Minutiae; It is all in the details…

Recently, I had a call about a local CL72 owner who was seeking help for his 1965 model Scrambler, which was having numerous performance problems. He was located in N. San Diego County, so I referred him to my friend Randy Troy, who lived just a few blocks away. Randy has had years of experience in working on all kinds of Hondas and was trained as a Porsche mechanic and worked at a Datsun dealer back in the 1970s. He has a deep understanding about the “how’s and whys” of how things work, but had never been hands-on with a 250-305 Honda twin before.

He began with a basic tune-up to get it up and running, but encountered problems right away. The carburetors would fuel foul the spark plugs quite quickly, so the first thing he did was to remove the carburetors for inspection and cleaning/adjusting. If you have worked on any Honda Scrambler, you know what a PIA it is to get to that left side carburetor for any kind of service or removal. In the past few weeks, he’s become proficient in doing that job!

With the air filter tubes off, he was watching fuel spitting back into the inlets, even at idle, which is never a good sign. The compression readings were about 130 psi, which is about 20 psi low. This generally indicates that the cam timing is slightly retarded (a half tooth, which is remedied by changing a tooth on the crankshaft, not the camshaft). Sure enough the cam timing was off. Fortunately, only a CL72-77 allows for the top engine cover to be removed with the engine in the chassis, which allows for cam timing verification and adjustment. 

With the top cover off and spark plugs removed, the first thing to do is to anchor the head/cylinder to the engine cases, by putting some short  sockets on the studs secured with some nuts. This keeps the top end from lifting when you turn the engine over. First you have to locate the master link on the camchain, then carefully disassemble it and string some wire through the ends. Loosening the valve adjusters takes the camshaft lobe load off the cam, so it can be positioned in a way that the flats on the camsprocket are level with the top of the cylinder head.

Once the cam position is set, you have to jiggle the crankshaft around with the camchain ends held in such a way as to allow the crankshaft to bring the right piston up to TDC AND the ends of the camchain towards the top to reattach the master link once the timing is set. There is a lot of fiddling around to get this all to happen, but Randy did achieve the goal and the cam timing was back to where it belonged. 

Once that was done, then the carbs got a long look. Randy noticed that there was wear and corrosion on the needle jets that might have caused some fuel spray problems. He was lucky to find a new set of needle jets at David Silver Spares, which arrived in a few days. Then he mentioned the other calibrations of the jets, which were not quite correct. He found #120 main jets and #40 idle jets in place of the normal #115 mains and #38 idle jets. On top of that he read out the needle codes, which turned out to belong to a CB72, not a CL72. The CB72s have a “power jet” fuel enrichening system which calls for a different needle taper. Stock OEM CL72 needles are NLA now so Randy had to order the oft-maligned Keyster carb repair kits, which come with new needles, float valve, gaskets, etc.

Keyster kits are made in Japan, but have been found to have incorrect metering needle tapers and poorly fitting float bowl gaskets in the past. When the kits came in the gasket issues apparently remained and the needles were of a different taper than the CB72 needles, so that might be a solution for the rich running. With new needle jets and Keyster needles, the bike ran too lean off the bottom end, but the fuel backflow problems at idle were solved. The needle clips were lowered to the bottom notches in order to richen up the transition from idle through mid-range, which improved fueling somewhat.

Randy also learned about the ignition timing vagaries associated with having the camsprocket controlling the spark advance curve. He set the initial ignition timing statically with a 12v test light, but discovered that running ignition timing often does not reflect the initial settings. In order to prevent over-advancing the spark timing, the idle timing had to be retarded back towards the T mark instead of the F (firing) mark. 

Changing the ignition timing alters the vacuum signal to the carburetor metering systems, which causes the mechanic to have to alter carburetor mixture and idle speed settings. The ignition timing and carburetor settings are inextricably intertwined and there is not that much you can do about the ignition timing without tearing the cam shaft sprocket out for repairs or replacement. There is inherent slop and inaccuracies with this camshaft driven ignition system that cannot be completely overcome with a used engine.

