I'm going to do a timing belt job on my Honda Accord. My question is can I just buy, for example, an Aisin (OEM manufacturer for Honda water pumps) water pump from Egay and have it be the same quality as the dealer? Their part #'s match, but I notice slight casting differences.

Same stuff at a cheaper price or MUCH different?

Spanks.

 

Usually cheaper stuff is cheaper for few reasons. Wider tolerance is the most common since narrower tolerance increases manufacturing costs.

Materials is the next thing manufacturers make cuts on.

I've worked with expensive steel and i've worked with shitty cheap steel at my last job.

The most common issue with cheap steel is hard spots and a hard spot will definitely wear out the tool bit used to cut the part out much faster... many times it cracks the tool as well. If the tool is good enough many will leave it but then the finish will look.. scratched. If you were to replace the tool then it will leave a nasty lip where the old tool broke. Most machine shops that try to save every penny wont run the finishing cut more times than necessary. At last cheap steel with hard spots will have hard spots on one spot and soft elsewhere which makes it easier to crack depending on the load especially if heat treated. I know that first hand.. had to have surgery on my palm because a cheaply made sleeve shattered and a sharp piece went into my hand. High quality steel on the other hand cuts like butter.

Ground parts will get rid of the machining marks as long as the tolerances are good.

 

There's nothing wrong with Aisin. Just did a water pump on an 05 Legacy GT Turbo, did exactly what you're proposing (and have been on many cars for a long time)....Its got "Japan" stamped on it, looks and feels great, all gaskets and bearings are high quality, and works perfect.

And for 1/3 the stealership cost

 

Trademotion and RockAuto can sometimes hook you up with OEM stuff from out of territory stealerships and prices are comparable to eBay etc.