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Discussion Starter · #1 · (Edited)
measuring my exhaust cam last night and not sure of tolerances. Specs put lobe height at 1.3359" with a max runout of .0023" So if I understand this correctly the min lobe height is 1.3336"

This is an exhaust cam from a JDM B20a. When measuring I was actually getting measurments greater then 1.3359

Here are measurments
1.3336
1.3345
1.3364
1.337
1.337
1.3374
1.3374
1.3369

Are the JDM cams different???

I am looking for a good B21a1 exhaust cam if anyone has one collecting dust.
 

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toguetastic
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steve! i'm sure he'll be all over this. there are only like 2 or 3 people who have mic'd cams for our cars and he's got the most measurements i've seen. actually you could probably find the numbers you're after in his thread, which is linked in his sig. just find somewhere where motoxxxman has posted and look at the cam link in his sig.
 

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I once had a jdm b20a and it had way different cams than the b20a5. My buddy came over to swap out to the b20a5 cams, but once he found the the lobe lift was shorter on the jdm b20a's he felt better about the staying with his b20a5's cams. The b20a engine was stamped 88, so it must have been one of the first b20a's, I just guesses that the 88's had a shorter cam lobe lift. I left it at that, what do you think moto?
 

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Discussion Starter · #4 ·
looked at his post several times and nothing on a jdm cam specs. The other thing is it appears that he is measuring lift with cam in head while I measured the lobe height with cam out. Also, unless I missed it, he does not mention runout specs.
 

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He has no numbers on the b20a cams because they are pretty close to the b20a5 cams, according to his write-up. He did graph the differences though. He only states that the b20a5 exhaust cam is slightly better than the b20a.

Quote:
b20a cams:

today i was able to get all the usual data on a set of jdm b20a cams, thanks to secluded luder for providing them for testing. i was shocked when i looked over the results, and especially shocked when i graphed them. well, kind of a mix between seeing what i expected for one, and something totally unexpected for the other. due to the graphic nature of this program viewer discretion is advised lmao! actually, due to the results of the data collected, im not going to bother posting the actual info on them as i have for the above other cams. to sum it up, the jdm b20a intake cam is 100% identical to the USDM b20a5 intake cam. the jdm b20a exhaust cam is similar to the b20a5 exhaust cam, but a bit worse. to further explain and see the similarities, simply lok at the following graphs; they show all:
sorry to disappoint you guys lol
 

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Discussion Starter · #6 ·
back to my original question - when is the cam out of spec "worn out"

I am not too concerned about my exhaust since I am going to use a b21 exhaust. What I am trying to find out is

1. is the jdm specs same as us - appears to be "yes"
2. what is the limit for "out of spec"? - .0023" off the lobe height?

lobe height for intake is 1.3274"

I just thought it was odd that on the jdm I was getting lobe height greater then the listed spec for the B20a5 exhaust.
 

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Sorry, that's all I can think of if you are seeing that much of a difference. maybe the cams that moto measured were not really JDM b20a cams?
 

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In motoxxxman's thread on the black 3rd gen (for his GF?) he used a JDM intake cam. He speced the B20a intake cam out to be the same as, or almost the same as a B18b intake cam. This struck him as an odd find considering he has speced other B20a intake cams to be inferior to the B20a5 and B18b intake cams.

I think that's the tail but moto himself could tell it better. I hope this post is accurate enough to expand the possibility that the B20a may have used two different intake cam specs.
 

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ok im here lol
my first thought was "wow, i'm actually quite shocked you have so much variance between the 8 cam lobes. more than 0.004" variance. honda cams are usually within 0.002" even used. brand new, they're always within 0.001" of each other.

honestly, my guess is that you either have a fairly worn cam, or you didnt exactly measure it properly. cam lobes are fairly difficult to measure accurately due to their shape, and that it has to be measured as total width of cam and lobe, then subtract the base circle width. if either measurement is off, it'll throw off the calculated lobe height.
it's very possible that the engine you got that cam from wasnt maintained properly in keeping the valve lash accurate at all times. if the lash was too tight on any of the valves, it'll cause constant contact between rocker and cam, and will obviously cause some wear, faster than the ones where the lash is correct or too loose.

for the record though, jdm b20a cams vary from year to year just like i've found the b20a5 cams to vary from year to year. and in most cases, the jdm intake cam is the same as the usdm intake cam, but the jdm exhaust cam is usually a hair smaller than the usdm exhaust cam. at least from what i've measured so far.
 

