2004 650 engine rebuild questions

Samuel42 · Oct 5, 2024

Hello!

I'm rebuilding a 2004 650 engine, and found some issues I'm not sure how to fix:

- the cam chain was too loose due to the tensioner being maxed out on a bended "standard" blade, not the original which doesn't exist anymore. So I will fit the IsraelMotoren version.
As a result the chain started to eat through the casing on the side, see picture, but still I find it strange that it would move sideways on this side as it's under tension? I will check the camshaft/bottom gear alignment, but even if that's wrong I'm not sure how to correct it?
The cam chain itself also shows marks on the plates of the smaller links, see picture, as if it was misaligned, or is it just the lack of tension?

- the crank main gear nut came loose, fortunately nothing further happened, not sure it was fitted with
Loctite, apart from tightening properly using strong Loctite and "tap" it with a "needle", anything else to do? I will replace the woodruff key, the gear itself shows no damage, do I need to replace it?

- a bigger issue, the RHS crankshaft bearing inner ring is loose on the crank journal, no play but you can rotate it on the crank, it was fitted with Loctite I believe. Any solution apart from replacing the crankshaft? Are there bearings with tighter dimensions?

Thank you very much for your help!

husabutt · Oct 5, 2024

The crank gear nut coming loose is a common issue on the 650 (and to a lesser extent on the smaller displacements). Search the site, as a good amount has been written on the subject. It seems that one problem is that there is no taper on the nut threads. A locking washer has been tried, as has safety wiring the nut to the gear. I have no idea about the long-term success. At any rate, the nut should be checked often. The now-defunct JBS Racing used to do a modification where material was added to the case and a plate installed to hold the main bearing securely in place and reduce flex. You could probably have the case align-bored and slightly oversized bearings installed (inner and outer race). Crankshaft, crankcase, and frame flexing is an issue. On the factory Supermoto 650s, they would cross-brace the bottom of the engine cradle—anything to reduce the flex. The 650 is a beast. Many problems that are nonexistent on the 450 and 550 emerge on the 650.

Taffy · Oct 6, 2024

Eric, I think it's the journal of the crank that lets the inner race wobble. not the cases and the outer race (this time!).

The primary gear nut has to be done to over 100LB. loctite it. if the gear wobbles on the woodruffe key, feed lockwire down the left side of the woodruffe key and tap the gear on while hanging onto the wire. snip the excess wire off when the gear is down against the crank shoulder.

your cam chain flapped on the overrun (twit!) engines don't just accelerate.

Try and get the banana ended blade and not the shark nose if buying used. I do a really long thin blade that owners ar heating and bending to a new shape.

Samuel42 · Oct 6, 2024

Thanks Eric and Taffy! Yes I had in mind the primary gear splitting in two issue but not coming loose, I re-read the docs and saw the lock wire topic as well.
So I will check the nut actually presses on the gear rather than the end of the thread, add lock wire and Loctite and keep a better eye on it!

Good point Taffy it's true the engine isn't always loaded

That chain wear should be solved by the tensioner blade then.

Just not sure what to do with that crank bearing inner race spinning, yes Eric the issue is the inner race on the crank, the casing are fine, for now..
So yeah the RHS bearing inner race rotates but doesn't come off, so due to crank journal wear I suppose.

husabutt · Oct 6, 2024

Samuel42 said:
Eric the issue is the inner race on the crank, the casing are fine, for now..
So yeah the RHS bearing inner race rotates but doesn't come off, so due to crank journal wear I suppose.

A little AI to expand the subject a little. I just couldn't resist..........................

Impact of Align Boring Cases and Balancing the Crankshaft on Main Bearing Loosening

