Friday, January 14, 2022

When BIG BANGS are not just a theory…

Some rather grisly engine blow-ups have come my way in the past few months and each one was unique in its own way.

First, a “Restored” CL77 305 Scrambler came down from LA because “I can’t get it started” and he thought that I could get it going for him on a “Drive-by” repair stop. I try my best to get small-ish bike repairs turned back around in a few hours, if at all possible. It’s a 3-5 hour round trip from Temecula, the OC, and much of LA, so it is a real commitment to bring a bike down for me to peer into and hopefully get squared away in one trip.

The CL77 was picked up in WA state off of a Craigslist posting by the current owner who was visiting his daughter up North. The seller was a “car restoration guy” who loved the looks of the 305 Scramblers and wanted to restore one. When it arrived, it was evident that a lot of work had gone into the bike, cosmetically, but the mechanical status was unclear. So, the first test is a compression test to see if we have some kind of foundation to build from. In this case, the left side was 175psi and the right side was reading 60 psi! The next step is to adjust the valves and cam timing to see if the compression readings will come up, due to a leaking/sticking valve, perhaps.

The battery was charged enough to make the bike run, but given the previous attempts by the owner, I guessed that the pilot (idle jets) were probably plugged up. For those in the know, working on the carburetors on a 250-305 Scrambler are a real PIA due to the right side proximity to the exhaust system. Clearing the right side carb idle jet was relatively easy and necessary due to a plugged-up #38 jet hole. Sometimes, you can reach under the right side carburetor with the transmission cover removed and pop the left side float bowl off to access the jets. Getting a short, slender screwdriver up inside the well for the pilot jet is always taxing and often you wind up having to remove the carb in order to get clear access to the jet. And in this case, the carb needed to be removed, which entails loosening the whole exhaust system, then easing the left air cleaner cover off, to allow access to the little short 6mm bolts that hold the filter to the mounting brackets.

With bolts removed, the air filter tube must be loosened from the carb inlet and the whole assembly set aside. Then, with just the right 10mm wrenches, the two mounting nuts can be removed allowing the carb to be pulled off of the studs and turned to give access to the jets. Sure enough, the pilot jet on the left carb was plugged up, too. Removing the carb from the cylinder head opens up more issues concerning flattened out o-rings on the carb flange and insulator, plus often the float bowl gasket expands if exposed to alcohol-based gasoline making reassembly impossible without replacing the old gasket with a new spare or sometimes washing the old gasket in hot, soapy water and then giving a bit of sunlight or a heat gun treatment to drive out the alcohol from the rubber gaskets. With the bowl off it is a good idea to check the float level settings, as I have seen many, many carbs with reversed float level settings. The float level mantra for 250-305s is “26mm carbs get 22.5mm float levels and 22mm carbs get 26.5mm float levels”

Once everything was checked over and reinstalled the bike started up on the second kick I did recheck the ignition timing statically before starting it up and then always recheck it with a dynamic timing light when the engine is running to determine if the spark advancer mechanism is working or worn/broken.

The second kick startup was a nice surprise, however, the breather tube which was pointed out to the right side yielded a constant stream of blue smoke due to oil burning. The owner took one look and said, “Can you fix it, please?” I agreed and by the time the owner had returned to LA I had the engine out of the chassis and on the workbench for a peek into the top end. When the cylinder head came off, there was a noticeable notch in the top outer edge of the right side piston. When the cylinders were removed a large burned-through spot on the piston crown extended all the way down past the piston rings. That must have made a noise when it let loose. The head gasket fire ring was burned through as well, so something caused enough detonation long enough to torch the piston crown and head gasket at the same time. These are rather unusual events. Pistons often seize first before they get burned through the tops and the burn area is often in the middle of the piston crown, rather than down one edge.

In any case, the cylinders got a re-bore and some .50 oversized pistons, plus a set of new valves. When the owner came back he was delighted to find that the bike would start up on a couple of kicks and no longer spouted blue smoke and droplets out the breather tube. One down and more to go…

The second bike was also a CL72, which came down from LA, as well. I had briefly looked at the bike’s condition on a return run from Vegas after the Mecum auction. I transported my purchase and a 1962 CB72 for my friend on the way back home to San Diego. He mentioned that the CL72 had been a daily driver for a couple of years, then one day while cruising along at moderate speeds the bike suddenly went BANG and quit instantly. I did a few quick checks on the engine and discovered a tight exhaust valve. I backed off the adjuster quite away until it had more than enough clearance, then tried to kick-start it. BANG again! No more time to spend on a dead Scrambler, so it was left behind while I finished the trek back to San Diego.

Fast forward a year and a half… the bike and owner came down to resolve the engine problem. He helped me extract the engine from the chassis and put the engine up on the workbench. After removal of the cylinder head, we noticed a mangled right-side piston and a broken sleeve flange. Lots of metal and damage to the cylinder liner and the piston, but not too much else took a hit. The bike chassis went back to LA and the engine remained for repairs.

