Honda CBX1000 engine rebuild

A Honda CBX1000 engine rebuild is not something that should be taken on by a home mechanic in their shed or garage. In 1978 most of the top mechanics for Honda were either flown to Japan or sent to Honda Britain to be trained in the CBX specifically. These motors are unique, quite complex and there is a lot of knowledge required about how these engines work and are put together before touching them. The time has come to rebuild these motors now because the cam chain tensioners are at the end of their life.  They are made of nylon which goes brittle and breaks up after this period of time, irrespective of how it’s been ridden or maintained. To change the cam chain tensioners the entire motor needs to be stripped to the last nut and bolt which offers a great opportunity to really understand the history of the motorcycle and fix anything that requires attention. These motors require oil changes every 1,000 miles and filters every 2,000 miles with valve clearances checked at each interval. If the valves need adjusting, then it’s time to do them. Thinking you can just check them every 8,000 miles is really not acceptable and could cause the bike to drop a valve or two. These motors are very precise, they’re like a Rolex watch and if they’re maintained properly are a great high mileage engine. However, if the maintenance is ignored then the life of the motor is severely reduced. There’s more to these machines than the motor, although it was really all about the engine and the engineering when it came. The motor is just one of the reasons that these machines will end up breaking the £100,000 barrier in years to come for investment grade examples. Some bloke who makes tables but is well known in the CBX1000 owners club will not add value to your machine when it comes to doing this level of work.

Honda CBX1000 looking down camshafts
Buying camshafts for a Honda CBX1000 would be ridiculously costly if you can find them.

Removing a Honda CBX1000 rocker cover

Removing a Honda CBX1000 rocker cover is not as simple as just undoing the bolts and lifting it off once the motor is tilted forward. Although the cover looks like it will clear of the taco drive, it won’t. Remove the tacho drive first and ensure that the thrust washer shim is removed first, then the taco drive and then remove the rocker cover. Check that the oil seal for the taco drive is present in the rocker cover, as this and the shim are vital. We have just repaired someone’s CBX1000 cylinder head which had been re-assembled by a CBX1000 “expert” who failed to fit the shim and taco drive oil seal. Consequently, the taco drive leapt out of its housing and the cam lobe forced it through the cylinder head. Special care is also needed with the taco drive cam follower, as the ally is extremely old, becoming very brittle and it’s clearly under-engineered. Most of these motors require this component to now be reinforced with ally weld in a special jig and then dressing. Should this piece break, which they often do, there is a good chance that the taco drive will find its way through the cylinder head. This cam follower is not available and the original is best to be reinforced right now. Once all of this work is done now, the motor is good for another forty years.

Honda CBX1000 broken tacho drive
The taco drive housing has failed due to the age of the aluminium.
Tacho drive broken in 2
You can see the failed piece of cam follower.
Cracked tacho drive
The taco drive housing really is under engineered and requires reinforcement.

Honda CBX100 Cylinder heads

As soon Honda CBX1000 cylinder heads are removed, they need to be stripped completely with all valves removed and the guides need checking by an engineer. The head is split into two banks of three cylinders with twelve valves on each bank and a cam chain tunnel in the middle. At its thinnest point that cam chain tunnel is just 8mm thick and the head wants to bow. If the head is placed on a flat bed and just skimmed it will never seal correctly, so it needs to be taken to someone who understands these cylinder heads. We use Pete Willis Engineering in Tavistock, because he works for Formula One teams and understands the Honda CBX1000 cylinder head. The head is bolted down and then skimmed so that when it’s bolted to the block it will be truly flat. He checks the valve guides for clearance, as he has the equipment to do so, and has the equipment to cryogenically switch out the guides for new ones if necessary. The valves will then need very careful lapping and should not be over-ground or new seats will need to be cut, as it’s very cramped in these heads. The cylinder head washers will need replacing to prevent oil leaks and it is critical to use the genuine components rather than replica parts. We only ever buy our parts from Bert at The Six Center in Holland as we cannot trust UK suppliers who are putting replica parts in Honda parts bags. You can see below what goes into these cylinder heads.

Honda CBX1000 cams from above
The Honda CBX1000 has four camshafts each joined in the middle of the engine.
Honda CBX1000 engine rebuild.
The engineers blue shows where the head will start leaking.
Head skimmed
The cylinder must be skimmed by someone who really understands these heads.
Checking valve guides 2
All 24 valve guides must be checked by an engineer.
Checking valves themselves
All twenty four valves must be checked by an engineer.

