Swap - ET2 / A18 / B20A (JDM) / B20A5 / B21A : Head - A20A : Block

[Kabuki]

Well, I've been thinking about this from the 3G Prelude end of things. I have an extra head that came out of an Si, and was looking at what I could do with it. After poking around the shop holding the head gasket up to different blocks and heads, I ran across the B20A/21 Head & A20 block combo. Someone recently posted about attempting it on PreludePower.com, and said there was a conversation here.
First thing, I measured the A20 cam gears, and we will not be able to use two one the head. They are just too big. You can't use the B20 crank gear, because the shaft snout is smaller on the A20. I'm looking in to some others though, and hope to have this worked out soon. I suppose, though, that in the worst case, we'd just have a crank gear made or modified at a machine shop.
The type of engine build will very much depend upon which head is used. The B20A heads are designed for an 81mm bore, so the combustion chamber will actually be smaller, and better for a high compression, Naturally Aspirated build. The B21 head is designed for an 83mm bore, and thus will be a much better match for a turbo application. The B21 is what I plan on using.
As for the timing belt issue, I will be happy to help. But I need an A20 block to mock up and measure. I have access to whatever length of belt I need to try on.

Whoa... All SORTS of misinformation here.
The F and H engines are MUCH larger than the B and A series. The Pistons on the F20/22 engines are 85mm. The Bore on the F23 (98-2002 Accords, 98-99 2.3CL, and 98 Odyssey) is 86mm. The bore on the H23 and H22 are both 87mm. The F and H engines are a good 2 inches longer than the A20/B20, and there is NO way to make it work. The F22B1 and F23A1 are nearly identical. Same VTEC head design, but the F23 has a slightly larger bore, that's all. All of the H and F series heads and blocks have the same piston centering/positions, and the same bolt pattern. The oil galleries are a little larger on the H blocks, but that's pretty much it.
Sorry guys, but this one just can't work. I'm all for the B20A/A20A hybrid though...
Tidbits:
The JDM A18 has an 81mm bore too. Same for the 84-5 Accord engine (sorry, don't remember the US engine code on those).
We at Prelude Power have found that the later model B16 intake manifolds have the same port spacing as the B20A5/B21 units, and don't have the gangster lean to them.
Swap_File: Careful, the junkyard website may be referring to the B20A3 head, which is for the SOHC Dual-Carb unit. Which is a huge pain in the ass, and not worth your time.
Oh, jeez guys... B16s are only good for Civics and CR-Xs... The suck donkey balls in a 3G Accord or Prelude, because of the lack of torque. The B18/20B is better, but... There IS more space in a 3G Accord engine bay than the 3G Lude, and YES there are a few people who are running H22As in their 3G Ludes. It should work okay, and the weght difference changing from an Iron block to an Aluminum block will pretty much negate the additional engine size.

The junkyard's website just lists generic prices for all items, its $38 for any head you can find in their yard. And I did not find one.

Damn... May just have you find a bunch of heads and ship them! Haha... Well, good luck!
Okay, first... What the hell happened? There were three different threads that have apparently been converged in to this one? No I look stupid because I have three different posts in a row, that all refer to different parent posts... Ack...
I'm in Salem, Oregon. I run the front desk at the family Honda and Acura Service and Repair shop, Valley Specialists. I also order and distribute the parts, so if anyone needs anything, let me know. Memebers to any forum I frequent get at least 10% off of Honda list price, usually including shipping. Sometimes substantially lower prices than that.
Now I regret letting the techs toss the A20 engine core we had last year... Oh well... It WAS pretty bad, though.
Yeah... Shipping from minnesota would be a bit high... I may have one I can acquire... It's sitting in an '86 Accord that was brought in and left. The guy hit something, which broke the radiator, so it leaked all of the coolant out, and blew the head gasket on an engine we rebuilt less than a year ago. Dumbass...

[A20A1]

Now there are 12 or so different threads converged here.

I titled the thread differently since all posts basicly cover available head swaps.

If it looks like your post is missing it isn't. I was trying to get all the images on the first two pages along with the posts... but with 12 threads to work with, it was too much. For those that quoted messages in their reposnses or made good replies, the merging of posts didn't do much harm.

[Swap_File]

The 90-91 Preludes with B21 engines are OBD1, but their sensors and distributor do not work well with the Civic/Integra ECUs that are used with Hondata/Uberdata/Chrome.

