Crank Rods Big End Blog and tips

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Crank Rods Big End Blog and tips

Postby Gman » Sat May 05, 2012 11:02 am

My engines have been rebuilt by me from the crank up.This is just a general blog on how I did it and things I used.THe Crank case carcase MUST be spotless inside and free from ANY debris metal or otherwise.

1:Crankcase carcases were either Vapour blasted clean at an engine cleaning company(Yellow pages) or with my Car power washer in my garden.I broke down any oil deposits with WD40 type stuff,then Carb/Brake cleaner and finally compressed air to dry and blow through every and all orifices.
I then,"Glaze Bust" the cylinder walls.Google,"Glaze Busting) but I do it manually,not with the specialist tool.

2:I have never had to replace the main bearing white lining shells as even on the worst seized engine these were not damaged.It's the Big end bearing/shells that seem to get destroyed,not the main bearings.If you do have to replace the main bearings refer to the manual/s as there are two shell sizes to fit two different crank case hole diameters but you can basically use any CX/GL 500 crank as the crank outer end ODs remain the same.

3:Because of the,"V" design it's a bit harder to put the Pistons and rods in without damaging the soft metal Crank faces so I have the Crankcase upright for each side so the rods are going in with the Piston compressor straight down and take ULTRA care not to let them sore the crank as this will ruin the crank shaft.

4:I mark one side of the crank caps to I know which way round they fit when putting in as they are Asymmetrical and once on the Con rod studs are a PITA to mice up and down.

5:When I take the gearboxes out I keep them together using some masking tape wrapped around them as they are PITA to reconstruct correctly e.g getting all the thrust washers and dogs and gears in the right place.Even cross referencing the drawings in the manuals,it's hard.

6:Once you have the Crank end cap and gearbox/transmission in then follow the normal rear end procedure for fitting the A/C flywheel and Gear linkages again triple checking with the manual that ALL components are there including the 3 thrust washers e.g one either side of the small reduction gear and axle and one under the left hand side gear change mechanism.
Before replacing the A?C Flywheel Double check that you have the Cam chain timing as per the drawing in the manual or on forums. ... imebig.jpg

Hone the tapered end of the Crank shaft with some 500 wet and dry paper so it's polished.This will allow the A/C flywheel to be torqued down correctly.You need to get it close to it's top Torque value of around 70 Ftlbs.
The engine will need to be,"Locked" to do this.There's more than one way of doing this but here's a couple, ... nklock.jpg ... Lock-1.jpg

7:Don't button up the rear engine cover until you test that the gears operate.Present the rear case to the engine taking care not to damage the Water pump engine side oil seal with the Cam shaft as it goes through and go through the gears by twisting the main shaft and operating with the gear lever on.When satisfied you can take it off,fit the gasket(The gasket cannot be left off as it sets the correct distance for the rear cover.If left off it will bind the engine and can cause the Stator to be damaged.

Note the correct positioning of the Main drive shaft small driven gear,


The teeth go INTO the drive shaft,not against the engine.This is very very important.

8:Once you are satisfied all is well and you refit the engine the cooling system MUST be bled as per,

and then the engine left to cool and the Cylinder head bolts torque re-checked.Important! and then again check them after a couple of hundred miles.See this video for more Cylinder head information,

9:Running in.
Even if the cylinders have not been r-bored but you have used new rings you should run them in.I have used this method,

and then taken it easy not going above 5,000 rpms for about 100/150 miles just to make sure everything gets run-in smooth.Then I change the oil and filter again to get rid of any metal debris that may have been worn off the cylinder walls by the new rings.Oil and filters are cheap if you use the 10w40/15w40 diesel engine oil many of us use on these bikes.

Finally always re-check the torque on the head and frame engine bolts etc again and the tappets just for good measure.As hopefully you won't be touching then engine again until you say replace a cam chain getting all of the above right will give you 50k plus miles with no problems.
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Re: Crank Rods Big End Blog and tips

Postby nicktylermo » Wed May 30, 2012 2:12 pm

I find it very helpful to cut two small pieces of fuel hose and put them over the rod bolt studs before dropping in the rod and piston. This creates a peace of mind as it will protect the crank journal from getting scratched. You can then just use pliers to pull of the hose pieces down below before assembling the bottom caps. (step three)
Also, when torqueing down the a/c flywheel, I used a regular 3/8" ratchet with a 17mm bolt on the front of the crank and let it rest against one of the front long engine mounting studs to lock the crank while using a torque wrench on the rear a/c flywheel side. This kills two birds with one stone as the front crank bolt torque is supposed to be the same as the rear. So both crank end bolts get torqued at one time. (step 6)
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Location: Cape Girardeau, Missouri. U.S. (1980 cx 500 custom, 40,000 miles)(1972 Honda cb100, 5,900 miles)

Re: Crank Rods Big End Blog and tips

Postby Gman » Wed May 30, 2012 3:36 pm

Great tip :mrgreen:

I'll use that myself next time :D
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