With new carb parts, many of the performance issues began to subside, but Randy feels like the bike is still a little bit flat in the mid-range, so he bumped the main jets up to #125 to see how it worked; especially when jetting for today’s alcohol-blended fuels.

After all this intensive work to exorcise the demons of this bike, his test rides have highlighted a 2^nd gear jumping out issue, which requires an engine removal and cases split to remedy the transmission woes.  Carb jetting is still a bit off, mostly due to a lack of available OEM jet needles for a CL72. Sometimes you just do the best you can with what you have and then give it back to the customer highlighting the known remaining issues and an estimated cost to fix them properly. Randy probably got paid about half of what the job was really worth, time-wise, but he was appreciative of the chance to learn all about the mysteries of the 250-305 Honda twins.

To paraphrase Forrest Gump’s comments: “Vintage Hondas are like a box of chocolates; you just don’t know what you are going to get.”

Orphan Exchange; a twin for a single

Those who know me well are aware of my fondness for the Kawasaki W650 models, which were only sent to the US market for two years (2000-2001). I have owned three of them over the past 9 years, with two 2000 models and the last one a desirable 2001. The 2001s had some subtle changes to the front axle, steering head angle, rear fender and were painted a lovely two-tone Dark Green over a Cream bottom portion.

Due to a plethora of bikes that have been coming and going in the past year, I decided to let the 2001 bike go and advertised it on the local Craigslist as well as once on eBay, but with no results. The bike only had 9k miles on it, was all dialed in with carb jetting and suspension upgrades and was driven briskly on Sunday mornings with my friends the Jamul-igans. With skinny tires and forks, plus about ½ of the other’s horsepower ratings, the bike was driven hard, but not abused. Previous crash damage was mostly all repaired; leaving only a few spots of scrapes and paint chips. It put a smile on my face every time I drove it, but it was a bit too big and ungainly for quick trips to the local Post Office or auto parts stores. Historically, I don’t keep vehicles much longer than a year or two, so the time was up for this fine machine.

Most of the Craigslist responses were scammers trying to get my email address or phone number for nefarious purposes, but one reply came from a man in Rocklin, CA (550 miles from Spring Valley) who was “ready to buy” and even considered flying down and riding it back home. The only holdup on his plan was that he was trying to sell his 1990 GB500 TT bike, which was somewhat weathered and had 29k miles showing on the speedometer. The sales efforts were non-starters for various reasons, so after we exchanged messages back and forth for a couple of weeks, I decided that I would offer a swap; his GB500 for my W650. He agreed to meet me “half way” between SV and Rocklin at Visalia, CA, where my cousin has lived for over 40 years.

The photos of the GB500 were less than detailed, but I figured that a licensed, running GB500 with mostly all original parts was equal in value to what I was trying to get for the W650. So, one Friday morning, at 4AM, I launched my Toyota Tacoma up the I-5 with the Kawasaki W650 secured in the bed. The plan was to get through LA traffic before it became unbearable during rush (?) hour. I had agreed to meet up in Visalia at noon time, to give us both plenty of time to arrive at the destination. Well, my plan was a little too optimistic, perhaps, as I arrived some 300 miles from home at 9:30AM!

Texts from the GB500 man indicated that he didn’t leave Rocklin until 6:30AM, which took him right into downtown Sacramento traffic at 7AM, so he was delayed quite a bit on his end of the journey. 

In the meantime, I spent time with my cousin who owns a thriving auto repair shop in Visalia and is a real “gearhead” kind of guy, owning a couple of 1960s Mopar drag cars equipped with Hemi engines, as well as an airplane and some pricey automobiles and trucks. It was great to catch up with him during my 3 hour stay, but I finally decided to leave the shop for the rendezvous near the Highway 99 Junction which was about 8 miles away. While I was driving, he sent a text indicating that he had taken the wrong off-ramp and was turning around to the intended location. As I came upon that same off-ramp, I looked ahead to see his car (Honda Element) just getting back on the freeway. I went back on the freeway ramp and followed him right to the Chevron station that we had agreed upon as the meeting place. Good timing!

