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Problems with B21A1 -> B20A3 swap

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Old 01-19-2017, 03:28 PM
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Problems with B21A1 -> B20A3 swap

I have a 1990 Prelude 2.1 Si. Its stock B21A1 was smoking and couldn't pass CA smog. I couldn't find a B20A JDM (called 16 places, got same message from everyone: we almost never see these anymore), and didn't want to spend the $4K I was quoted for a rebuild ($3K for engine, $1K for installation). So I found a mechanic who had a B20A3 he said was in good condition, and who charged me only $1K for everything (engine + installation). Note that even though he put in a B20A3, he only used the block, timing belt, and water pump from that engine, so it's still fully fuel-injected, with 4 valves/cylinder. The car passed smog, but I'm having issues with the new engine:

1) Loud buzzing sound from engine. I need to wear earplugs for extended highway drives.
2) Inconsistent idle (750 -1250). When it's idling at 750 (in drive, brake on) the car shakes strongly (you can see the steering wheel bouncing up and down). If I stay on the brake and give enough gas to increase the RPM to 1000, the shaking calms down. If I put it into park the shaking calms down. The mechanic says it's my worn engine mounts, but told him it can't be that, since my B21A1 (which also idled low, at 750) didn't shake the car.
3) When stopping quickly, the car sometimes stalls out. And when starting the engine, the car sometimes stalls out (when I release the gas in order to apply the brake to put it into gear).
4) Much less power than my B21A1 -- when going up 6% highway grade, the car maxes out at 75 MPH. The B21A1 had significantly more top end. Even with the reduced displacement, given that Iím still using the fuel injectors, there shouldnít be that much loss in power, right?
5) It doesn't seem to interact with my transmission as well as the B21A1 -- sometimes get delayed shifting.

Any suggestions? The mechanic is willing to work with me to fix the problems at no extra charge (I have a 90-day warranty), but I don't think he knows exactly what the problem is, since I left the car with him for a week and he thought he'd fixed everything, but clearly did not.

Is it an issue that he used a B20A3 instead of a B20A5, since the B20A3 would originally have been carbureted/SOHC/12-valve, while the B21A1 is fuel-injected/DOHC/16-valve?

Given the price I paid, and that I just want to keep the car running for another 2 years (= 6K miles, since I drive only 3K mi/yr), I can live with some issues. But I need to be sure the buzzing isn't an indicator something is going to break, and I can't have a car that stalls out on me.

I had another mechanic take a quick listen, and he said it sounded more like metal-metal contact than knocking. I brought it to my Honda dealer for a full diagnostic, but the mechanic there wasn't willing to touch it, calling it a "frankencar" , so he had no baseline against which to run his tests. The mechanic that did the engine swap said the noise was because there is a chamber in the engine where the oil is used not to reduce friction, but rather to damp vibrations from a moving part within that chamber, but it takes ~100 miles of driving for that to chamber to fill fully, at which point the problem would go away (it hasnít).

Also, one of my cooling fans was broken and, at no extra charge, he swapped in one he had, fixing my overheating problem. However, I now have an odd electrical problem -- the lights on the climate control system that show what you've got selected (vent vs. heat vs. defrost, and recirculate vs. fresh) don't turn off when the car is turned off. Anyone know how much battery drain this causes? Maybe it's little enough I don't have to worry. I can turn off these lights by making sure none of the buttons are fully depressed, but it's inconvenient to do this every time I park the car.
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