What to do with a broken down 40 year old Detroit Diesel engine?
After pondering our options, we decided to give Interstate PowerSystems the go-ahead to pull Zephyr’s engine for a full dissection with intention to rebuild. We had grown comfortable with their expertise, openness, and professionalism – and felt that they were the right shop for the job.
“We can rebuild it. We have the technology. We can make it better than it was. Better…stronger…faster.” – The Six Million Dollar
But first we had to extract the engine from the bus…
Old time bus mechanics have told us how ‘back in the day’, a revenue generating bus shop could swap an engine out of a 4106 bus before lunch, and then do another in the afternoon. The entire engine cradle is attached to the bus by just four bolts (and a whole lot of hoses and wires!), and two technicians who knew exactly what they were doing could unhook the old engine, lower it onto a cart, and roll a ready replacement right in without even breaking a sweat.
Doing the same procedure on a bus that hasn’t been wrenched on in decades wasn’t quite so painless – but it still took well less than a day’s work to perform the extraction.
Anthony, the Interstate tech assigned to the disassembly, fought with old fittings that hadn’t been loosened in decades, and used colored wires to carefully mark every hose and wire for eventual reassembly. A few bolts needed to be cut away. None of us had first-hand experience disassembling a GM, but our original GM manual proved invaluable to help track down a few tricky details – such as realizing that the bumper came off as part of the engine cradle, and did not need to be removed separately.
Not having a GM4106 engine cart to drop the engine into and roll away, we made do with a forklift. A very big forklift!
And by late that afternoon, the engine was out!
Once extraction was complete, we dragged Zephyr back out to the parking lot for an extended stay, now complete with a back sun porch.
The engine meanwhile got treated to a spa day, steaming the accumulated decades of gunk off.
And then the disassembly began.
The past week has been hugely educational seeing our big engine stripped down piece by piece to just a bare block, relatively tiny in comparison. The tech responsible, Steve, has been fabulously meticulous – and he knows his way intimately around a 2-stroke.
First the Allison V730 transmission was separated and set aside.
Then the engine was hoisted from the fork lift and mounted on a stand
Then all the accessories mounted were removed – one at a time we watched the starter, alternator, blower, water pump, exhaust manifolds, oil pan, oil pump, and air compressor come off. The cylinder heads were carefully removed and set aside, in the process exposing the mechanics of the Jake brake, the engine timing ‘rack’, and the N70 injectors which spray the diesel into the cylinder.
Removing the cylinder sleeves and the pistons revealed signs of extreme heating (and even cracked liners) – but the heat damage was evident primarily on just the two centermost lower cylinders.
With the pistons removed, the engine could be flipped over so that the crankshaft could be inspected and removed for magna-fluxing and polishing.
Then the beautiful watch-like gearing at either end of the block could be extracted, and the two camshafts removed as well.
Finally – we were left with a bare block. Steve put it through an industrial washing machine, and has been cleaning, polishing, and inspecting every square inch of it to prepare it for rebuilding – working out the parts list of every little thing that needs to be rebuilt or replaced to make our engine as good as new.
It was an absolutely fascinating process, and we loved that the our rebuild tech Steve took the time to answer all of our questions and explain the inner-workings of every part of the engine.
This video slideshow gives you a taste of it all:
What we learned about what went wrong:
The goal of the disassembling the engine wasn’t just to prepare it for rebuilding, but to hopefully determine exactly what might have caused the problem in the first place… and repair anything that might have been our next awaiting problem.
We were able to rule out theories like the water pump spindle breaking, stopping coolant circulation. And the thermostats were a tiny bit crusty, but have tested as still functional and not sticking.
The things we discovered out of the ordinary during the dissection:
- The air filter (less than a year old and with just 4,062 miles on it) had blown out, and was partially sucked into the engine air intake.
- The two center cylinder liners on the lower bank showed signs of extreme heat and metal fatigue.
- The coolant hose to the air compressor was completely clogged – seemingly unrelated to the current issues (the air compressor was working fine), but discovering this and fixing it will save us from an air compressor failure someday down the road.
- The shaft for the oil pump was starting to wear out. It was far from failing, but catching this now saves us a major eventual problem. Finding these lurking future issues is exactly why we wanted to do a complete out of frame rebuild and not just the quickest possible repair.
Everything else inside the engine so far looks to be in good shape, other than typical wear-and-tear and age. So as of yet, we have not reached a definitive conclusions as to what malfunctioned to cause the overheat situation and damage in the first place.
All of the technicians here feel confident that the block is serviceable and a good foundation to rebuild on, and we’re rebuilding or replacing whatever else we can as preventive action.
We’ve been given a firm quote for the work, which came in less painful than anticipated… and now the rebuilding begins.
The alternator and starter have been sent out for overhaul, a new radiator core is being constructed complete with a new transmission cooler, and all the necessary engine parts have been ordered. All other pieces serving the engine are also being carefully inspected, cleaned and rebuilt/replaced as needed – from hoses, wiring, pumps, thermostats and more.
We’ll be installing remanufactured and warrantied heads, instead of cleaning up, testing and rebuilding the existing ones that may or may not have suffered damage in the overheat.
This coming week, we look forward to seeing it all going back together – a piece at a time.
A work of art. A jigsaw puzzle.
It will be fun to watch and learn. *grin*