Yes, the GB500 came down in the back of a Honda Element SUV, actually fitting in quite nicely. We unloaded our bikes, took a quick test ride to confirm that this is what we really wanted to do, then swapped bikes into each other’s vehicles, completed paperwork and headed off for home, once again.

I was a little disappointed with the overall condition of the GB500, as the alloy parts were mostly corroded, however most of the chrome plating was relatively clean. Apparently the bike lived in Oakland for awhile, near the bay and was obviously ridden a great deal in the past 27 years, so wear and tear is expected to a certain extent. My biggest concern was the noises coming from the engine, as it was fired up cold. It was hard to pin down the specific area of the engine where the noises were occurring, but it was a bit unnerving to say the least. The bike ran fine on the test run, so I just decided to go forward with the deal and fix whatever was necessary later on.

I ran back down the 99 to the I-5 junction, then up over the Grapevine pass to the 210 highway junction, which I took to my friend Myke’s place in Sunland, CA. The total mileage covered for the day was about 500, all in 13 hours. I enjoyed some rest and a nice Thai meal nearby and went to bed planning on an early start on Sat morning, in order to miss the always busy southbound freeway traffic headed into San Diego.

I launched at 6:30AM and headed way east towards the I-15 southbound, where traffic was racing along at 70-85mph, making the return leg of 180 miles in 3 hours. I unloaded the bike, unpacked and then stripped the tank off of the bike to see what was underneath the bodywork and perhaps pin down the source of the engine rattle. With the help of S100 cleaner and a hose, I was able to clean the bike up pretty well, followed by a blow-dry session with the air compressor.

I checked the valve clearances, which were just slightly loose and attended to an odd oil leak that was coming out of the center of the rocker arm cover. The bolts for the cover are all supposed to be dry, so I was able to squeeze a little 8mm o-ring over the bolt head (it was too long to remove with the engine in place) and then retorqued the bolt, hoping for an effective repair of that problem. I finished up by installing a fresh spark plug and removing the rest of the pollution control devices and hoses which were partially taken off by the previous owner.

Both tires were under 20psi, so I aired them up, checked the oil level and the chain tension and headed out for a test ride around the neighborhood. The bike ran well and was responsive to the throttle, but the clamor coming from the engine continued to puzzle me. I decided to take the GB500 on the Sunday ride and see if it would break something or if the noises were just excessive piston slap on a 92mm wide piston, churning up and down with a redline of 8k rpms.

Well, the Sunday ride went well and I thrashed it as much as was reasonable under the circumstances. Unfortunately a prior owner installed oversized tires on both ends, so a good deal of caution was taken not to get them way out on their sidewalls. The tires are Bridgestone BT45s, which are grippy things, but these were getting sidewall cracks due to age.

Back home, after the ride, I did research on the GB500 noise problem and found a detailed webpage that described having to replace the piston at 27k miles on his machine, plus he rebuilt the crankshaft with a rod kit which is available. The engines are related to the early XL/XR500-600s, so some of the parts will interchange. Supposedly, the 97mm XL600 piston and cylinder will mount up on the GB500 cases, giving a 100cc displacement increase. Other models use a 100mm piston, but that is probably really pushing it, unless you do a full-on rebuild.

Top end teardown

After the successful Sunday ride, I decided to drain the oil and pull off the top end to see what might be causing some of the noises inside the engine. Fortunately, the top end can be removed with the engine still in the chassis. You can pull the head off and away from the carburetor/manifold/air box with those components all safely in place.

