Shannons Dream Bike Build Episode 2: Engine Problems
In this next episode of the Shannons Dream Bike Build we start working through the engine build for this Honda CB500…or Cb550?
As we dive into our first steps of the revival of Scotts CB500 we have a few surprises on the way. Nothing we can’t handle though, and definitely nothing we haven’t seen before. First steps are making sure we have the powerplant sorted out as the base of our café racer build.
The engine as we received it was not running, and hadn’t been for years. We pull the engine out, and run through a few tests on the top end before tearing down. This gives us a little insight into the condition of the top end, and can reveal clues about just what we’re getting ourselves into. With the compression and leakdown tests complete we have our engine builder Jesse begin the rebuild process.
The test revealed a tired engine with low compression, but not to the point that it wouldn’t run. We had a leaky valve or 2, but the bike moved freely. Now we get into the hands on inspection of this 50 year old motor. The top end or head revealed exactly what we expected, an engine with reasonable wear and tear, valve springs just out of tolerance but no major damage. The bottom end is where things got a little interesting. With the tear down complete and the engine laid out on our work bench, we started measuring tolerances and running over the components with a sharp eye.
Right away Jesse noticed an issue on the crank and bearing retainers in the case. The engine showed signs of being run hot, or with low oil at some stage which had caused one of the white metal bearings to let go and spin in the case. This causes accelerated wear on both the crank and case. Not ideal, but you come to expect these little surprises when dealing with vintage engines as often as we do.
There are a few ways to approach an issue like this. We can have the case and crank repaired and re-machined to accept oversize bearings, replace the crank and case with known good parts, or just swap engines with one in better condition. The first option is usually the most expensive and the other 2 are about the same usually. But usually your bike build doesn’t have a filming deadline to meet, and usually your bike builder won’t have a spare Honda CB550 engine sitting in his garage.
To keep this project on track and on time I decided to swap out Scott’s CB500 engine with a spare CB550 engine I had acquired in my wheeling and dealing. I put in a call with Scott about our findings and he was on board for the free 50cc’s we were about to give him. So the build progressed with my spare donor motor.
Our process was quickly repeated and parts order placed for the CB550 engine rebuild. All new top end was a given with high compression pistons, new valve train and re-machined head matched up to ported and polished intake and exhaust ports. We also replaced all bearings and seals on the bottom end along with the conrods and associated fasteners, clutch and tested the stator to ensure it would operate as required.
As the parts crept towards us from all corners of the globe, we got busy with the machining work, port and polish, sent the vapour blasting out to be done and got our external covers polished with a few parts chromed for good measure. We also placed a few calls to get the new Mikuni RS carbs, DNA filters, and Dynatek ignition on the way.
During our downtime here Dylan and I got busy setting up for the next stage of the build – fabrication. With all things building from a solid foundation is essential. The fresh engine was the first part of that, the wheels and suspension were the next. CB500’s as standard run a 19” front 18” rear. In the interest of sharper handling, a better stance and a nicer over all look we messed with this formula a little. The hubs were stripped, polished and re-laced to a set of H-pattern or valanced rims 18” x 2.5 up front and 18” x 3.5 in the rear.
This mod lowers the front end slightly, gives a quicker corner feel and gives you wider tyres front and back, there is quite plainly no downside. Along with our upgraded wheel and tyre set, we wanted to upgrade the braking.
Anyone who’s ridden an old bike knows that when you’re barrelling into a corner you squeeze that lever and there’s some braking for sure, but mostly you’re relying on hopes and dreams to pull you up. We’ve done away with the 1970’s calliper and replaced it with a mid 2000’s twin pot Nissin unit re-purposed off an SV650. Mounted on a custom fabricated bracket that still utilises the standard brake rotor and spacing of the original Honda CB550 four.
Our last job before the engine went back in was to strip the tired old forks and rebuild them with fresh chrome fork legs, updated internals and mount it back up with a custom top triple clamp.
As Jesse was finishing up the engine work and assembly, the rolling chassis was put together with the fresh parts and the brand new CB550 four motor bolted back in. The stage was set for the next leg of our journey with the Shannons dream bike build – Fabrication.
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