Rebuild of Bottom End

[Austin Miller]

Hey guys, so this might be a no brainer but I want to be sure about this. We are rebuilding the bottom end of the motor (03 GSXR 600) and there is some discussion on whether or not we need to replace some parts.

I think all of these are crucial, so let me know what you guys know.

First off, we bought the main journal bearings but we are debating whether or not to buy the rod bearings. This seems obvious to me. We need to buy them, since we are down there might as well do it.

Additionally, I think we should replace the thrust bearings. Im not sure if this is super important, but again, since we are down there, I feel it should be done.

Finally, what do you guys know about the piston pins? Does that need to be replaced? What about the retention clips for that pin?

[Austin Miller]

Hey guys, so this might be a no brainer but I want to be sure about this. We are rebuilding the bottom end of the motor (03 GSXR 600) and there is some discussion on whether or not we need to replace some parts.

I think all of these are crucial, so let me know what you guys know.

First off, we bought the main journal bearings but we are debating whether or not to buy the rod bearings. This seems obvious to me. We need to buy them, since we are down there might as well do it.

Additionally, I think we should replace the thrust bearings. Im not sure if this is super important, but again, since we are down there, I feel it should be done.

Finally, what do you guys know about the piston pins? Does that need to be replaced? What about the retention clips for that pin?

[Peter7307]

This really is an item by item situation but as a general rule if one part is worn enough to be replaced then it is good practice to replace all related bits.

Consult your workshop manual and use a micrometer to see how much wear is present. An oil pressure gauge will also help indicating with bearing wear.

Personally I would replace all the bearings.
The piston pin is normally a long serving part but as above I would also check the item against the manual specs.

Intended life and costs also factor into this equation.

Cheers , Pete.

[VFR750R]

Judging bearing wear is not a difficult job, if they look good, they probably are. That said, it is always wise to check clearance through the method discribed in the rebuild manual. Some people sware by plati-gauge, others say its worthless, but using micrometers and bore gauges sets an inexperienced rebuilder up for trouble. Real clearance can be as much as .0002" tighter then what you read due to the bore gauge digging into the bearing material. But, it depends on the bore gauge and the hardness of the bearing material on exactly how much. Some hondas are as tight as .0008 clearance, and with another .0001 error in both gauges you could get down to .0004!! Might work if you preheat the water before starting every time.

It wouldn't hurt to learn to use both and compare the results.

Wristpins last forever, wristpin clips should be changed anytime they are removed...luckily they're cheap. Also, look at the wristpin bores in the pistons for wear/eggshaped deformation. Probably doesn't occur very much in motorcycle engines but it's more likely then wristpin wear.

[Brian Evans]

Piston pins are normally fitted to the pistons and the rods, either by honing the pistons and rods or by select fit. So don't replace them unless you are replacing the pistons and prepared to do work on the rod small end bushes. If you don't take the pistons off the rods then you don't have to worry about circlips, but if you take them off use new circlips to reassemble.

If you're in there anyway, replace everything that wears. All the bearings, and maybe the timing chain, timing chain tensioner, that sort of stuff.

The only time you wouldn't replace the bearings is when you are terminally cheap, or the engine is just open for a look-see after a dyno session. Although I'm sometimes known to leave in old thrust bearings if they look perfect and crank end play is exactly where I want it to be.

Brian

[Davidimurray]

You may want to consider why you are rebuilding the bottom end as to what you do. For example, if this is due to minor oil starvation, you may want to check the top end over for any sign of bucket wear/scoring. If you've had heavy oil starvation then I would definitely check the head over and even possiblly check the bores.

[VFR750R]

One more thing, regardless of if you decide to replace your bearings, make sure you follow the torq specs exactly on the rod bolts and cases. including thread lubricant!

[Brian Evans]

One other thought - find out if the rod bolts in the engine are considered reusable. Many stock rod bolts are not, or are marginal. Cheap insurance to throw in a new set of ARP rod bolts in any case.

Brian