I searched around for a set of cylinders that could be cleaned up and re-bored, but little was available. The owner finally tore down a spare “rebuilt” engine to extract the cylinder and pistons. The pistons were .50 and the cylinders were fairly well-honed, so I just bolted up the parts to the bottom case, installed the cylinder head and camchain, and reassembled it all again.

We reinstalled the engine into the chassis and refitted all the bits until it looked like a whole bike again. It started up after a few kicks but wasn’t idling well, so it was back to pulling pilot jets again and cleaning them out, checking float levels, and dialing in the ignition timing. The bike went out for a test run and seemed to be running well, but loudly due to straight pipes. The bike went back to LA seemingly running well and was taken out for some local rides successfully. The owner decided to sell the bike and wound up shipping it to a mutual friend on the East Coast. Soon after the bike arrived at its new home, the new owner took it out for a test run and about 15 minutes into the drive.. BANG!

It did it again! Same side of the engine, the same type of damage… broken sleeve flange and broken piston/rings.

Collective thoughts were shared online within some private conversations, but the consensus was that the sleeves were loose in the cylinder casting, reducing the amount of heat transfer from the piston to the sleeve to the cylinder block fins for heat dissipation. With piston clearances in the one to two thousandths range, it doesn’t take much to cause them to seize, but breaking the same right side sleeve and piston on the same engine, in the same manner, is more than just a little mystery. Bang, BANG!

Lastly, my friend of many years owns a 1962 Falcon Ranchero and has driven it almost daily for over 20 years. The truck as suffered all kinds of mechanical maladies and some accident damage here and there but was pretty much reliable for short trips to the store and work. A few weeks ago, she got into the truck, turned on the ignition, started the engine, pushed in the clutch pedal to engage 1st gear of the 3-speed manual transmission, and suddenly it all went BANG! The starter was no longer able to turn the engine over and a quick check revealed that the crankshaft was seized up solid for reasons not readily known.

It was towed to my house as I felt that probably the timing chain had broken and wrapped around the crankshaft upfront. After an hour of removing the cooling system and timing chain cover, the results were unremarkable. The timing chain was loose, but still connected to the sprockets and the engine still refused to budge an inch.

We had the truck towed back to her house and rolled into the 1 car garage, which was filled with plastic storage boxes along the whole rear wall, with a toolbox and other assorted packages and furniture bits pushed to the sides. With about 18” of room on both sides, I managed to get the truck up on a couple of jack stands and remove the oil pan to check the crankshaft for a thrown rod or seized bearing… nothing.

Figuring that the engine would probably have to come out anyway, I removed the driveshaft, then the transmission, and finally the bell housing. When the bell housing was backed off of the engine block there was a “clink” noise and a piece of the pressure plate pivot dropped to the floor. For reasons unknown, the piece broke off of the pressure plate when she had pushed in the clutch pedal and the running engine spun the piece up in between the pressure place and inside of the bell housing, jamming the crankshaft.

The clutch plate was almost down to the rivets anyway, so the whole clutch was replaced along with the throw-out bearing. I was unable to extract the pilot bearing which was a small ball bearing instead of a brass bushing, so it was left as-is. Using a bike lift stand slid under the truck, I was able to reinstall the transmission after a great deal of effort and force. The oil pan was reinstalled with a new gasket, as was the front cover after a new timing chain and gears were put in place.

Once the engine was restarted, it became evident that the six-cylinder engine was only running on five cylinders. The number three cylinder wasn’t firing, but the big mystery to that was the spark plug and wire were fine, but no spark was coming out of the distributor cap just on number three! Changing the cap didn’t fix it and finally, I realized that the distributor shaft was worn out so far as to change the point gap at least. .020”

Somehow, when running the wobbling shaft was skipping number three cylinder! A rebuilt distributor solved the problem and the truck began running on all six cylinders once again. While success was achieved in getting the engine to run again, a leaking pinion shaft seal at the rear axle has drained out a good bit of the gear oil and is causing gear noise at the rear axle. That repair will have to go to a shop as I have become fully depleted by the work entailed in bringing a 50-year-old Ford Falcon Ranchero back to a half-life state.

PS. On the way to the transmission shop, the truck died quietly on the freeway about a mile from home. It was towed to the shop where the mechanic said that the pinion bearing was worn and a new seal wasn’t going to fix the leak problem. AAA came and got the truck, brought it to my house where I diagnosed that the new points in the rebuilt distributor had worn themselves down to nothing in less than 20 miles. I cranked the points back open to .025” again, the truck fired up and drove home without issues. The crappy points were replaced with Blue Streak brand units and the truck continues to run the best that it can.  However, the writing was on the wall about the long-term reliability of this 60-year-old Falcon, so it was replaced by a 2003 Mini-Cooper! So, I bid farewell to the Ranchero (aka Mr. Toad) and its mechanical neediness.

Hopefully, that is the end of the big bang adventures.

Bill Silver

aka MrHonda