Discussion and questions related to the course Practical Engine Building
I am about to tackle my first rebuild as my sr20 seems to have developed early stages of rod knock (fingers crossed it’s not too bad).
I am considering reusing the pistons and rods only replacing the rings based on the assumption that they are in good condition and wondering whether this is a wise move? Is there any particular spots/things you suggest to look out for? Assuming they are all good (this maybe a dumb question) I wouldn’t need to worry about balancing and could essentially light hone and install?
You are making assumptions before inspection. If you have inspected the components and they are within spec, or can be recondtioned then you decide if you are going to re-use them.
In theory, probably, but as David suggested, until you actually know what you're dealing with you shouldn't make assumptions.
When you do strip the engine down, pay careful attention to what you find - an engine doesn't usually develop a 'knock', or other problems, without an underlying cause.
Thanks guys. Understood I’m jumping the gun a bit here. I’m running a stock sump and the cars a drift car. My theory is that potentially the oil pick up pulled air and air rated the oil which in turn caused this. I’m probably completely wrong lol.
Will come back to you with my findings to get a second opinion.
Have pulled apart engine and bearing on cyl 3 is well done. Crank looks ok but will organise to crack test and linish. Not sure what may have caused this yet though.
I have attached photos of pistons which don’t look the best. Looks like maybe detonation or something? But seems to be old damage. I’m running e85 now so shouldn’t be an issue moving forward.
With OEM rebuild and piston grades does it matter if I interchange these? Long wait time to get my hands on new OEM ones so wanted a second opinion on using a second hand set that are in decent condition but may not be same grade as the originals.
My thoughts - and you should definitely get opinions from those actually viewing the engine.
The crank journal may be OK, with a polish, as it looks fairly light and it isn't the full width of the shell - but your machine shop, if they're good, will be better informed to tell you.
Pistons show what seems to be quite a lot of oil burning but, more to the point, they all seem to show signs of debris going through the engine. The bores appear to be OK, with some rub marks where debris has deformed the piston edges, but nos scoring or scuffing seems evident - NOTE, damage can be difficult to spot with such photo's, so do get a second opinion.
Second hand pistons may not be any better condition than those you currently have but, should you use that option, I don't expect grade to be a concern as there will be some bore wear - but you should always check, anyway. I don't see any point in worrying about that at this point, untill you remove them and see what condition they're actually in. You may even wish to consider a rebore, with forged pistons, if you're driving the vehicle hard, asd that will give you the best fit, compression and oil control.
I’m moving onto forged piston and rod combination with the build. In the process of choosing what piston/rod combination to use and since deciding to go forged is there any significant benefit of going arp main studs?
I am trying to be budget conscious where it’s smart to be and considering reusing the stock main studs. My understanding is that these are torqued to yield but have heard people reusing them in the past. My power range will be between 300-400hp.
Why would you re-use a fastener in a 300-400 hp build, when the factory service manual says "replace" (because it's a torque-to-yield design). You have to do at least what a stock engine would require -- no shortcuts there.
In your initial post you indicate you are rebuilding this because of a knock. I would expect that would have stressed things like main cap studs, and rod bolts -- and they would be inspected (potentially crack tested), or just replaced as a matter of course.
I didn’t even bother to check the service manual (whoops!) lol. Thanks for the response David.