Motor rebuild or replace?
Joined: Sep 2007
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Joined: Dec 2016
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Why so hard to rebuild?
A rebuild is a huge gamble. The risk is extremely high that it'll grenade on you. These motors just don't take well to rebuilds.
You could easily spend several thousand, and end up in worse shape than you are now.
There is virtual zero chance that your mechanic can rebuild this motor successfully. Nor zero chance that machine shop he always uses for rebuilds and has never let him down can do it either.
You need to have a specialist shop that has a lot of experience rebuilding these motors do it, and even there you'll find plenty of horror stories.
There are also horror stories with new assembled blocks from Honda. Apparently they weren't stored properly or maybe the substance used for assembly lube wasn't meant to sit around for decades before engine was ever fired up. Whatever the case, stories of new engine after new engine failing in a few hundred miles after install.
You could sell the motor as-is for someone else to gamble a rebuild with, or someone that wants to sleeve it for a forced induction build (sleeves are cast iron cylinders that get pressed in to replace the stock frm impregnated aluminum cylinders. Cast iron can better withstand high levels of turbo boost that the really high hp guys go after. But its not at all a good choice for a car that isn't running super high boost).
Then buy a used motor. Yes, its also a gamble, but much less of one. If you get an ap2 motor, its highly likely not to burn oil, or at least a whole lot less than a used ap1 is likely to do (Honda changed how they build the ap2 motors, which largely fixed oil burning issues).
You could easily spend several thousand, and end up in worse shape than you are now.
There is virtual zero chance that your mechanic can rebuild this motor successfully. Nor zero chance that machine shop he always uses for rebuilds and has never let him down can do it either.
You need to have a specialist shop that has a lot of experience rebuilding these motors do it, and even there you'll find plenty of horror stories.
There are also horror stories with new assembled blocks from Honda. Apparently they weren't stored properly or maybe the substance used for assembly lube wasn't meant to sit around for decades before engine was ever fired up. Whatever the case, stories of new engine after new engine failing in a few hundred miles after install.
You could sell the motor as-is for someone else to gamble a rebuild with, or someone that wants to sleeve it for a forced induction build (sleeves are cast iron cylinders that get pressed in to replace the stock frm impregnated aluminum cylinders. Cast iron can better withstand high levels of turbo boost that the really high hp guys go after. But its not at all a good choice for a car that isn't running super high boost).
Then buy a used motor. Yes, its also a gamble, but much less of one. If you get an ap2 motor, its highly likely not to burn oil, or at least a whole lot less than a used ap1 is likely to do (Honda changed how they build the ap2 motors, which largely fixed oil burning issues).
I've seen this comment many times and I have wondered what makes an S2000 engine so hard to rebuild? I can guess that the high redline makes getting the balance correct could be difficult, but I've never heard the same issue on an RX-7/8 rotary that has a higher redline?
Joined: Aug 2012
Posts: 8,755
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Rotary doesn't reciprocate, it just goes round and round (ok, it goes round eccentrically, so its not like a gas turbine to truely just goes round). Therefore much less stress.
What makes it tricky is the frm coated cylinders, which can only be bored a very small amount, and only in certain circumstances, which very often isn't what happens. These walls also don't like to be honed. Only certain piston coatings are compatible.
Then there is the multiple piston and bearing sizes. To get the tight tolerances needed, every bore in block was carefully measured, and then a piston size to best fit tbat bore determined, and stamped into block. So virtually all F motors don't have the same piston part numbers in all 4 holes. Its like introducing S, M, L sizing in a one size fits all world. No off the rack suits here. The sizes were called A, B, etc.
The same custom sizing protocol extends to the crank and rod bearings. Different size shells in each location based on block, crank, and rod sizing of those components in that motor. Even the upper and lower shells can be different sizes.
When an engine is rebuilt, you typically resurface parts like crank journals, by polishing them (or in many cases, machining them). When you polish, will the same size bearings still give the same clearances? What if crank is machined, what size to use then?
Combine all this with the stress of 9k rpm, and you have a recipe for rebuilds that don't survive.
Even the shops that specialize in rebuilding these motors have had issues where one rebuild after another keeps failing for the same customer. The instance I'm thinking of it turned out a bad head kept ruining the blocks, but it took many cycles of new motors to finally get to the bottom of it.
What makes it tricky is the frm coated cylinders, which can only be bored a very small amount, and only in certain circumstances, which very often isn't what happens. These walls also don't like to be honed. Only certain piston coatings are compatible.
Then there is the multiple piston and bearing sizes. To get the tight tolerances needed, every bore in block was carefully measured, and then a piston size to best fit tbat bore determined, and stamped into block. So virtually all F motors don't have the same piston part numbers in all 4 holes. Its like introducing S, M, L sizing in a one size fits all world. No off the rack suits here. The sizes were called A, B, etc.
The same custom sizing protocol extends to the crank and rod bearings. Different size shells in each location based on block, crank, and rod sizing of those components in that motor. Even the upper and lower shells can be different sizes.
When an engine is rebuilt, you typically resurface parts like crank journals, by polishing them (or in many cases, machining them). When you polish, will the same size bearings still give the same clearances? What if crank is machined, what size to use then?
Combine all this with the stress of 9k rpm, and you have a recipe for rebuilds that don't survive.
Even the shops that specialize in rebuilding these motors have had issues where one rebuild after another keeps failing for the same customer. The instance I'm thinking of it turned out a bad head kept ruining the blocks, but it took many cycles of new motors to finally get to the bottom of it.
Joined: Nov 2008
Posts: 199
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From: Seattle area
^^^ Sums it up pretty well.
These things are freakishly sensitive to machining error, blueprinting/measuring error and tolerance stack. Imagine having to be accurate to 0.0001" everywhere. Garden variety engine of the era you'll probably find yourself working in the 0.001" range. Not here.
Ditto the previous comments regarding ECU selection and valve adjustment. OP, ensure your new engine's health with a valve adjustment the sooner the better if you haven't already.
These things are freakishly sensitive to machining error, blueprinting/measuring error and tolerance stack. Imagine having to be accurate to 0.0001" everywhere. Garden variety engine of the era you'll probably find yourself working in the 0.001" range. Not here.
Ditto the previous comments regarding ECU selection and valve adjustment. OP, ensure your new engine's health with a valve adjustment the sooner the better if you haven't already.
Joined: Aug 2012
Posts: 8,755
Likes: 1,858
That opens a whole new, larger can of worms. For a variety of reasons, iron sleeved blocks are really only good for extreme hp builds that need the strength, and that will see low (albeit intense) miles, and more frequent rebuilds.
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