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

[baby D]

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.

okay guys check this out the only problems you are gonna have is the belt, but i cant find a b 21 head, any way you need to use 2- a20a cam gears the cam and crank will be times perfict, how ever, i cant tell you about the water pump, belt routing, or how to get the tentioner to work, please pm me when you know, and tell me what f@#$ing car to get the head off of please its p*%$ing me off!!, but it should be a bolt in.

[A20A1]

I thought they said the A20 cam gear was too large and would hit eachother.

[Swap_File]

They are too big, confirmed by members of preludepower.

I still haven't found a B21 head, so I have not done any more work on the head swap project yet.

[Kabuki]

Sorry guys, the B21A1 was ONLY available in the USDM 90-1 Prelude Si (not 2.0Si). There was a B21A available in the JDM 3G Prelude SiStates (extremely rare), which was neat because it came with iron sleeves (happy!) instead of FRM (difficult to work with). I had planned on using my B20A5 head on my B21A1 engine, to up the compression, and then use the B21A1 head on an A20 block, so I can turbo that bitch. But if you want a naturally aspirated engine, just get the B20A5 head from ANY of the 88-91 Prelude 2.0Si engines. The compression will be a little higher too...

[Swap_File]

I crunched some numbers, I think a B20A5 head on a A20 block with the fuel injected pistons should give about 9.6:1 compression.

The local junkyard finally got a second 3rd generation prelude in, it has a B20A5 in it but I am going in on friday to grab the head anyway. I scouted it out and started on removing it earlier today. I figure I can test fit it to my junk engine and see what happens.

[smufguy]

keep me updated on that swap_file.

[Swap_File]

I picked up a complete B20A5 head yesterday at the junkyard. I went to test fit it today, when I noticed that one of the head bolts do NOT line up. Check out these pictures:





The intake side (upper in the picture) middle head bolt on the A20A3 is offset. All the head bolts on the B20A5 and B21A1 head are in straight rows.

I do not recall this problem ever being mentioned before in this thread.

Everything else does seem to line up fine.

Any ideas?

[racerx]

uhm... i put all the head bolts through my B21A1 head into the A20A1 block once... no problems.

[smufguy]

the best way to show the difference is to compare the head gaskets. The head is not realy making much sense to me, its soo much dirt there, im getting distracted.

[Swap_File]

Here are some more pictures:

B20A5 Exhaust Side Bolts


B20A5 Intake Side Bolts


A20 Exhaust Side Bolts


A20 Intake Side Bolts

(Note how the straight edge does not touch the farthest two bolts at all)

Here is one of gofast's pictures with the problem area circled:

(B21A1 head with A20 gasket)

[Swap_File]

I went out to the shop and looked at it again. I can put all the other bolts in, and then look down the remaining hole, and I can see the offset in the block for the bolt hole. I measured the offset to be between 2mm and 3mm.

The only way I can think of to deal with this would be to drill the one hole in the head larger (an extra 2-3mm all the way around), and use a modified washer on top. Hopefully this would not cause any problems with weakening the head.

It will be a while before I try anything; maybe there will be an alternative by then.

While I was at the junkyard I also measured the B20A5/B21A1 intake manifold. As long as we do not use the B20A5/B21A1 intake (and stick with the A20 or B18, etc intake), I do not think hood clearance will be a problem.

[smufguy]

THAT is a problem.

What i think is that we enlarge the existing head stud hole far enough to have the head stud to go all the way in to the block. then use the hole surface area and the head deck height and use a block of aluminun machined to the same area as an insert. engineers and anyone who uses CAD might understand this better. So basically u machine a piece of aluminum (6061) and then drill the proper whole into it for the head stud to go thru. That would be the better way of filling up the hole.

Any leeway in the headstud hole will distort and lift the head and cause it to leak or blow a head gasket. Filling up the hole with some kind of industrial filler (the ones that can patch a damn broken axle) also sounds tempting, but the reliability of it is a little sketchy. If that hole is the only thing thats gonna stop us from swapping the head onto this block, then it needs to be tackled in different ways by people with different experiences. I for one wlll defenitely undertake this and look into it more closely.

[racerx]

I'd bet that any machine shop could move that hole. they'll probably just drill it down and fill in the other side, no problem. you should call a local place and see what they think.

[Swap_File]

This problem bolt hole is special, because the oil from the block comes up around this bolt to feed the head. We really can't block it off unless we re-route the oil. We might be able to hook up at either end of the block (See picture below).

If I drop the head bolts into the head I can wiggle them all side to side. The holes are all atleast a millimeter or two larger than the bolts already. If the hole was drilled bigger, all the pressure would be spread out over a smaller area, so either the bolt could try to pull through the washer, or the head could try to deform (or both). I just do not know if the block or the washer could end up being a weak point.

Here is a picture of where the oil goes in the head:


Red is where the oil comes up around the bolt from the block, blue is for the long holes bored through the head for oil, purple is for the plugs screwed into the head, and green is for the things that squirt out the oil onto the cams.

