Leaking sump replaced, complete oil and oil filter replacement, carburetors replaced with newer rebuilt versions

Current odometer reading: 48700 miles

Oil sump pan had been leaking profusely, due to the previous practice of using the oil level sensor hole as a means to drain the hole having cracked the said oil level sensor. It was therefore decided to replace it with an intact one, including a new oil level sensor. A replacement oil pan and sensor was procured, and was installed with a new Athena gasket and blue Hylomar. In addition, a new oil level drain bolt and new Wemoto oil drain washer was fitted. A new Demon Tweeks oil filter was installed, and the oil replaced with new oil: Shell Advance 15W40 mineral motorcycle oil.

Exhaust leak type of noise was noted while riding the bike. It was considered that the cause was worn out exhaust gaskets, so new ones were procured and installed. However, this was not the problem. The problem was traced to a vacuum leak from the carburetor 3. The vacuum leak had a serious cause: the top of the carb had come off, and the spring and main needle had flown out from it. As replacement carb parts for these original Mikuni BDST28 x 4 were unavailable (a new plastic carb top, new diaphragm spring and needle would have been needed) it was decided to obtain a complete set of replacement carbs. The only ones available were a set of Mikuni BDS28 x 4 (from a 1999 model). These were different carbs, but intended for this model of bike. These carbs do not have an oil-fed carb heating system. The carbs were in a neglected state, and required a full stripdown, including separation. They were thoroughly cleaned, the float levels were set, the mixture screws were set, and they were balanced. The oil feed to and from the carbs (on the bike) were then capped off, and these new carbs were installed and tested. Idle speed set to 1200rpm – dead steady. Working perfectly.

Starter (intermittent) issue was observed: occasionally a single click, followed by nothing, would result from an attempt to start the bike. All connections tested and found to be working correctly. Battery had more than sufficient power. Solenoid and starter relay tested, and found to be working. Problem identified as the starter motor. This was stripped down and the commutator was cleaned. This completely solved the problem. However, it was noted that one of the brushes is significantly worn. The starter motor shall be rebuilt in due course.

Bike fully reassembled and working correctly.


Fork springs shimmed to increase stiffness

Current odometer reading: 48416 miles.

Following the steel braided cable installation, which makes the braking work much more quickly and with less lever travel, the bike tends to dive excessively when the front brake is applied. It was therefore to decided to increase the standard fork springs’ stiffness slightly.

Shims were fabricated from 3-4mm steel wire, and placed between the fork springs and the washer that goes beneath the standard fork collet/tube, at the top of the forks.

Braided steel front brake cable fitted

The existing front brake cable was rubber-coated PTFE, and was showing signs of wear, and was suspected of not fully exploiting the braking power of the recently changed brake pads and brake fluid and reconditioned caliper. It was probably the original brake cable (25 years old). It was therefore decided to replace it with a new braided steel cable. The copper crush washers around the banjo bolts on the old brake cable were reused after being re-annealed by heating until red-hot. Tested and working, with greatly improved braking performance.

New (4-degree advanced) ignition timing plate fitted

Current odometer reading: 48072 miles.

In keeping with normal practice with the XJ600S, which has a slightly retarded ignition timing in order to retain compatibility with low octane fuels, a corrected (4-degree advanced) ignition timing plate was procured and fitted, and the old one put into storage. This was in order to make the engine run as per standard specifications as set by the manufacturer.

Inlet-side valve over cylinder 4 shimmed

Current odometer reading: 47717 miles.

A new 275 valve shim was procured by mail order.

The new valve shim was inserted above the cylinder 4 inlet-side valve, and the old 280 valve shim was put into storage.

Updated (current) valve clearances are as follows:

Inlet 1:         0.15

Exhaust 1:  0.24

Inlet 2:         0.12

Exhaust 2:  0.22

Inlet 3:         0.12

Exhaust 3:  0.22

Inlet 4:         0.15

Exhaust 4:  0.25


Oil drained and changed; new sump plug fitted

Current odometer reading: 47479 miles.

All oil replaced. Shell Advance 15W-40, mineral motorcycle oil.

Oil was last replaced at 45221 miles. Therefore this is an oil change after an interval of only 2258 miles. Haynes recommends an oil change every 4000 miles, and an oil filter change every other oil change (i.e. every 8000 miles). However, it was decided to replace the oil much earlier than 4000 miles, as the oil I had been running was a mineral oil (just like its replacement) and mineral oils are less resilient. However, the drained oil still appeared very viscous, and it is considered that it would be safe to relax this oil change regimen and replace it every 3000 miles instead, which still exceeds Haynes recommendations.

In addition, a new sump plug (universal 14mm diameter, 1.5mm thread type) was fitted. This was advertised as a “Rimlex sealing plug” that doesn’t require a copper crush washer, yet is reuseable.

Oil pump drive pin fabricated and replaced; stuck oil sump plug removed

It was decided to remedy the clutch rattle for which this model of bike is notorious. The cause of the clutch rattle in this model of bike is widely known to be an improperly sized oil drive gear dowel. This is a small steel dowel that attaches the oil drive gear to the back of the clutch basket.

The clutch basket was removed and the oil pump drive pin/dowel was removed. It was noted that there was significant play caused by this pin/dowel being too small. Its actual dimensions are 4.5mm diameter, 10mm length. The diameter was too small, by almost half of a millimetre. This would have been the cause of the bike making an unpleasant rattle below 2000 rpm. A section of steel wire (from an Allen key) was procured, and cut and filed to size. This was then installed, and the clutch reassembled.

The stuck sump plug bolt, previously the cause of having to drain the oil by means of the oil level sensor and a hand pump rather than the proper way, was removed with the help of a local welder.

The bike and the clutch rattle fix shall be tested when a new sump plug bolt has arrived through the post.

Valve clearances checked again, and exhaust repair carried out

Current odometer reading: 47298 miles.

It was noted that a visible crack had appeared between the chrome silencer section of the exhaust and the chrome-plated thin steel part that followed the joining pipe. However, no exhaust gases were blowing from this crack. It was surmised that the crack was probably filled with nothing more than corrosion, that the exhaust was structurally sound but that a large hole would appear if the crack were not addressed.

It was therefore decided to repair the crack with Milliput, as a permanent repair. Previous experience with this product led to the decision to make a continuous Milliput band around the pipe, that was larger than the crack itself, to prevent the repair breaking loose. This was then painted in matt black paint.

It was also decided to check the valve clearances again, as it had been over 2000 miles since the valves had all been shimmed. The following readings were obtained:

Inlet 1:          0.15-0.16

Exhaust 1:   0.24

Inlet 2:          0.12

Exhaust 2:   0.22-0.23

Inlet 3:          0.12

Exhaust 3:   0.22

Inlet 4:          0.1-0.11

Exhaust 4:   0.25

All of the clearances are satisfactory, and the bike shall continue to be used normally. It was noted that the shim on inlet 4 would need replacement, probably within the next 4000 miles. A 275 shim has been ordered, and will be inserted at the next oil and oil filter replacement.