Topic: CB750K bearing and crankshaft excessive wear after replacement of bearings

[DanishZebra]

I replaced bearings as part of my engine rebuild. The motor ran for <100 km when I found an oil leak coming from the cylinder head fins, I eventually tracked this down to a failed rocker cradle, likely due to grit from the hydroblasting that I found in the oil jet under the rocker cradle. It has now been cleaned out and i've cleaned out the oil galley.

With the engine out, I took this as an opportunity to also double check for any excessive wear in the bottom end as I had this feeling in my gut that there could be other blockages.

Upon splitting the case I inspected the bearings and to my horror have found the brand new bearings (green) I installed have been severely worn, and the crankshaft has severe grooving where as prior to the rebuild there was none.

I used a micrometer and determined that the green bearings were appropriate, so am wondering if anyone has any ideas of what went wrong? Are these photos indicative of bearings that were too thick?

Finally, are these bearings and crankshaft beyond using?

[Nurse Julie]

That has without doubt all been caused by blast media going around the engine with the oil. The engine needs stripping fully again, all blast media removing from oil ways and inspected for other damage caused. You need to pay particular attention to the crank and camshaft as these parts may well be damaged beyond use. All that damage could have been prevented, you only need one little grain of blast media going around an engine for it to be wrecked. Never, ever use blast media in the bottom end.

[newday777]

Ouch!  :'(
Did you do your own hydroblasting? That sounds like the cases weren't properly washed out with high pressure right away.
Unfortunately the crank is toast now along with the cam and cam holders.

[newday777]

If you are going to reuse the bottom end, check all the bearings for roughness and all oil ports for stuck media.
In other words total strip down and inspect everything.

[bryanj]

Typical shell markings of contaminated oil

[MauiK3]

You've got a job there to clean the oil passages.
The bearings are not usable, the crank, after polishing, might be if it measures ok, can't tell from photos.
Have to use a good micrometer, verniers are no where near accurate enough.

[PeWe]

I should take everything apart and clean it with a pressure washer after spraying with degreaser insode all oil channels.
Make sure to cover and catch the rubber plug sitting in lower case beside the gear shifter parts. Engine needs it.
A good powerful wash to make it all clean.
The oil holes might been full with media. Oil filter should not have it since it get oil direct from pump that get it from oil tank.

A bigger problem if oil filter has  grinding media. And top end.

[Don R]

 I'm sorry to hear that.

[Tim2005]

If I'm seeing that crank wear correctly, that looks seriously bad to me. Maybe strip and clean everything, especially check the oil pump itself too, but at this point I'd be thinking about abandoning ship and putting another motor in. By the time you've potentially replaced crank & all it's bearings, oil pump parts, every gearbox bearing and bush, all 3 chains, and so on, a good s/h motor may be a better bet

[Ujeni]

Sorry this happened. Not fun. You were wise to investigate past the top end.

As others have said, that is consistent with oil contamination. The bearings are toast and the crank journals are likely gone as well. Personally, I would have the crank replated or replace the crank. I doubt those journals can be polished out and, even if they could, you would have very thin plating on the journals afterwards.

A good winter project. Go through the rest of the engine and look for wear. Good luck! You aren't the first to do this, so don't beat yourself up over it.

[DanishZebra]

Thanks everyone for the inputs.

The hydro blasting of the top and bottom ends was done professionally. I will take it on the chin that I should have cleared out and inspected all oil passageways for blast media. A very expensive lesson learned from my first motorcycle engine rebuild.

The scoring on the crankshaft is beyond what I would be comfortable putting back in to the motor, there is a noticeable lip when I run my nails across it. One of the camshaft cradles is toast as the aluminium has melted and blocked the oil passageway. The camshaft looks "ok" with two small groove marks but i would prefer replacing.

Next steps for me is to measure up a few spare cranks I have to see which one is still serviceable. I will then remeasure and order bearings, and source a new camshaft and cradles ($600 AUD yikes)

Questions I have:
1. What is the best method to clear out oil passageways?
2. Must I use a matching camshaft and cradle or are these parts able to be mixed and matched?
3. Once motor has been reassembled, what is the best way to test if I have been successful getting all the blast media out before having a repeat of this incident?


Thanks

[bryanj]

Cleaning is clean, clean, clean and clean again, possibly brake cleaner, brushes and air.
Cams and towers are mix n match
There is no real way on making sure its clean as the oil ways that had crap in them are after the filter

[PeWe]

Rod bearings must be involved too?
Complete crank with rods are rather common on eBay.

Cam holders sometimes for a good price, sometimes not.
Some  look bad with horrible rocker arms with worn chrome.
Good to have a set or 2 extra.

[greenjeans]

Sorry man, that has to be a kick the junk.
As PeeWee states, probably gonna need rod bearings too.  As far as cleaning, I'd powerwash thoroughly, then I'd try and soak it some how.  If you could find an ultra sonic cleaner that could fit the cases etc.  do that.  Then, do it again.  Then, powerwash it again. It can't get clean enough.  Hang in there.

[Ujeni]

It is probably safe to assume that any surface that is built to a tight tolerance is at risk. Here's a list (I am sure other will add to the list):

• Connecting rod shell bearings
• Transmission bearings
• Oil pump
• Cam shaft
• Cam towers
• Valve guides

Again, I'm sure there are more tight-tolerance areas that are at high risk. These are off the top of my head.

Some areas of the engine likely won't be damaged beyond repair. Transmission gears, for example, will probably be fine after a good cleaning.

Something to consider is sealing the inside of the engine cases with Glyptal. I have done this for every engine I have rebuilt with 100% positive results. Many engine builders have been using this for a long time. If there are tiny particles stuck on the inside of the engine cases, they may not come out even with cleaning. Glyptal would seal them in place in addition to all the other benefits that it provides (faster internal oil flow for example). Keep in mind that Honda coated the inside of the sandcast engines with some kind of coating for the same effect. The process is very simple:

• Completely disassemble the engine cases
• Clean thoroughly. Then clean it again!
• Make sure the cases are totally dry. Zero water or residue anywhere.
• Apply Glyptal to the surface of the interior of the engine cases with a brush. Wear a mask and be in a well ventilated area. Don't apply at mating surfaces or in holes. You can wipe away excess Glyptal with Acetone.
• Allow it to air dry for a few days.
• Reassemble!

[DanishZebra]

Update for the forum,

Measured the crank and it is definitely toast. Fortunately I have a spare one that is still within tolerance. Interestingly the conrod bearings had no sign of wear......however I will get new bearings for both crank and conrods. I didn't see any excessive wear on the cylinder bore, pistons, transmission and so on. It seems to have only impacted my crank and journals.

I will be spending a few days cleaning out every single orifice multiple times, and hitting everything with the power washer.

Does anyone have any leads on a matching crank and cradle set? I found a few here in Aus and they are $600. ouch.