I am going to look at the head again tomorrow, and double check that everything else lines up.

[Ichiban]

Anything new on this? maybe if you use a thick and wide washer on the head stud it would distribute the pressure evenly over the original "pad" for in the head it would clamp reasonably well

[Ichiban]

THAT is a problem.
What i think is that we enlarge the existing head stud hole far enough to have the head stud to go all the way in to the block. then use the hole surface area and the head deck height and use a block of aluminun machined to the same area as an insert. engineers and anyone who uses CAD might understand this better. So basically u machine a piece of aluminum (6061) and then drill the proper whole into it for the head stud to go thru. That would be the better way of filling up the hole.
Any leeway in the headstud hole will distort and lift the head and cause it to leak or blow a head gasket. Filling up the hole with some kind of industrial filler (the ones that can patch a damn broken axle) also sounds tempting, but the reliability of it is a little sketchy. If that hole is the only thing thats gonna stop us from swapping the head onto this block, then it needs to be tackled in different ways by people with different experiences. I for one wlll defenitely undertake this and look into it more closely.

I don't believe the extra leeway in one or two of the bolt holes will cause distortion as the head is located side to side by the dowell pins, and remember the clamping force is down agains the deck of the block. the stock holes and bolts already have some clearance, especially this hole that flows oil past the bolt (right or am i mistaken here?). I say drill out the hole and use (or make) a thick washer/spacer/cap to distribute the force and keep the oil in. the only problem i could see is maybe interference with valve train parts as the washer/spacer/nut combo would take up slightly more space than it originally did.

[smufguy]

after talking to some peopl i know who work on cars and engine builders, its what i thought before. The washer or spacer or anything wont help. alon with the hole being enlarged, it also needs to be filled and the stud needs to have the same clearance as the stock hole. obviously people are going to rebuild their motor/head when a project like this is undertaken and ARP studs will be used and they dont flex a bit. As long as there is no space for it to put side load on the head stud (in our case, a head bolt).

[thegreatdane]

From what I recall the ET engines have an offset oil jet compared to the A20 engines. But I dont recall if the head bolt was offset too... I had a picture showing the difference but unfortunately deleted it the other day..

[Ichiban]

so what you are saying is that the far side of the hole has to be brought closer to the stud even though it's still not making contact with anything? why? It's not that i don't believe it, i just can't see it making any difference, really. The head is gonna clamp just the same with that gap filled or not.

[Ichiban]

so...the prelude B-series heads need a hole moved to fit on the A-block...so why not machine the bastard out and try it? or is the head of the bolt gonna hit the camshaft? That's probably why the factory moved that hole. Also, does the A20 block provide oil to that hole? I'm all for the project, but some questions need to be answered, and solutions found. Who doesn't want a 4 valve DOHC A20?

[gfrg88]

ok so if it were possible too do something about the hole, what would you do about the cam gears and the belts????

[Ichiban]

if i absolutly had to, i'd machine a crank pully to match the cam gears of the head. however, i'm sure there are stock parts somewhere that will work. i have a buddy who works at a bearing and transmission place, if i can get the required specs of that gear i'll contact him and find out. in terms of belts, i suggest trial and error. I'm seriously contemplating attempting this, and i'm not usually one to let crap details stand in the way.

Can we in fact use the A20A3 intake manifold on the B20A3/A5/B21 heads?

[Ichiban]

Swapfile, if you can mike out the b20 crank gear and give me all the dimensions (width, tooth height/spacing/count) and the ID of the A20 crank gear, it would go a long way to trying to order something specific. like i said, i'll have my buddy check a massive database of industrial power transmission supplies, there has to be something...

any word on the A20A3 intake on the B20A5 head?

[A20A1]

Can we fill in the bolt holes and have them redrilled along with redrilling the oil passages horizontaly to clean out any debris.

That Alumaloy may come in handy.

THAT is a problem.

What i think is that we enlarge the existing head stud hole far enough to have the head stud to go all the way in to the block. then use the hole surface area and the head deck height and use a block of aluminun machined to the same area as an insert. engineers and anyone who uses CAD might understand this better. So basically u machine a piece of aluminum (6061) and then drill the proper whole into it for the head stud to go thru. That would be the better way of filling up the hole.

so you mean make an aluminum cylinder and drill a hole in the cylinder to one side to accomodate the offset in the bolt spacing.

Or what about a half/half.

Drill the holes, add the insert but fill in some area that are close enough to the top and bottom of the hole to be heated by a torced and then fill it in with alumaloy.

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.

missed this post, sorry.

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[Legend_master]

having the hole filled and then re drilled would be the rout I would take. For my LS/Vtec I had this done. The filled the old oil passage hole on the head and redrilled a new one. YOu could have the passage on the block moved, but it is much more difficult to have this done. As for price, I paid $90.00 to have it done and they did a damn good job with it.