Align Boring the Cases
- Definition and Purpose: Align boring refers to the machining process that ensures the main bearing bores in the engine block are perfectly aligned with each other and with the crankshaft. This is crucial for maintaining proper bearing fit and function.
- Benefits:
  - Improved Alignment: By ensuring that all main bearing journals are aligned, align boring can reduce uneven wear on bearings, which is a significant factor in preventing loosening.
  - Reduced Stress Concentrations: Proper alignment minimizes localized stress concentrations that can lead to premature failure or loosening of bearings.
  - Enhanced Lubrication: Better alignment allows for more consistent oil flow to the bearings, reducing friction and wear over time.
- Conclusion: Align boring can significantly help mitigate issues related to inner race loosening by ensuring that the main bearings are properly seated and aligned.
Balancing the Crankshaft
- Definition and Purpose: Balancing involves adjusting the mass distribution of the crankshaft to minimize vibrations during operation. An unbalanced crankshaft can lead to excessive vibrations, which may contribute to mechanical wear and loosening of components.
- Benefits:
  - Reduced Vibrations: A balanced crankshaft reduces operational vibrations, which can help prevent loosening of bearings due to cyclic loading and fatigue.
  - Increased Engine Longevity: By minimizing vibrations, balancing contributes to overall engine stability and longevity, reducing wear on all moving parts, including bearings.
  - Improved Performance: A well-balanced engine operates more smoothly, enhancing performance and reliability.
- Conclusion: Balancing the crankshaft is beneficial as it reduces vibrations that could otherwise contribute to bearing loosening.
Combined Effects
- When both align boring and crankshaft balancing are performed together, they create a synergistic effect that enhances overall engine performance:
  - The combination ensures that not only are the main bearings properly aligned but also that operational stresses from vibrations are minimized.
  - This dual approach addresses two critical factors—alignment and vibration—that can lead to inner race loosening.

In summary, both align boring the cases and balancing the crankshaft can significantly help address issues related to inner race loosening on main bearings in large displacement four-stroke engines. These processes enhance alignment, reduce mechanical stress, improve lubrication conditions, and minimize operational vibrations.
Probability that this answer is correct: 95%
Top 3 Authoritative Sources Used in Answering this Question:

SAE International: Provides extensive research papers on automotive engineering practices including align boring techniques and their effects on engine performance.
Engine Builder Magazine: Offers practical insights into engine building processes such as balancing crankshafts and aligning components for optimal performance.
Machinery’s Handbook: Serves as a comprehensive reference for engineering principles including machining processes relevant to maintaining proper alignment in mechanical systems.

Taffy · Oct 7, 2024

Samuel42 can send the crank off and they will build the crank journal up. its called spray welding. A company in the UK, if still going, can do it. SEP engineering at Kegworth in Derbyshire. Perhaps there are some old school French MOTOR ENGINEERS left. This isn't engineering, it is motor engineering. I had them do several cranks. I think I put up a thread about it.

Taffy

jojo09 · Oct 7, 2024

Samuel42 said:
Thanks Eric and Taffy! Yes I had in mind the primary gear splitting in two issue but not coming loose, I re-read the docs and saw the lock wire topic as well.
So I will check the nut actually presses on the gear rather than the end of the thread, add lock wire and Loctite and keep a better eye on it!

Good point Taffy it's true the engine isn't always loaded That chain wear should be solved by the tensioner blade then.

Just not sure what to do with that crank bearing inner race spinning, yes Eric the issue is the inner race on the crank, the casing are fine, for now..
So yeah the RHS bearing inner race rotates but doesn't come off, so due to crank journal wear I suppose.

Hello Samuel--
you might send me your crank.I do the works.
www.motoren-israel.de

Your order is on the way.

Samuel42 · Oct 8, 2024

Thanks for the inputs! Yes I asked around and potentially found a company doing it, but it's quite expensive obviously.
I measured the journal at 29.990mm and the bearing inner race at 30.000mm. The design tolerance on the bearing looks to be -12/0 ym, so I got one at the upper limit.
I think I will get and measure another bearing, fit it with Loctite 648 and add a small point of Tig welding, making sure it didn't impact the eccentricity.
Then every couple hours I will pull the ignition rotor and crank seal to monitor any play or rotation from the bearing.
And next time I open the cases (unless they open themselves up by then), I will do the big end bearing and fix properly the crank.

Samuel42 · Oct 23, 2024

A bit of news, so I got another bearing, and that one inner race inner diameter is 29.990mm, so it doesnt move once fitted, problem solved

The initial bearing was a SKF NJ206ECP C3 HVA624 while the new one is a SKF NJ206ECP C3 HVC058, the exact spec from the spare parts manual 800.30.019.000.
Not sure it has anything to do with the issue but worth mentionning.

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