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Tiara 4000 Express Cummins 6CTA 8.3 In-Frame Engine Rebuild
#1
I’ll start off by saying now is a great time to inspect and test your engine oil/temp alarms. I recently experienced an overheat event on my port engine at 2200 RPM with no indication other than the temperature gauge. By the time I had noticed it was at 210°F, the damage was already done. A failed hose clamp on a coolant line resulted with all the coolant in the bilge. There had been no loss of power when I shut it down. My engine temp alarm never sounded. I opened the engine hatch and immediately saw all the steam. Originally, I didn’t think it was going to be that bad. There was only a bit of discoloration on the turbo and the exhaust manifold immediately aft of it. I got back to the dock and then put everything back together the next day. All was great until I looked and saw all the steam coming from my port exhaust. You could smell the coolant. Damage included a cracked exhaust manifold, blown head gasket, piston ring expansion, and sleeve scoring. 

I’ve seen a few inquiries regarding an in-frame rebuild of the Cummins 6CTA 8.3 in the 4000 Express, so thought I would confirm it is indeed possible and actually pretty simple for a seasoned mechanic with the right tools. Here is my experience as well as a few photos. 

First, I’ll say I consider myself pretty good with a wrench, but I would never try tackling this job myself. I was fortunate to find Craig from Nordic Engine Works in Seattle who had obviously rebuilt the 6CTA dozens of times and didn’t mind having this owner working as his assistant. We started by pressure testing the coolant side and quickly found the exhaust manifold was cracked. Bubbles in the expansion tank were also observed with the engine running. The oil didn’t show any evidence of a milkshake but there was a few drops of coolant on the inside of the oil fill cap. We opted to pull the head for a closer look. This involved removing just about everything (heat exchanger, exhaust manifold, aftercooler, coolant tank, fuel lines, etc.) The head is pretty heavy and it did take both of us to get it onto the deck. Once removed, we noticed the vertical scarring over the cross hatching of the sleeves. Oh boy, here we go…

We took the head in to be rebuilt at a machine shop and sent the turbo and injectors in for testing. The next step was to drop the oil pan. The design to contain all the engine fluids directly under the engine prevented us from removing it fully but there was plenty of room for disconnecting the connecting rods from the crank. Once all the pistons were removed we pulled all of the sleeves. Next was cleaning…lots of cleaning, as well as surface prep and parts ordering. 

Now obviously I’m pretty disappointed taking on such a large nonbudgeted expense but being part of the rebuild process was actually pretty fun and very educational. We installed the new sleeves and dropped in the new pistons with new bearings on the existing connecting rods. (I learned there are serial numbers on both the upper and lower sections of connecting rods to keep them from getting mixed up) The oil pan was reinstalled with a new gasket. The rebuilt head was installed and torqued to factory specifications. Lifters, rockers, and valve adjustments followed along with installation of the injectors and fuel lines. Then came the new exhaust manifold, rebuilt turbo, heat exchanger, aftercooler, coolant tank, and all the miscellaneous hoses and piping. All in, my mechanic had under 30 hours on the boat. This obviously doesn’t account for his time for travel, part ordering, machine shop runs, etc., but I found it remarkable that a project like this could be completed in a week or two if everything is readily available. I’m happy to have had such a great experience after such an unfortunate one. 

Oh, and I installed a new engine alarm!  

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#2
Thanks for taking the time to post this! Great pictures and write up. If other things come to you about little tricks etc., please don't hesitate to add detail, I'm sure someone will find this very useful at some point!
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#3
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(01-27-2025, 08:18 AM)hiccup Wrote: Thanks for taking the time to post this!  Great pictures and write up.  If other things come to you about little tricks etc., please don't hesitate to add detail, I'm sure someone will find this very useful at some point!

I was impressed by my mechanic's use of a torch to remove stubborn bolts. There was no time wasted making several trips to apply penetrating oils or solvents, no broken bolts to extract, and no tapping was going to be necessary. Just slow and even heat for a minute or two and they came right out. Even the exhaust manifold bolts that hadn't been touched in 30 years were easily removed.

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Tiara 4000 Express Cummins 6CTA 8.3 In-Frame Engine Rebuild00