessel Name: Aweigh
Vessel Model: Nordic Tug 42
Join Date: Jun 2014
Posts: 628
Marvel Mystery Oil is what I would pour in for stuck rings. If some of them are broken, however, that is an entirely different kettle of carp.

Years ago I bought a 1960 MGA with the same symptoms. When I pulled the pistons the rings fell apart on the floor.
seasalt007 is offline   Reply With Quote
Old 07-10-2017, 03:48 PM   #8
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,311
That is a BUNCH of blowby. Not a happy engine.
Ski in NC is offline   Reply With Quote
Old 07-11-2017, 09:08 PM   #9
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Talked to seller, he had a motor shop do a thorough inspection last summer, said they had heads off and all was perfect. Motor was well sealed up when I got it.

I'm going to check the front gears tomorrow to make sure injection timing is correct. Seems like that would account for poor starting, fuel washdown, white smoke and poor power, and may have prevented rings from seating properly.

Thanks for your comments.
Jeff F is offline   Reply With Quote
Old 07-12-2017, 01:13 AM   #10
Guru
 
Xsbank's Avatar
 
City: Pender Harbour, BC
Country: Canada
Vessel Name: Gwaii Haanas
Vessel Model: Vancouver Shipyards Custom Aluminum 52
Join Date: Sep 2013
Posts: 3,213
Cummins are famous for blowby, I wouldn't give up yet. What I would be wary of is a runaway; have a way to block the air intake near at hand until you can get the fuel issue sorted. If its not your fuel timing, check that the tank return line is free and clear, check the air filter is too. Starting could be the air supply and perhaps even the heat coils aren't working. The 6CTA doesn't need them but the B might?

Break a leg...
__________________
Don't believe everything that you think.
What are we offended about today?
Xsbank is offline   Reply With Quote
Old 07-12-2017, 08:37 AM   #11
Guru
 
jleonard's Avatar
 
Join Date: Jun 2008
Posts: 3,459
Quote:
Originally Posted by Xsbank View Post
Starting could be the air supply and perhaps even the heat coils aren't working. The 6CTA doesn't need them but the B might?

Break a leg...
A Cummins B should easily start at any temp above freezing without the heaters (even lower). I had a couple of them.
__________________
Jay Leonard
Attitude Adjustment
40 Albin
Mystic,Ct. /New Port Richey,Fl
jleonard is offline   Reply With Quote
Old 07-12-2017, 09:59 AM   #12
Moderator Emeritus
 
ksanders's Avatar
 
City: SEWARD ALASKA
Country: USA
Vessel Name: LISAS WAY
Vessel Model: BAYLINER 4788
Join Date: Feb 2011
Posts: 4,410
Good luck!.

High blowby is symptomatic of internal engine failure of the rings Vs the cylinder walls.

Hard starting, inability to make full power, fule diluting oil, smoke, are other symptoms of a cylinder or cylinders that have failed.

Unfortunately the 5.9L cummins is not an engine that can be rebuilt internally in place. This is most likely going to require removal and tear down.
__________________
Kevin Sanders
Bayliner 4788
Seward, Alaska
ksanders is offline   Reply With Quote
Old 07-12-2017, 10:08 AM   #13
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 8,020
Quote:
Originally Posted by Jeff F View Post
Talked to seller, he had a motor shop do a thorough inspection last summer, said they had heads off and all was perfect. Motor was well sealed up when I got it
Did they run the engine on a stand or dyno?
sunchaser is offline   Reply With Quote
Old 07-12-2017, 10:33 AM   #14
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,311
I'm starting to doubt that is a NOS engine. Seems to run more like a clapped out high hour takeout from a sportfish. How sure are you of the history of the engine?

I have been around lots of engines that sat for years and unless moisture got in a hole and rusted things up, pistons, rings and liners usually are fine.

Often on B's with high blowby, the cylinder bores are not worn much and a quick hone to re-establish cross-hatch and new rings can get it back into good shape.
Ski in NC is offline   Reply With Quote
Old 07-12-2017, 06:47 PM   #15
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Now have a root cause analysis. I was assuming that problems were compression related, but it turns out the camshaft is out of time. So most of my run time has been with the cam and IP synched with each other but out of time with the crankshaft.

I omitted one piece of the story earlier, mostly out of embarrassment but also because I didn't see how it fit in the overall narrative. After I reinstalled the IP the first time and got the motor running there were some pretty awful noises from the front gears after a few hours of running. While I was taking the gear cover off I caught a glimpse of what looked like a bright shiny nut, but it disappeared when I got the cover completely off. Must have gone down the oil drain. There was damage to the cover, the case, and one very small chip in the edge of the camshaft gear. Could see where the object had bounced around the IP gear then made its way down to the camshaft gear and rattled around there. Did an inventory, and no bolts or pins missing from inside the case, so I came to the conclusion that I must have somehow dropped something in when I had the IP out the first time. Put a new cover and gasket on and moved on. It appears that this trauma is what threw the cam timing. There are accounts of this happening in Dodge trucks when the Killer Dowel Pin comes loose.

I should say that I'm at anchor out in the middle of nowhere, still hoping I can resolve this myself without finding a port and hauling the motor. Big question is whether there is a reasonable chance that I can come to a full resolution without doing this. I'm very patient and perseverent and don't mind figuring things out as I go, and am secure and self-sufficient here. I'm hopeful that with proper ignition and full power I can get the rings to set and solve the blowby.

