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| Trip Report [message #336403] |
Mon, 27 August 2018 00:50  |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma:
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Senior Member |
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Trip Report
Our agenda called for driving from the Twin Cities to Seattle via Bonneville salt flats in Utah. My friend Jim races a modified Suzuki motorcycle in land-speed record events, and this year he was hoping to exceed 200 mph! We departed the Twin Cities Saturday AM. I followed Jim in his Suburban and motorcycle trailer in tow. Jim wanted to make time so we were running 70-75 mph.
The first stop was in DeSoto, IA for gas. I filled with 27 gal of 87 octane E0 for 9.89 mpg. We noted that we were getting nearly the same mileage as Jim's suburban took 26.5 gal. I think my mileage was good because I was following Jim a little closer than I should have for a good portion of this segment! After the stop I noted that the A/F meter was running consistently richer, like 15% richer, dropping from an average of 15:1 down to 12.5:1 at cruising speeds. Also I noticed power was down a bit as well. What kind of awful fuel was this? After another 294 miles we stopped in Kearney, NE and filled up. The GMC took 42.1 gallons for 6.98 mpg, while Jim's Suburban was still getting 10 mpg! As I'm driving I'm thinking of scenarios that can cause the operation I'm seeing; rich air/fuel ratio and reduced power...it can't be fuel supply related; vapor lock, filters, pump problems would all lead to lean operation. A rich condition could be caused by carburetion, like a stuck choke or heavy float. It could be some sort of power reduction causing the engine to run at low vacuum (carb A/F control is strongly influenced by vacuum level). After another 315 miles we stopped for the night in Cheyenne. A possible cause for this low power and economy could be due to a timing chain that skipped a tooth on shutdown at that first gas stop. I recall it dieseled / ran-on for 2-3 cycles at that point, making a skip more likely. In the morning with a cold engine I aligned the crank balancer at TDC and checked the distributor rotor position. It should be about 10 BTDC where I set it last. The distributor was tight so it had not slipped. I pulled the cap off and the rotor was right on #1 or about 10 degrees retarded from where I set it. The cam gear has 36 teeth or 10 degrees per tooth. I think the timing chain jumped 1 tooth!
I immediately got out the Black List as I was concerned that any more tooth-jumping could cause the engine to stop running altogether or worse; several teeth out of time can bend valves and pushrods.
I found a willing Blacklister less than 50 miles away! Larry Coldren has shop space and GMC-specific tools! I put in 8 gal of Exxon 88 octane E10 and headed to Larry's shop. Larry graciously invited me and my GMC into his work space. It was Sunday so I began disassembly to verify if my theory was correct. First thing is the mechanical fuel pump, I pulled it off and reached inside. I rotated the crank back a bit and yes the chain was very loose. I stuck my phone to the hole and snapped a picture. I could see what appeared to be brown teeth between the chain links. A nylon cam gear? The coach is only showing 52k miles, so it's plausible that it has never been changed. The PO represented this coach as 44k original miles when I bought it in '13. Has anyone made it 152k miles with a nylon cam gear?
Time to pull it down. Off came the shroud, fan, belts, lower hose, water pump. We lifted the engine 2 inches to remove the front motor mount. That was the end of the day Sunday. Larry found a Cloyes timing chain set at an O'reillys only 20 miles away! First thing Monday I picked up all necessary parts and supplies for the job and pulled off the balancer and front cover. This confirmed not only a tooth out of time but a nylon cam gear and 3/4" slack on the chain! I'm lucky it made it as far as it did! The balancer was really hard to remove. A puller slowly pulled it an 1/8" at a time. We measured the "fit" and the crank nose was 1.500" while the balancer ID was 1.497". For reference the service manual calls out the spec at .001" interference to .0007" positive clearance. The Olds engine plant must have had a big press to get that balancer on! This could be trouble....Also while the balancer was off I checked the location of the TDC mark to verify if the balancer ring had moved at all. There is a reference in the service manual indicating the mark is indexed 16 degrees from the keyway and it checked good. I installed the new chain and gear set (note; a Cloyes c-3006k can be an OE style set - this one was not a double roller! This particular set has an aluminum cam gear but OE style chain). I reinstalled the front cover. The balancer reinstallation was being stubborn! We could only drive it on halfway with that interference fit. It's now late on Monday. We sought out the advice of a friend with a machine shop nearby. He machined the balancer ID down to 1.500" first thing on Tuesday. It then slipped on like a glove! I reinstalled the front cover, motor mount, water pump, hoses, belts, pulleys, fan and shroud. Added 2 gallons of Prestone, 2 gallons of distilled water. Drained and refilled the crankcase with Mobil1 15w-50 and a new filter. When the front cover is off you run the risk that debris can fall into the oil pan. I put a rag over the opening to minimize this but an oil change could not hurt. I fired it up and rechecked/set ignition timing at 10 BTDC and it was now about 7 pm Tuesday. I drove to the gas station and filled with 22.5 gal Valero 88 octane and I was off (this tank calculates out to 11.45 mpg probably due to babying it in for repair as well as a short fill) I departed with my sights set on Rawlins, WY 160 miles distant. I made it to Rawlins about 10pm, with no issues other than my dash lights quit about half way there! All exterior lights worked, as well as the dash telltales (turn indicators, high beam, brake). I assume the culprit is the headlight switch, but that fix will have to wait til I get home. Time to stop for the night. FYI Rawlins, WY is on a main east-west freight line. A train rumbles through every 30 minutes or so! At 6am I was up and headed for Salt Lake. I stopped in Rock Springs for gas, this time averaging 7.91, confirming the short fill on the last tank (my 2-tank average was 9.60 mpg). I stopped in Little America for a weight slip. 11000 lbs., 3780 front, 7220 rear. I picked up my spouse in Salt Lake City. She had flown directly to SLC and was able to see our friend go 215 mph, while I was stuck wrenching on the coach! Now we were driving with the generator on to run the roof air in 95F heat. We stopped in Snowville, UT for 35.6 gal of 89 octane Sinclair gas or 8.79 mpg. We drove to Ontario, OR and before stopping for the night added 27.2 gal Chevron 89 octane E10 for 10.48 mpg. We got up Thursday and headed for Seattle. We made an intermediate stop in Pendleton, OR to visit the Pendleton Woolen Mill. We got 14.0 gal of fuel at Ellensburg, WA, just enough to get home, and be at a low tank level on arrival as I wanted to run as much E10 out of the tank as possible. I can buy E0 locally which I prefer for any period when the vehicle will be unused. Once home I filled with 46.9 gal of Union76 89 octane E0, for a segment mpg of 10.3. This allows a total trip calculation of 2276 miles / 258.8 gal or 8.79 mpg. Not bad considering the 1-2 tanks at 7 mpg before the repair, some running at 70-75 mph and approx 10 hours of generator operation. I made it in one piece and only a 2 1/2 day unplanned side trip!
I can't say enough about the black list, the GMC community and Larry Coldren in particular! Larry was an absolute gentleman and gracious host. He had every tool imaginable which allowed me to make a speedy and proper repair. Thanks again Larry!
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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