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Old 05-20-2014, 08:48 PM   #51
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Gratuitous pic of flaky piston:

It started near an oil control hole, but didn't propagate from it. There's clean metal (even if not much) between the edge of the hole and the cracked off chunk. It doesn't even look like it was moving around much - the way the second ring ran through it kept it pretty much in place and out of trouble. Other than letting some compression sneak on by.

Here are the weird marks on the rods - on the metal underneath the bearings. There are no wear marks on the bearings, but they're only 20K miles old. But the marks here are weird. They're on the thinnest section of the rod, where it tapers down near the head of the rod bolts. I'm not sure if this is an indication of bad things to come/almost happened, or if it's just some sort of machining artifact from when they were made. But it's made me a bit nervous about these rods slinging the B21 pistons around at high rates of speed.

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Old 05-20-2014, 09:06 PM   #52
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What is the size difference between the b18 to b20 rods...?
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Old 05-20-2014, 09:17 PM   #53
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Dimensionally they're exactly the same (vs. the 6 bolt B20 rods, the 8-bolt B20 rods are the same as B21 rods.

But they're lighter, and a bit weaker. The big end 'ring' is much thinner between the stem of the rod and the rod bolts.
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Old 05-21-2014, 12:06 AM   #54
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Dimensionally they're exactly the same (vs. the 6 bolt B20 rods, the 8-bolt B20 rods are the same as B21 rods.
6/8 bolt refers to flywheel mounting flange?

So all of these rods would work on all crankshafts (B18, B20, & B21)?
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Old 05-21-2014, 02:48 AM   #55
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6/8 bolt refers to flywheel mounting flange?

So all of these rods would work on all crankshafts (B18, B20, & B21)?
B20 8 bolt -b21are the same as I am aware of

B18 -b20 6 bolt crank are in their own group I'm guessing?

Gathering info as at the end of summer I'm gonna tear into my 75' b20, interested to see what corners can be cut.
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Old 05-21-2014, 08:29 AM   #56
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Yeah, I worded that awkwardly. The B18 and 6-bolt B20 rods are dimensionally the same, although the B18 rods are lighter and weaker.

They changes the bottom end bearing sizes for the 8-bolt B20's. The 8-bolt B20 rods are dimensionally the same as B21 rods. basically Volvo redesigned the bottom end of the motor a few years before they redesigned the top end for the B21.


I bought a set of B20E rods. I'll have the same thing done with the wrist pins as I had done with the B18 rods - press out the brass bushing, and ream it lightly for an interference fit on the 24mm wristpins.

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Old 05-21-2014, 09:27 AM   #57
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aww. I was hoping you'd dropped in some of john's goodies. on an NA mill that kind of weight savings would be huge
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Old 05-21-2014, 10:05 AM   #58
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I didn't want to spend $$$$ on the old thing.

If I was going to spend $$$$ on it I'd probably put a TDi engine/Toyota pickup trans in it.
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Old 05-21-2014, 01:08 PM   #59
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Gathering info.
Just looking at a B18, I wonder if a Bosch knock sensor could be located at temp-sending unit, or at blow-by pipe on driver's side?

Iirc, years ago, I thought one of the OEMs had placed knock sensor within water jacket, like maybe on 5.7 GM

Have to research thread pitch/size
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Old 05-21-2014, 01:55 PM   #60
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aww. I was hoping you'd dropped in some of john's goodies. on an NA mill that kind of weight savings would be huge
This. A high revving b20 2.1l with 4.5lb knocked off the rotating assembly would be awesome.
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Old 05-21-2014, 05:19 PM   #61
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A high revving.......................would be awesome.
Awesome - 2006 Williams Cosworth CA2006 V8 F1 20,000 rpm
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Old 05-21-2014, 05:40 PM   #62
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Awesome - 2006 Williams Cosworth CA2006 V8 F1 20,000 rpm
Yeah. JohnMC. Swap a Williams/Cossie mill in the pv. **** the Volvo stuff.
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Old 05-21-2014, 09:49 PM   #63
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Yeah, I worded that awkwardly. The B18 and 6-bolt B20 rods are dimensionally the same, although the B18 rods are lighter and weaker.

They changes the bottom end bearing sizes for the 8-bolt B20's. The 8-bolt B20 rods are dimensionally the same as B21 rods. basically Volvo redesigned the bottom end of the motor a few years before they redesigned the top end for the B21.


I bought a set of B20E rods. I'll have the same thing done with the wrist pins as I had done with the B18 rods - press out the brass bushing, and ream it lightly for an interference fit on the 24mm wristpins.
Good move getting the B20 rods. When compared side by side the weak spot in the B18 rod becomes obvious.



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Old 05-21-2014, 10:50 PM   #64
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That pic of them side to side makes me think its a no brained to source out an 8bolt b20 when choosing an engine.
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Old 05-22-2014, 02:47 PM   #65
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Good move getting the B20 rods. When compared side by side the weak spot in the B18 rod becomes obvious.
The weird little marks inside the big ends were *right* on that weak spot.

Either they happened when the big ends were machined, or it's been happening in sue (although the bearings themselves don't have anything odd on them).

But yeah, I think I rolled the dice long enough on the B18 rods, with the heavier B21 pistons and the 7500 revving.