Honda CBX1000 barrels

Honda CBX1000 barrels need to be checked for being true across the head mating surface, this is usually not a problem but has been known to be in some cases. Obviously, the bores, pistons, rings, ring gaps, little ends and big end bearings need to be checked. The bottom of the cylinder block and the crankcase mating surface to the block need to be checked for trueness. This is an area which is often overlooked but which can be problematic and can require skimming. We have rebuilt many of these motors and failure to check this really can result in tears, as now is the time for skimming if necessary. It’s a great time to change the two cam chains, as well as the two cam chain tensioners. All valve seals and gaskets need to be changed now.

Honda CBX1000 crank case Cylinder surface
The surface of the crankcase to the bottom of the barrels must be checked for trueness.
Honda CBX1000 engine laid out YES

Honda CBX1000 cranks and con rods

Honda CBX1000 cranks and con rods need thorough checking, especially the con rods as they are prone to bending. If leaky carburettor fuel shut off valves fill the cylinders with fuel the motor can suffer hydrolock. This is where the fuel cannot be compressed and the starter motor will bend the condos, usually on cylinders one and six. If you find bent con rods, then check that the bores have not been made oval. 

Honda CBX1000 bent con rod
Hydrolock will cause the conrods to bend.

Platsiguage the entire motor

All of the mains bearings and crankshaft need to be pastiguaged after being torqued back into the crank cases to ensure everything is within tolerance. If anything is at all out of tolerance, it is necessary to find the right new mains bearings and to grind the crank if necessary to bring everything back into specification. The cams all require plastiguaging once torqued down and bringing back into specification if anything is worn. Check all oil galleries are clear and replace all bearings and seals. The only bearing no longer available is the output shaft bearing, but everything else is still available along with all the seals. The oil pump needs to be stripped, cleaned and all shims checked while it is out of the engine.

Honda CBX1000 crankshaft
The entire crankshaft, oil pump and entire motor need to be measured with plastiguage.

Primary chain

Now is a great time to change the primary chain, as these are still available and are critical to safe running of the CBX1000 engine. The chain tensioner is actually oil fed and sits above the primary chain. There is a sort of nylon guide underneath the chain, but there is the hydraulic one above the chain itself. If the primary chain is too loose, it will saw through the hydraulic tensioner, which is one of the many reasons for the 1000 mile oil change intervals.

Oil change intervals

The oil change intervals are so frequent because the motor runs very fine tolerances and oil sludge will interfere with this. The cam chain tensioners and cam chains need fresh oil to keep them in top condition and the primary chain and tensioner need fresh oil to keep everything in good condition. Following the strict oil change regime is really obvious when you rebuild these motors and it’s not difficult to do. Many British and Italian motorcycles have similar regimes and are there to preserve the engine and ensure they deliver plenty of high mileage fun. There was a period when these motorcycles were outdated, undesirable and maltreated. Now is the perfect time to nurse them back to their former glory. As I stated in my article that Japanese classic motorcycle prices must increase, these iconic Honda CBX1000s are extraordinary motorcycles and are well worth doing the work to now. It will never cost so little as the price of parts, labour and servicing will never go down, they will only ever increase and the sooner this work is done, the less it will cost. Now is the time for a Honda CBX1000 engine rebuild as it is the best value time to do it and many of the parts inside these machines will just let go. 

Honda CBX1000 built from back NICE
Once the Honda CBX1000 motor is rebuilt, it is good for extremely high mileages if it’s serviced regularly.

Use of cheap parts

Use of cheap parts has played havoc with Honda CBX1000s and now some less scrupulous dealers are passing off cheap parts as genuine Honda. We’ve shown you what cheap fuel shut off valves can do to a motor, however genuine Keyster components will prevent this from ever happening. Yet again, be careful as some British dealers are palming off lesser quality fuel shut off valves for Keyster. Replica taco cables can cause the taco drive to damage its housing, so buy the genuine article. Once these jobs are done, these are great and reliable motorcycles. If they are properly looked after they are reliable, high mileage motorcycles, so ride them and enjoy them. A Honda CBX1000 engine rebuild is now a necessity which will last many decades and will force prices upwards. All of our Honda CBX1000s come with engines fully rebuilt by us and an unlimited mileage warranty for one year. There are many reasons why the Honda CBX1000 will end up going to over £100,000 for investment grade examples in the coming years and I will be writing further about this soon. If you want an investment grade Honda CBX1000, contact The Motorcycle Broker.

Paul Jayson


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