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Hey guys,
So i'm in the middle of a engine rebuild and was wondering how far over can i bore out the cylinders. I have a later (8bolt flywheel) b20 engine and I heard that they can take b21 pistons. B21 has a bore of 92 if i'm correct. Has anyone ever taken their b20 this far? Is it pretty reliable?
Tim
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Have your machine shop sonic test the cylinders to ensure you have sufficient wall thickness after the overbore. .100" at the thinnest spots is okay for a street engine.
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It will scare your machinist, but it's done all the time. I've done it a couple of times, and it's a good improvement. You'll need a special head gasket is all. Folks here will know where to get one.
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Hello,
We are building a 2130cc right now for one of our customers.
Pistons are hard to find and so I bought an extra set when I did find them.
In this case, the customer already had the special Elring head gasket for the job.
We prefer this gasket, but I am not sure where to get a new one.
I understand Cometic has or can make a suitable head gasket.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
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I got my last one (still unused) from Mike at IRoll Motors. Unfortunately it is 0.050" thick...
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This is totally of topic, but just disassembled my "F" head, and found that there are 42mm Intakes valves installed. I thought fuel injected heads supposed to have 44mm Intakes? And yes, i'm positive it's an "F" head.
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All injected heads and the last of the carb heads had 44mm intake valves.
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Measure with dial caliper and it comes out to 42mm. Someone must have installed them afterwards...but why???? All intakes are measuring 42mm. All exhaust is measuring 35mm.
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How are you sure it's an F head, BTW?
I've done 2 2130cc B20's so far, no problems at all. Even overbored my old 122's B18 to 2.0L using some B20 pistons, similar situation.
If you have a 6 bolt bottom end, something to consider is having a machine shop press out the wrist pin bushings on the rods, and then doing a very, very light ream for an interference fit on the 24mm B21 wrist pins (press fit, no clips used). I've been running my PV's motor like that for a long time now.
--
'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)
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I used the tech info on the VPD website. It also has plugs in the injector holes. I'm going to remeasure for a third time.
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I remeasure all intake valves and they are all showing up as 42mm. Looks like someone may have installed smaller valves?? Also checked out my cylinder bores and pistons. Pistons have very little wear and there is still some cross hatching in the bores. Looks like someone already bored it to 92mm. Now looks like all I need is a good hone, rings, and head gasket. Just to make sure of what I have, can anyone Identify these numbers I found on the pistons?
Bottom of piston C091: A1: Mahle 92D8
Top of piston 229 07 093
I'm assuming I need to buy standard size piston rings for a B21 motor right?
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If the bore is in such good shape what was the symptom that led you to want to rebuild?
--
Patrick ('68 220, '92 Eurovan, '53 GMC PD4104)
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Rings went bad. Majority of the build is being done on the head though. After inspecting it, there was a TON of carbon buildup that was causing some detonation and pinging. There was also numerous oil leaks, including the rear main seal. My engine bay looked like someone dumped several quarts of oil in there!
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I think they'd have a very hard time fitting smaller valves onto larger vavle seats.
Does it have ahrdened exhaust valve seats? that's a good thing, if you don't have them you might want to consider having some installed while it's all apart.
--
'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)
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I agree with the above. Can I get away with installing hardened seats on only the exhaust? I'm on somewhat of a budget on this build and am trying to stretch the last bit of funds on machine work. Also, i measured my cylinder bores and they come out to just under 92mm. Right around 91.88mm. I measured my pistons and they are showing up as 91mm. I thought b21 pistons were 92mm? They also have a slight dish in them. Could these be different pistons? They say "Mahle 92D8" on the bottom of them. Tried searching but couldn't find anything on those numbers.
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Seat inserts go only on the exhausts -- you're not scrimping by just adding those. However, in the US market at least, 8-bolt B20s already had them fitted.
Pistons are not round, and they are not cylindrical. Measure them at 90 degrees to the wrist pins, and at the same height as the center of the pin. The cylinder bore should be somewhere in the range of .12 to .25mm larger than that dimension.
Standard B21 pistons are 92mm, and only the turbo ones have a dished top. I really don't know what you're dealing with there... In other markets, there's a 2-liter small-bore version known as the B19, but those pistons would be a very large overbore for one of those. And the 42mm intake valves are definitely unusual for a FI head.
Odd.
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Thanks a lot Phil. I was actually waiting for your reply because you seem to know what you are doing with these vintage cars (not saying that anybody else wouldn't have been helpful). I read majority of your articles after picking up my 122.
I wasn't aware that the 8bolt crank engines already came with hardened exhaust seats. Thats great news!!
As far as the pistons go, i'll try and measure them the way you mentioned. I was just measuring them from the top. Rookie mistake on my part, but hey, thats how we learn best. Although, the pistons do have a dished top?!?! I'm just hoping everything works out for me on this rebuild.
Finally, the intake valves. I have no idea why they are 42mm. I would think someone would have a lot of trouble trying to fit smaller valves in it's place. How and why they are in there is beyond me, but I'm certain that they are 42mm. I measured every valve multiple times! O well, at least I know I can always go bigger. Thanks again for everyone's help. It's greatly appreciated!
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"Finally, the intake valves. I have no idea why they are 42mm. I would think someone would have a lot of trouble trying to fit smaller valves in it's place. How and why they are in there is beyond me, but I'm certain that they are 42mm."
I've seen cheated-up ITB race car heads with undersize valves installed, the idea being you get slightly better flow if the valve head is smaller... not the port/seat mind you, just the valve head. It is clearly an illegal modification, but guys are always wanting an edge. I do not know if this actually works, just speculating as to why you have the 42's.
There is an incongruity here though, as anyone wanting to make hp with an IT engine should have been using the "E" head, not the "F".
--
Gary L - 142E ITB race car, 73 1800ES
BlueBrick Racing Website
YouTube Racing Videos
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