To resolve, I think I need to
a) remove the cam gear, either with a really good puller or by removing the shaft through a hole cut in the bulkhead and having it pressed out. My preference is for the former, but need to find a puller and confirm clearances. Reinstall and retiming seems simple enough. I have an oven to heat the gear.
b) make sure no damage to valves or pushrods. Guess I'd need to pull the head to be sure.
c) change the oil again
d) get underway and load things up.

I should also add that I got a more detailed account of the motor history. It was never installed. When the owner was getting it ready to sell he checked it carefully, ran it, and discovered there had been a leak in the aftercooler core. He replaced the core, and fearing damage to the internals he had it sent to a shop. I have an invoice from 2016 showing complete disassembly, cleaning, and checking against tolerances, including new rings, gaskets and head bolts. Seller wanted to sell the motor in perfect shape and is a straight shooter, and I'm confident that the issues I've had apart from the dirty IP are all of my own doing.

Will post progress. Comments/advice will be read with interest!
Jeff F is offline   Reply With Quote
Old 07-13-2017, 01:36 AM   #16
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
I'll try to include some photos where I can. Here's the original gear cover that got mangled by the unidentified foreign object

Click image for larger version

Name:	ForumRunner_20170713_022031.jpg
Views:	82
Size:	43.5 KB
ID:	66691

It was actually punctured slightly in the area where the object got seriously caught in the camshaft gear.

When I took this off I was anchored out in Long Point on Lake Erie. No car. Not much in the way of local services, a decent grocery store is a 45 minute drive away. Local boat people don't do diesel. But as it turns out there's a one-man Dodge Cummins used parts operation about 15 miles up the road. Has an eBay store and ships all over. I called him in the morning, and he delivered a freshly painted cover to me that afternoon. He drove down to meet me at a bridge over a creek that I dinghied into :-) I had a spare gasket and crank seal in my onboard bin. Less than a day of forced downtime.

If there's one really compelling case for the old BT this is it.
Jeff F is offline   Reply With Quote
Old 07-13-2017, 01:41 AM   #17
Guru
 
Xsbank's Avatar
 
City: Pender Harbour, BC
Country: Canada
Vessel Name: Gwaii Haanas
Vessel Model: Vancouver Shipyards Custom Aluminum 52
Join Date: Sep 2013
Posts: 3,213
I can't see how you could possibly change the camshaft timing without something breaking, even with a nut rattling in there. How can it possibly jump a tooth? Are you sure its out?
__________________
Don't believe everything that you think.
What are we offended about today?
Xsbank is offline   Reply With Quote
Old 07-13-2017, 01:57 AM   #18
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Quote:
Originally Posted by Xsbank View Post
I can't see how you could possibly change the camshaft timing without something breaking, even with a nut rattling in there. How can it possibly jump a tooth? Are you sure its out?
It didn't jump a tooth. I had checked all that when I replaced the cover. The camshaft gear is driven by the driveshaft and then drives the IP. And the common TDC reference is based on the camshaft gear position. But the gear goes on the camshaft with a press fit. Not normally ever adjusted or changed outside of a major overhaul. It's that press fit connection that allowed the cam timing to change. There was some rotation between the shaft and the gear caused by the nut getting briefly caught up between the gear and housing. Hard to imagine - rotational inertia on the shaft? - but well documented in the pickup world.

I determined it was out by looking at the valve positions when locked at TDC. Knew exactly what to expect because I had checked this just before I installed the motor. Also have full shop manuals, and the Dodge pickup boys have broken everything than can possibly be broken on these motors. The valve positions now are not at TDC, and this is the only possibility.
Jeff F is offline   Reply With Quote
Old 07-13-2017, 02:32 AM   #19
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Quote:
Originally Posted by sunchaser View Post

Did they run the engine on a stand or dyno?
They ran but not under load.
Jeff F is offline   Reply With Quote
Old 07-13-2017, 03:07 AM   #20
Guru
 
Jeff F's Avatar
 
City: Great Lakes
Country: Canada
Vessel Name: Mazurka
Vessel Model: Mainship 34 Original
Join Date: Nov 2015
Posts: 595
Quote:
Originally Posted by Jeff F View Post

It didn't jump a tooth. I had checked all that when I replaced the cover. The camshaft gear is driven by the driveshaft and then drives the IP. And the common TDC reference is based on the camshaft gear position. But the gear goes on the camshaft with a press fit. Not normally ever adjusted or changed outside of a major overhaul. It's that press fit connection that allowed the cam timing to change. There was some rotation between the shaft and the gear caused by the nut getting briefly caught up between the gear and housing. Hard to imagine - rotational inertia on the shaft? - but well documented in the pickup world.

I determined it was out by looking at the valve positions when locked at TDC. Knew exactly what to expect because I had checked this just before I installed the motor. Also have full shop manuals, and the Dodge pickup boys have broken everything than can possibly be broken on these motors. The valve positions now are not at TDC, and this is the only possibility.
I'm making some of this on the fly here and much of my research has put me in the non-marine world which can be dangerous. Just reread the service manual and they say it's a keyed connection. So maybe I'm all wrong here. But the valves definitely don't line up against pinned TDC, and I'm sure they did before. What could have happened? Time to sleep on it.
__________________

Jeff F is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 12:15 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×