This is what I found on PreludePower about the distributor/sensor upgrades that are needed to run a B21/B20 with a Civic/Integra OBD1 ECU (which we need to do for the head swap):

I'm using A P75 (LS) computer with Uberdata. The P75 doesn't like the [stock] B21 distributor. For one, the rotors are out of phase between the two distributors. And second, the tdc, cyl, and ckp sensors have different resistances. I measured my B21 sensors at about 1k ohms and the LS sensors at 250 ohms.

When I checked my ignition timing with the P75 and B21 distributor it was way off. It was impossible to set the timing near 15 BTDC. Probably because the rotors are out of phase.

It's been said that the LS distributor won't fit in the B21, but it will. Just installed 95 LS distributor in my B21 yesterday along with LS cams. What you need to do to make it fit is get a distributor end cam cap from a LS and switch it with the stock cap. Haven't been able to tune it yet (Uberdata) but I'll give my impressions after I do. Also removed the stock cyl sensor and replaced it with LS plug.

This should also work with stock B21 cams installed.

http://www.preludepower.com/forums/s...d.php?t=217600

[Kabuki]

The 90-91 Preludes with B21 engines are OBD1, but their sensors and distributor do not work well with the Civic/Integra ECUs that are used with Hondata/Uberdata/Chrome.

This is what I found on PreludePower about the distributor/sensor upgrades that are needed to run a B21/B20 with a Civic/Integra OBD1 ECU (which we need to do for the head swap)

You shouldn't NEED to go OBD1 for this. You should be able to use the OBD0 ECUs from the Civics and Integras and not have to rewire as much stuff. The stock 3G Accord Distributors would all FIT, though bolting them in might be an issue.

[racerx]

OBD1 and OBD0 ECU's in the 3rd gen prelude's have different pinouts. No idea why, but Honda likes to be special sometimes.

The B21 Preludes from 90 and 91 are the only OBD1 Honda's with injector resistor boxes. (that I know of)

Anyway, here's the run down:
If you want to use a B21A1 block/head/sensor combo, you'll need the OBD1 ECU and wiring harness.
I tried using an OBD1 civic ECU in my OBD1 prelude, didn't work right. It ran, but it ran weird; very lean. You'll need to chip the civic/teg ECU with uberdata to make it work right.

There IS an alternative, however.
The B20 head will bolt up to the A20 block as well, and those sensors and wires and OBD0, so there's a much better possibility that the A20 ECU would be able to manage it, or the B20 ECU might actually fit the wiring harness.

For everyone's information, swapping the B20 head on the B21 block increases compression and power by a little, so it should have the same effect on the Accord now that I think about it.

Next time there's a B20 OBD0 prelude in the junkyard here, I'll pull the ECU and see if it will run/fit in the 3G accord.

[carotman]

Everything that relates to the wiring has been discussed in the engine swaps section when I made my PK2 How-to. It's also explained how to run a B20A with a PJ0 ECU (which shouldn't be done).

All you need to do is choose the ECU you want and install the distributor that will match that ECU. There is no such thing as an OBD-0 or OBD-1 head. Heads are heads, sensors are sensors and ECUs are ECUs. Every 88+ Honda engines use basicaly the same sensor between obd-0 and obd-1.

The BEST ecu to use without any doubt with the A20A/B20A hybrid is the P06. It's cheap, reliable and chippable by every tuning software around. Then, you install a B18B cam endcap to be able to use a B18B distributor and you plug the exhaust cam with the B18A/B endcap (for a better underhood look). You make an OBD-1 conversion harness and install a 4-wire O2 sensor.

If you're worried about emission controls, the P14 ECU is the thing to use but will make it run richer and doesn't allow you to use a Uberdata. It's only good because it will retain the EGR setup. Any OBD-1 Accord ECU would fit but you just need to choose the one you want. Remember, this is ONLY to keep the EGR functionnal.

A Stock P06 or P75 ECU doesn't work well on a B20A because of the fuel and timing curve. The B20A has a long stroke and needs higher timing to work fine. It's a 2L and will also need a little more fuel. This is why you need to chip it.

The B21A head gives less compression than the B20A because it has a bigger combustion chamber (bigger bore)
Anything that needs to be cleared out?

[A20A1]

So carotman, did you ever see that b20/a18 car again?

[carotman]

Nope, the dork junked it

It's one of those guys that will drop lots of money in a car and just cut corners. He had a coolant leak on one of the main hoses. The engine overheated.... and blew.

It was an ET2 with a B20A3 head I beleive.

[Kabuki]

The 4G and 5G OBD1 Accords and 4G Preludes use resistor boxes as well.

[Swap_File]

I got a crankshaft timing gear from the junkyard today (Still no head):



Prelude B20A/B21 gear on left, A20 gear on right. A20 crank in the middle (the junk crank I have from the engine that spun a bearing).

