Having gone through the three times engine pull/repair on an early 1965 CL77 305 Scrambler, I now have a follow-up 1964 CL72 250 Scrambler in the shop for similar repairs. In both cases, the bikes were physically restored with new paint, polish, chrome and exterior restoration work, but the engines were unknowns until they got to me.
This shiny red CL72 was brought down from its Utah home to “get it running properly” after all the restoration work was completed. The bike started out as a “basket case” with its current owner, who is an accomplished auto restoration expert, but had never rebuilt a bike before. He did, however, own a 250 Scrambler when he was in his youth and wanted to relive that experience once again.
In some respects, having to extract a motor from a restored chassis is especially nerve-wracking because you want to minimize the scratching damage that goes with wrestling a 100 lb motor out and back into a freshly painted frame. I pad the frame rails with rags and tape, as much as possible, to help reduce contact damage, but you know that something will shift or go wrong and it always leaves a mark somewhere.
The owner had really gotten the bike to a run-ready state, but didn’t known the fine details of tuning and engine setup. He had it running ever so briefly and said that it wouldn’t idle, didn’t seem to be charging and one side of the exhaust was smoking to a certain extent.
It arrived with a dead battery, so that went on the charger first, then the seat and fuel tank were removed to access valve covers for a valve clearance check and also to remove the carburetor set, which also requires removal of the exhaust pipes, left side cover and air filter/tube. The left carb just does squeak past the oil dipstick tube, as you lift it off of the two intake manifold studs. As soon as the carb set was removed a BIG issue became immediately apparent. There were two different carbs mounted on the bike! The left side was a CL72 carb and the right one was a “power jet” CB72 unit. They have two different jetting calibrations, due to the way they deliver the fuel curve, but this set of carbs had #100 main jets in both carbs, plus an unknown aftermarket needle in the left carb and the CB72 needle in the right side. Two left side carb tops were installed, as well. Dropping the fuel bowls revealed some very stale gasoline left behind, along with one stuck float valve needle and 24mm float level settings which should have been 26.5mm.
A quick compression check, after valve adjustment, showed 120 psi in one side and 140 in the other cylinder. These early 1964 engines came with 9.5:1 compression pistons (lowered to 8.5:1 in 1965), so the compression readings should have been up in the 160-175psi range. I relayed the information to the owner who directed me to pull the motor and get it right, in order to match the rest of the work/condition of the bike. So, out it came in about 30 minutes.
As soon as I pulled the kickstarter cover, I saw a little dribble of oil in the bottom of the engine case, but no signs of oil leaks at the crankshaft seal. Uh, oh! I looked above the rotor, once the stator was removed and sure enough another chunk of engine case was missing due to the mis-installation of the crankshaft bearings on their locating pins. This must be the fourth or fifth one of these “mistakes” I hae had to repair in the past couple of years. Seeing that assured me that someone else had been inside the motor before and then all bets are off as to what will be found during teardown.
Here’s what I found: (Excerpt from my diagnosis page written to the owner)
R&R carburetors for cleaning. One carb is a CB72 unit, not CL72. Located and purchased good used CL72 carb body for rebuilding. Ordered new needles, jet holders, carb top
Found broken engine case where the crankcase locating pin was pushed through, due to previous repair attempts in the past.
Found piston ring gaps at about .080” instead of .008. Pistons are .75 o/s. Cylinder bores are scored.
Found loose camsprocket rivets, loose advancer weight spring on one side.
Determined that previous repairs did include replacement of low gear bushing and offset cotters.
Found primary chain stretched out enough to wear into the clutch cover.
Found 6-plate clutch plate assembly stuck in place. Steel plates rusted and retainer springs were missing from clutch pack on inner hub.
Found oil filter seized on filter shaft and the whole thing spinning inside the cases/outer cover. Locating pin sheared off.
Camchain worn out. Camchain tensioner roller badly deformed/worn.
Valves/seats worn into a wide contact pattern, but valve stem tips not dished out.
Camshaft lobes have some light pitting, but are serviceable. Camshaft rocker arm surfaces okay.
Crankshaft roller bearing surface pitted/rusted, damaging rollers. Rods had excessive side play/rock.
I used paint stripper on painted engine parts, then took it to a car wash for blasting/cleaning. Will require further cleaning to assure no contamination of engine parts. (Owner had rattle-canned the engine with silver paint which was not durable or fuel resistant.)
So, there you have it, just another typical Honda 250-305 overhaul project, once again! Fortunately, I had a spare CL77 crankshaft (different balance factor, but not a critical issue) to use with good bearing surfaces and nice tight connecting rods. I am running down to the last of my NLA hard to find engine parts now, though. Primary chains, camchain tensioners, camshaft sprockets, etc. are all very hard to find now and expensive when you do. This may be one of the last engines that I overhaul because of a lack of parts availability. Stay tuned for more chapters of this Scrambler story!
BTW. The customer wanted an electronic ignition system installed, so that was added to his parts bill, which is in excess of $1,100 so far. You really can't do these engines and bikes on the cheap anymore.
Bill “MrHonda” Silver