The top cover has the rocker arms all installed and the first bit of bad news was that both of the exhaust rocker arm pads were worn down excessively. The good news is that the intake sides were all just fine. The center of the cam runs directly on the cylinder head bearing, which is oiled by an oil feed hole in the camshaft. The cylinder head side was scored and roughed up like the exhaust rockers, but the top cover bearing surface was like new.

After figuring out how to extract the camshaft from the sprocket and two ball bearings, the head was ready to remove. There didn’t seem to be a lot of deposits or moist carbon on the valve heads or the piston crown, as if someone had been in there before, freshening up the internals. Sure enough, despite a lack of markings on the piston, the piston rings had .25 marked on the edges. The piston didn’t show any signs of distress or a great deal of wear. The cylinder bore still had nice cross-hatch marks on most of the surfaces, but when the rings were removed from the piston and stuck back into the bore, the end gap was .025” to .035” on the two top rings. Normal specs are about .012” to .016” using the standard reference of .0045 inches of end gap per each one inch of cylinder bore. I had my machinist friend measure the piston and bore size accurately and he determined that the piston clearance was about .003” which is near the wear limit of .004” that Honda recommends. He felt that the piston clearances were not sufficient to create the kind of engine noises that I was hearing.

With the 24mm piston pin removed from the piston and refitted to the rod end, it was evident that there was enough clearance to give a loose rocking fit to the pin in the rod end. Most likely, this is the main source of the engine noise. The remedy is to install a $125 rod kit in the crankshaft, once the engine is pulled all the way apart and a machinist presses the crank apart and back together again with the new rod kit. Not what I had in mind for this little bike project.

All apart…        

The bottom end was pulled out of the chassis and put on the bench for disassembly in order to replace the connecting rod in the crankshaft. There are several locking nuts inside to secure the clutch hub and other critical components, which needed a 24mm socket and air wrench to remove. Once the locking nuts were removed, the rest of the engine more or less melts apart into transmission and counter-balancer units along with the huge ball bearing which supports the crankshaft in one case half.

While waiting for the arrival of the connecting rod kit, cleaning and some painting was done to the top end components, along with replacing the valve stem seals in the head. The valves were de-carboned and the combustion chamber cleaned up of old burned oil residues. The inside of the engine was quite clean, so regular oil changes must have been done in the past 27 years. New gaskets and seals were procured via the Internet, but it was surprising how few parts are left available for these bikes now.  A SoCal dealer had a new set of .25 oversized rings, which when checked in the cylinder bore did show a reduction in the end gap measurements over the old ones removed.

A local camshaft manufacturing shop felt they could regrind the lobes without having to dig too deep into the base circle (schneidercams.com) so they took the old camshaft in for a couple of week wait in their queue. New OEM rocker arms were purchased through the local Honda dealer, so the major pieces are coming together finally.

Because of the miles on the bike, a decision was made to buy an aftermarket starter motor repair kit and freshen up the starter motor before it was returned to the engine cases. Once apart, there was very little wear showing on the brushes, so the kit was left unopened and will go with the bike to the next owner someday in the future.

The carburetor still hung in the airbox, so it was an easy task to remove the throttle cables and enrichener, loosen the clamp and remove the whole carb as a unit for cleaning and inspection. In all likelihood the carburetor had never been serviced as it was still jetted to the CA spec 142 main jet size. I didn’t have any 145-ish jets handy, so used my tapered jet reamers to open it up more towards a 148-150 size. With a fresh motor, use of alcohol-based gasoline and the possibility of a slightly modified camshaft grind, a little more fuel is generally a good step towards improved performance.

The crankshaft was taken to a local machinist friend, who found difficulties in attempting to remove the crankpin from the assembly due to a close-fitting sprocket pushed up against the crankshaft cheek. Finally, he just pressed the easy side off and checked the pin for wear and damage. The pin checked out fine, so the new rod was installed and the crankshaft pressed back together again. Finally, he had to gently press the crankshaft back into the engine case half to complete the job.