Prelude B20A/B21 Shaft: 28mm
Accord A20 Shaft: 25mm

I will take this into the local machine shop sometime this month and see what they can do for a shim.

Also, I think this post got lost when the threads combined:

Mustardcat from preludepower tried to put the A20 cam gears on the Prelude B20A/B21 head:

Sorry the a20/a18 gear is just a hair too large, they will touch eachother. It does slip onto the b20 cam though.

After thinking about it a bit, I think you will be better off going with all the b20a/b21 gears. Since you will be able to pick up any b-series adj. cam gears, not to mention you may not be able to find a timing belt long enough to work with 2 a20 gears on there.

[A20A1]

A smaller diameter B20A/B21 gear would be less rotational weight since the radius isn't as large... a big bonus aside from having the adjustable ones available.

The A20 gears would give more mechanical advantage to turn the camshaft against the rockers/valve springs... maybe if you had heavier springs that could came in handy perhaps?

[Kabuki]

I was thinking... I need to check the size of the gears on my '89 Prelude B20A3 SOHC, Dual Carb. It's essentially the same design as the head from the dual carb 2G Ludes, but uses the B20A bottom end.

[racerx]

that's definately worth looking into! could solve the problem right there!

[Swap_File]

A smaller diameter B20A/B21 gear would be less rotational weight since the radius isn't as large... a big bonus aside from having the adjustable ones available.

I just put them on my scale, the B20A gear (without shim) is 6.7 oz and the A20 gear is 11.4 oz.

[A20A1]

I was thinking cam gears not the crank. but thats just as good.

[Swap_File]

I did some investigation in search of a 25mm crankshaft timing gear.

I limited my search to Hondas and Accuras that had adjustable cam gears available from AEM. (their site was easily searchable )

These are the different "Families" of camshaft cam gears (According to AEM):

AEM PN 23-800
38 Teeth
Camshaft Gear Fits - Yes (from Kabuki on PreludePower)
Crankshaft Gear Fits - ?

-Might be the same as the 23-804
-Most companies sell the same gear for 23-800 and 23-804 applications

Found in:
Honda Civic 1988-95 D15/D16 SOHC 	
Honda del Sol 1993-95 D15/D16 SOHC
Honda CRX 1988-91 D15/D16 SOHC

AEM PN 23-801
42 Teeth
Camshaft Gear Fits - Too big for DOHC, gears will touch.  Unsure of shaft size.
Crankshaft Gear Fits - Doesn't matter, the camshaft gear would be too big.

-Could possibly used for adjustable cam gear for the A20?
-See picture below of H22 belt with A20 gear

Found in:
Honda Prelude 1992-02 H22 DOHC

AEM PN 23-802
34 Teeth
Camshaft Gear Fits - Yes
Crankshaft Gear Fits - ?

Found in:
Acura Integra 1990-01 B17/B18 DOHC
Honda Prelude 1992-96 H23 DOHC
Honda Prelude 1988-91 B20/B21 DOHC 	(28mm Crankshaft)
Honda del Sol 1994-97 B16 DOHC
Honda Civic Si 1999-00 B16 DOHC
Honda CRV 1997-01 B20 DOHC

AEM PN 23-803
40 Teeth
Camshaft Gear Fits - ?
Crankshaft Gear Fits - ?

Found in:
Acura Integra 1986-89 D16A1 DOHC  	
Honda Prelude 1992-96 F22 SOHC
Acura CL 1997-98 F22/F23 SOHC
Honda Accord 1990-02 F22/F23 SOHC 	(F22 30mm Crankshaft)
Honda CRX 1985-87 EW3/EW4/D15 SOHC
Honda Civic 1985-87 EW3/EW4/D15 SOHC
Honda Odyssey 1995-98 4 Cyl.

AEM PN 23-804
38 Teeth
Camshaft Gear Fits - ?
Crankshaft Gear Fits - ?

-Might be the same as the 23-800
-Most companies sell the same gear for 23-804 and 23-800 applications.

Found in:
Honda del Sol 1996-97 D16 SOHC
Honda Civic 1996-00 D16 SOHC

AEM PN 23-805
38 Teeth
Camshaft Gear Fits - No
Crankshaft Gear Fits - ?

-If the Crankshaft gear would fit, it could maybe be used with 23-800

Found in:
Honda Civic 2001-03 D17 SOHC

I would assume that the difference between each family is the number of teeth on the gears, or possibly the camshaft diameter.

According to Honda-Tech H22 and F23 crankshaft timing pulleys use the same shaft size.