I'd like to make a super light weight rev machine, but there's other things do to right now (second daughter is starting college this fall, first one isn't done yet).
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Old 05-22-2014, 04:05 PM   #66
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Just for the record, this is a GREAT thread for those of us planning B18/20 builds.

Was it ever determined if a B20 8 bolt rod will fit on a 6 bolt crank?
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Old 05-22-2014, 09:07 PM   #67
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No, it won't. The big end on the 8 bolt rod is smaller in diameter and narrower.
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Old 05-23-2014, 09:55 PM   #68
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I bought a set of B20E rods..
Need spares?
Volvo 120 122 Amazon 144 P1800 1800 B20 Pistons + Rods



These are factory bore B20 pistons and rods. Components are in great shape.
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Old 05-25-2014, 05:27 PM   #69
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Are those yours? If so, I guess I bought the set that just arrived in the mail from you as well.

If I need spares, a rod probably broke, and I'll need a whole donor motor.

Actually, I have a set of B20 rods around somewhere in the basement, one of the big ends got scuffed when I spun a rod bearing (no clue why, it was full of Mobil 1 and no issues with the oil system) in the previous motor. I didn't want to reuse the scuffed rod, so I got the B18 rods.

The B20 rods and pistons came in the mail, I'll yank the pistons off and wait for the set of new B21A pistons to show up. Then off to the machine shop to have:
- the pistons balanced
- the wrist pin bushings pressed out and the rods lightly reamed for an interference fit on the 24mm wristpins
- the rods big/small end balanced
- the wristpins installed
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Old 05-25-2014, 05:41 PM   #70
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awesome thread,good stuff.


thx for sharing, ive never seen a piston crack like that

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Old 07-16-2014, 10:19 PM   #71
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My projects always take forever.

The pistons showed up long time ago. Then I took the rods and pistons to the machine shop to be balanced and assembled. They needed a bit of work on the small ends to fit the 24mm wrist pins in.

Then we went on vacation for two weeks right as the machine shop was done. Then I decided to get some new rod bearings - even if the old ones seem perfectly fine, it's still silly to put used bearings back in. So those finally came in the mail. Time to do a little reassembly.

The old cracked B21A piston on a skinny (but light) possibly fragile B18 rod, and the new B21A piston on a sturdier B20 rod.


Does this pic show the way the 22mm rods were worked to fit 24mm wrist pins? No. This picture sucks. I've just wasted valuable interWeb packets posting this pic. Ah well. The bronze bushing is removed, and the steel just needs a *tiny* bit of metal removed. Then they chill the pin, and heat the rod, and it all slides together. As soon as the temps equalize, it's all locked in place. No circlips needed on the pistons. OMG saved .025 grams of reciprocating weightz!


I'd only take two pistons out so far, the busted one, and a 'good' one. I decided to go with 4 new pistons, along with the B20 rods.


Some torque wrenching, some STP used as assembly lube, and a break to go pick and eat blackberries (they're in full gallop right now, about 2 quarts a day, sofa king delish), and all 4 are in.


And.... yeah, I don't have an oil pan gasket. Why don't I order this stuff ahead of time? Dunno. It's part of why my projects take so damn long.
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Old 07-16-2014, 10:28 PM   #72
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Is your crank rotated so all cylinders are at the middle of their stroke, or did you modify your crank to fire all four cylinders at once?
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Old 07-16-2014, 10:33 PM   #73
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It's a new 'flat' crank to go with the planned DEI.
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Old 07-21-2014, 12:57 PM   #74
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Oil pan is on. Head is on. Lifters are... yeah, I had to take the head off and put the lifters on. Wasn't paying enough attention to the order things need to happen on a pushrod block. too much 16V nonsense over the last few years. It's a Cometic HG, it will be fine with a re-installation.

Roller rockers are back on, valve cover is on. And I didn't as much as look at it over the weekend. Went to Cars & Coffee Saturday morning, then we went home and loaded up the backpacks for a short overnight backpack at Hawn State Park.

But it's about ready to go back into the PV again.
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Old 07-26-2014, 07:39 PM   #75
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I sort of felt like using a light new style starter on it, instead of the large, heavy old style. So this morning I went by the PnP and pulled a starter off a '94 940.

Ready to put the motor back in finally.


Taking advantage of slave labor. Pull that lever! Just like manning the oars in Greek times.


Almost high enough. I have to jack the car up in the air too, the legs of the lift are too wide and too tall to fit under the PV's front ent.


About 10 minutes of wiggling, raising, lowering, tilting one way, tilting back, and the motor slips into place. An unflattering pic of my ass working away at those bellhousing bolts:


The new starter is half the size. From 2150 lbs down to 2142!


I'm lazy. This is as far as I got today:


I need to weld on the exhaust header a bit before I put it back on. There was a small gap on #3 where a welding error wasn't sealing properly, it was a bit sooty around the area. I'll weld it and grind it smooth again. The rest of the work will go quickly. Exhaust header, v-band clamp to the exhaust system. DCOE's go on in one large chunk - a throttle push rod pops on, one fuel line, two choke lines. Then the distributor cap and wires/plugs. Crank crank vrooom.

I haven't driven it since last fall, and really, it's been sitting since last spring.
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