With the crankshaft done, assembly work could resume and all the little bits and pieces reinstalled where they belonged. 

I had the unfortunate experience of buying an “Engine bolt kit” from an eBay seller which appeared to be a complete kit, but was found to be missing the crankcase bolts. Emailing back to him was frustrating as I was told that if I had “read” the details I would have seen that the crankcase bolts were not a part of the “kit” and were available at an extra, undefined charge. This was all buried in a dozen paragraphs once you hit the “SEE DETAILS” section. Why he chose to offer a “kit” without the critical center case bolts is a mystery and he never would say why he did it or why he didn’t list the price of the extra bolts in his auction. After some unpleasant exchanges, I paid an additional $25 for a handful of bolts, which the seller then cancelled and decided to block me from future business, leaving me without the final matching bolts to finish putting the engine back together with.

Another seller on eBay did offer the center case bolts as part of their main kit, but I only needed the few not a whole kit. His main website offered individual bolts and fasteners in an easy to use menu, so I ordered up what I needed from there and awaited delivery. It was a very frustrating experience to say the least and has held me up an extra week, just because the seller decided to play games with his product offerings.

In the meantime, the front brakes were addressed with a caliper rebuild, new pads and a fresh master cylinder kit installation. New BT45 tires were spooned onto the rims and fresh rear wheel dampers installed in the rear hub.

Drama and Difficulties

After several weeks, the cam grinding company discovered that they couldn’t grind the cam lobe next to the de-compressor parts attached, so took it to a nearby machine shop which took 2 tries to get the end pieces pressed off. Apparently they only had an arbor press not a hydraulic one. They finally get it loose, with the bits flying all over the floor. They claimed to have found them all but later on I discovered that the thrust washer was not in the bag of bits. With the de-compressor parts removed, they were able to grind the cam and Parkerize it afterwards. When I took it back to my local machinist friend’s shop we discovered the missing thrust washer. I ordered a new one from Honda, but the only ones were in warehouses back East and it took a week to get one out to SoCal. In the meantime I found that the oil filter washer from a CB750 was about the right size, so I used that when the parts were pressed back onto the end of the camshaft.

I thought I was near completion when I discovered that the funky cylinder head-mounted camchain tensioner requires a Honda special tool in order to retract the tension from the camchain guides. The tools are available for about $50, so I ordered one of those, too. In the meantime I tried to wrestle the engine back into the chassis by myself and fought it for more than an hour before it finally found just the right positioning to get the mounting bolts installed. The only other GB500 engine install I have done was when I lived in Hawaii and that time I wound up laying the engine on the floor and dropping the frame over the engine so I could get the alignment done. It is a total PIA and the frame tubes are all scratched up from the wrestling match efforts.  Apart from flywheel pullers, I have never had to use a special tool to reassemble a Honda engine until this one. Nevermore!

On the home stretch…

From the time the bike was picked up, it has been almost exactly 2 months of work and waiting to get the GB500 back up and running again. After several weeks of waiting the camshaft was ground, but the result was that the de-compressor gear really didn’t want to work with the re-profiled cam lobes, so the whole assembly was removed from the camshaft. Apparently only the US versions of these bikes had one in the first place, so no big deal to remove the de-compressor parts.

Just as I thought the end was in sight, the first firing of the engine revealed a pair of exhaust leaks. I had ordered the wrong head gasket (XR500, instead of the one for the GB500) and it didn’t have the extended sections to encompass the PAIR (pulse air) system transfer ports! It took another three hours to R&R the cylinder head gasket to repair the exhaust leak problem. Once that was finally accomplished, the bike fired up once again and seemed to be running well.

Several local road tests failed to reveal any major further issues, so the bike was taken out on our Sunday morning rides up into the mountains and back, about a 65 mile round trip. With scuffed in new BT45 tires, new front brake system overhaul and new pads, everything is getting a new break-in period, but so far it seems to have been a success in the end… but what a lot of work and expense!