SOHC.co.uk Forums > CB500/550
CB550k1 US Import - UK registration
McCabe-Thiele (Ted):
Someone here will know the best engineering solution, Timesert, Helicoil or your solution.
Not sure if a deeper thread would change the loading on the top casing in some way that was undesirable.
K2-K6:
You need to be careful in judging just what you have and the design that's been used originally in these crankcase.
Having a case/casting hole that has a tapped thread right up to the surface is simply a different design to one that uses a clearance bore first with the thread deeper inside the casting (the top threaded type tries to pull the surface up at the gasket, making distortion more likely) with the deeper type design aiming to avoid this.
Accuracy in understanding, with input from those on here having relevant experience of that engine, is key to understanding if it's actually damaged or designed like that in the first place.
Bolt length is absolutely critical on these, as it is for many tightly designed structures.
juitz:
--- Quote from: K2-K6 on December 11, 2022, 02:28:26 PM ---You need to be careful in judging just what you have and the design that's been used originally in these crankcase.
Having a case/casting hole that has a tapped thread right up to the surface is simply a different design to one that uses a clearance bore first with the thread deeper inside the casting (the top threaded type tries to pull the surface up at the gasket, making distortion more likely) with the deeper type design aiming to avoid this.
Accuracy in understanding, with input from those on here having relevant experience of that engine, is key to understanding if it's actually damaged or designed like that in the first place.
Bolt length is absolutely critical on these, as it is for many tightly designed structures.
--- End quote ---
Totally agree which is why as always, asking the experts.
My casings have a clearance section followed by thread. Given the load is tensile as the bolts are trying to pull the two halves together, I think the key item is to ensure the bolts have enough / same number of engaged threads to not overstress the bolt when tightening these up to approx 23Nm as per manual.
Having said that, feel like I'm missing or overlooking something here 😉
K2-K6:
Apologies if any confusion as it's people like Bryanj and Oddjob that have more intricate/specific knowledge than I for these engine sizes (550) to help.
General assessment though, put the corresponding bolt in through clearance crankcase side with correct washer etc, then mark (white paint) where it protrudes from face of casting and facing the other case half.
Then put that bolt into it's thread location such that you can only just feel the thread's at their very start. Now measure the distance between that original mark and the crankcase face to give you the distance the threads are now going to engage when they would be fully tightened. That figure in general fastener design should be at least 1.5x bolt diameter to take expected load. So a 6mm bolt would need 9mm of engagement as minimum, etc for different bolt diameter.
This effectively measures by deleting the "counterbore" section to let you judge each one individually.
As mentioned, this is general engineering principle (that thread engagement length multiple) but with the provisos that there just may be some slightly different in these engines.
The risk is pulling threads out of the aluminium case without enough engagement, rather than risk to steel bolt.
juitz:
Bit of a loss at what to do now.
120mm length bolts don't work and taking some measurements I only have about 6mm of available thread to engage.
I'm thinking keen-sert is probably only option.
I can't replace the cover as this has the engine number stamp on it.
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