I do not know if the crankshaft timing gear pully diameter has anything to do with the family the camshaft gear comes from or not.

If anyone wants to try to use pulleys from other families than "23-802", be sure that the camshaft pulleys will fit, as well as the crankshaft.

Feel free to post any of the measurements you can find, I will edit the list as I find more information.

[racerx]

that is outstanding information!!! way to go!

[Kabuki]

Okay, sorta bad news... The B20A3 (SOHC) uses a 40 tooth gear. So not really any help there. The two possibilities I see as the best possibilities are these: All three gears from the 1G Integra's D16A. I seem to remember that the crank gear from the D16Z6 was slightly larger than the shaft on the D16A crank that I bought to repair said D16Z6. If we need to, bore out the crank gear, but I'll bet either the crank gear from the D16A or D16Z6 will work for our application. Or we machine a sleeve/bushing for the B20A5/B21 crank gear. I'll look at my other D16Z6 sometime today.

[smufguy]

From what i know you can use two Adjustable cam gears from the SOHC F22 (4g accords USDM) and use it on your B20A. Thats what Carotman (Jean) did.

[Swap_File]

From what i know you can use two Adjustable cam gears from the SOHC F22 (4g accords USDM) and use it on your B20A. Thats what Carotman (Jean) did.

While the F22 camshaft timing belt pulleys would probably fit, the ratio would be incorrect with the stock A20 crankshaft timing belt pulley.

If the Accord B20A had the same size crankshaft pulley as the A20 it could be swapped over, but according to this https://www.3geez.com/showpost.php?p=59367&postcount=10 it does not. The Accord B20A has the same size diameter shaft as the Prelude B20/B21 ( 28mm ) which means it will not fit on the A20 crank.

Okay, sorta bad news... The B20A3 (SOHC) uses a 40 tooth gear...

They could (maybe) still work if the crankshaft pulley fits. We know that 40 tooth camshaft gears are on the Accord B20 (https://www.3geez.com/attachment.php?...6&d=1032502584) 40 tooth gears might also fit the Prelude B20/B21. I will measure the distance between the B20's camshafts the next time I am the junkyard.

The only other possible problem with using a 40 tooth gear would be finding a timing belt of the correct length.

[Swap_File]

I asked around about the different ways to fill the 3 extra holes in the Prelude B21A1 block. Here are the suggestions I recieved:

Weld the holes shut - Would definately work. Would require head shaving. Most expensive option. Cannot be done yourself. Could warp the head if done improperly.

JB Weld - JB weld is rated to 500 degrees, which could be a problem. I would probably not trust it.

Liquid Aluminum Block Filler - Very strong, but can be tricky to use and apply properly. Head would have to be stripped down and cooked in an oven for proper curing.

Liquid Gasket - Can only be used when filling a hole that will be up against the block. Not a permanent solution. Not something that can be safely used for this head swap.

Thread the holes and install plugs - Just tap the holes and install some hex socket plugs (http://www.midwestsocket.com/HexKeys.jpg). Possibly use loctite red, and turn them in so they are deeper than flush. It was suggested that brass plugs would work the best. I do not know if loctite would be useful because it apparently starts to lose effectiveness at 500 F.

Most people I talked to seemed to think threading the holes for plugs would be the best solution. At this point I would agree.

[phrenology]

Does anybody have a B20A3 (SOHC) crankgear for sale or do you know if it will fit the A20A crankshaft with little or no modification?

[smufguy]

swap file. The first quote that you have of me is strictly for a B20A motor, not a hybrid one.

the second quote is not mine by the way. The tooth count is somehting i am unaware of.

[Swap_File]

swap file. The first quote that you have of me is strictly for a B20A motor, not a hybrid one.

Yeah, I was just was hoping it would work for the hybrid also, but it turned out not to.

the second quote is not mine by the way. The tooth count is somehting i am unaware of.

Sorry about that, I had copied and pasted the quotes tags and while editing the post and forgot to change it to Kabuki. I fixed it now.

[Kabuki]

Okay, I've got a 3G LX-i in for a head gasket, and the head is still at the machine shop till tomorrow. So tonight, after everyone else leaves, I'll go stick the B20A5 head on the block and try some timing belts. Now, since the A20 uses a 108 tooth belt, and the B20A5 uses a 124, I'm guessing that the belt will need to be somewhere in between. Something like the 112 or 113 tooth belts from the F series (VTEC and non-VTEC engines, respectively) should be pretty close. The F engines, of course, use the belt to drive the water pump, but are single cam. The PK1 belt from the SOHC B20A3 might work too, but it will all depend upon the gears we use.