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Discussion Starter · #12 · (Edited)
ok im here lol
my first thought was "wow, i'm actually quite shocked you have so much variance between the 8 cam lobes. more than 0.004" variance. honda cams are usually within 0.002" even used. brand new, they're always within 0.001" of each other.

honestly, my guess is that you either have a fairly worn cam, or you didnt exactly measure it properly. cam lobes are fairly difficult to measure accurately due to their shape, and that it has to be measured as total width of cam and lobe, then subtract the base circle width. if either measurement is off, it'll throw off the calculated lobe height.
it's very possible that the engine you got that cam from wasnt maintained properly in keeping the valve lash accurate at all times. if the lash was too tight on any of the valves, it'll cause constant contact between rocker and cam, and will obviously cause some wear, faster than the ones where the lash is correct or too loose.

for the record though, jdm b20a cams vary from year to year just like i've found the b20a5 cams to vary from year to year. and in most cases, the jdm intake cam is the same as the usdm intake cam, but the jdm exhaust cam is usually a hair smaller than the usdm exhaust cam. at least from what i've measured so far.
This is a used cam. Do not know any history and that is why I am checking before reinstalling into motor.

As far as not getting good measurments, I will agree that the way that I measured them (with a micrometer out of the block) can be tricky but the the 2 that are way off I measured several times so I know they are real close to being right. Since I am not going to use the exhaust - no big deal but I sure do not want to put the intake back in if it not within spec.

I will measure the intake tonight and post tomorrow.

If I can find a way to mount my gauge I will measure the lobe lift in the head. Will give us a more accurate reading and condition of cams.
 

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Discussion Starter · #14 ·
ok, some of my measurments were off. I put the cams back in the head and used a dial indicator with a magnetic base to measure lobe lift. All of my measurments were within .001" fo each other but...

Max lob lift on intake - .034"
Max lobe lift on exhaust - .023"

b20a5 cams:
intake cam:
open point: (@ the following lift at the valve)
0.010" 5.5 degrees BTDC
0.020" 8 degrees ATDC
0.030" 13 degrees ATDC
0.040" 16 degrees ATDC
0.050" 19 degrees ATDC

close point: (@ following lift at the valve)
0.010" 241 degrees ATDC
0.020" 222 degrees ATDC
0.030" 217 degrees ATDC
0.040" 213 degrees ATDC
0.050" 210 degrees ATDC

duration (@ following lift at the valve)
0.010" 246.5 degrees
0.020" 214 degrees
0.030" 204 degrees
0.040" 197 degrees
0.050" 191 degrees

max lift:
0.356" @ 118 degrees ATDC
0.209" lobe lift

lobe center:
114.5 degrees ATDC

valve lift @TDC:
0.0135"

exhaust cam:
open point: (@ following lift at the valve)
0.010" 244 degrees BTDC
0.020" 225 degrees BTDC
0.030" 219 degrees BTDC
0.040" 215 degrees BTDC
0.050" 212 degrees BTDC

close point: (@ following lift at the valve)
0.010" 37 degrees ATDC
0.020" 0 degrees, perfect TDC
0.030" 6.5 degrees BTDC
0.040" 10 degrees BTDC
0.050" 13.5 degrees BTDC

duration (@ following lift at the valve)
0.010" 281 degrees
0.020" 225 degrees
0.030" 212.5 degrees
0.040" 205 degrees
0.050" 198.5 degrees

max lift:
0.366" @110 degrees BTDC
0.215" lobe lift

lobe center:
113 degrees BTDC

valve lift @TDC:
0.020"

So now I think I am more confused. These lifts are way off the B20a5 cams posted by MOTOXXMAN. Possibly possibly doing something wrong. Will try and take some pics over weekend to show how I am getting the max lobe lift.

Looking at my cylinder walls I found some rust so all this might be a mute point since it looks like I am going to bore out to 83.5 and get different pistons and cams. "if I gotta do the work, I might as well go big"
 
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