shaved head

[stephensimmons]

I got a quick question for someone. If you shave your head to build up compession i know it lowers your head to the block which would offset your timing a litte. Now dose it advance or retard your timming when you do that?

[cubert]

It will retard it, if i remember correctly.

[cygnus x-1]

Yep, it will retard the cam and therefore the ignition timing. You can rotate the distributor to correct the ignition timing but you need an adjustable cam pulley if you want to correct the cam timing. The change is not huge though, roughly 2 crank degrees per 1mm you take off the head.

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[stephensimmons]

Ok thanks for the imfo!

[stephensimmons]

Whats the most you can shave off a head without messing it up?

[cygnus x-1]

Whats the most you can shave off a head without messing it up?


Depends on who you ask. If you go by the indicator dots on the under side of the head it's about 0.050". I've heard of people doing up to 0.060" though without issue. I'm planning to try 0.080" on the head I'm currently building. I haven't done it yet but I did try a test cut at 0.080" on a chopped up head that I'm using for R&D. Here's a picture of it:


http://bluegreenlabs.com/Prelude/Mods/HeadPorting/ChambersMilled2mm1.JPG




If you do this you will want an adjustable cam gear to get the cam timing back to where it's supposed to be. It would also be wise to check the piston to valve clearance, but from what I can tell it will still be ok. The only other possible issue is that the oil jet may stick up too far into the pocket in the head. This is an unknown still but if it is a problem, either the oil jet will have to be cut down or the pocket in the head will have to be made deeper.


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[Tomisimo]

yes to everything cygnus said, but a small correction, for each MM you shave you have timing retarded by 3°, there fore you have to have adj.cam gear.

[stephensimmons]

Ok thanks alot for the imfo guyz!

[cygnus x-1]

yes to everything cygnus said, but a small correction, for each MM you shave you have timing retarded by 3°, there fore you have to have adj.cam gear.


How do you get 3 degrees? Diameter of the cam pulley is 125mm, circumference is 125 * pi = 392.7. To take up an extra 1mm the cam pulley will rotate 1mm of it's circumference, so 1 / 392.7 = 0.0025465 of a full 360 degree turn. 0.002565 * 360 = 0.9167 degrees. That's in cam degrees though so multiply by two to get crank degrees. 0.9167 * 2 = 1.833 degrees.


Regardless, the timing will change. If you only take 1mm off then you could probably live with it. More than that and the low end torque will start to suffer due to the retarded cam. High RPM torque would improve though.


I was going to mention before, the casting looks plenty thick enough to take off 2mm (0.080"). Slightly more might be possible but the risk of clearance problems and head warping increases. 2mm off would get you to 11:1 CR with stock pistons, maybe a little less with the valve job and some deshrouding work in the chambers. 11:1 and higher you will likely not be able to run pump gas without pulling way back on the timing. Cam selection will be more important too. With high static CR you need more overlap in the cam to lower the dynamic CR at low RPM so that it doesn't tend to detonate.


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[Tomisimo]

Ahh, my bad. Maybe it was for B16/18 DOCH engines.. was reading a article on that same matter. Was considering to shave mine B20.

[stephensimmons]

Well i just picked up a a20a3 and 5 speed tranny today and bout to start tearing it apart so i can start my build! Anyone can tell me how to post pics? Im bout to search to see if i can figure it out.

[dacantu]

1 take the picture
2 upload the pictures in photobucket.com
3 when you see a picture you want to upload, click it (in photobucket still)
4 the picture will maximize and there will be some codes in the bottom left of the screen
5 click the one that says direct link (it will say *COPIED)
6 (back in 3geez.com) when you go to write a message paste it into the message and voila.

[Tomisimo]

yes.. or use image link location and post it true this image http://www.3geez.com/forum/images/editor/insertimage.gif you have on your reply screen

[stephensimmons]

Thanks alot!

[stephensimmons]

Well im getting started today on my 10.50 a20a3! Hopefully I'll have it done buy the east coast meet in N.C. http://i754.photobucket.com/albums/xx186/stephensimmons/89a-2.jpg

[stephensimmons]

How do you get the pics to come out larger?!:banghead::rant:

[stephensimmons]

yes to everything cygnus said, but a small correction, for each MM you shave you have timing retarded by 3°, there fore you have to have adj.cam gear.

I dont know if anyone knows it or not but but I just got word that we (the a20's) should have an adjustible came gear just for US in about 3 weeks!:flash::beer:

[2oodoor]

How do you get the pics to come out larger?!:banghead::rant:

photobucket changed something since I used it, I discovered this week that if you click on SHARE there will be several formats there to choose from for sharing.. look for IMG (full size) ..highlite it and copy paste. to the insert image block (delete the http because your copy will have that already, then paste it.

k where in sc are you? close to columbia?

[import racer]

How does shaving the head change the timing?

[MessyHonda]

How does shaving the head change the timing?
when you shave the head the cam will not spin the same as the crank anymore because there is less material...it does not change it al whole lot but enough to throw it off factory specs

[cygnus x-1]

when you shave the head the cam will not spin the same as the crank anymore because there is less material...it does not change it al whole lot but enough to throw it off factory specs


Yeah, It's kinda hard to explain without pictures, but the cam and crank have to be synchronized with each other. That is they both need to be at TDC at the same time. Because they are connected to each other with a toothed belt, the distance between the cam and the crank becomes critically important for them to stay synchronized. When you mill the head, it changes the distance between the cam and the crank. It's not much, but it's enough to create a little bit of an offset between when they each cross TDC. The cam will lag behind the crank by an amount directly related to how much the head is milled. If it was possible to mill enough off, you could just reset the cam pulley by one tooth and everything would line up again.


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[stephensimmons]

photobucket changed something since I used it, I discovered this week that if you click on SHARE there will be several formats there to choose from for sharing.. look for IMG (full size) ..highlite it and copy paste. to the insert image block (delete the http because your copy will have that already, then paste it.

k where in sc are you? close to columbia?

Im bout an hour south of columbia im near charleston.

[2oodoor]

How does shaving the head change the timing?

It puts the head closer to the block (pulleys closer) so that in turn makes the original marks on the cam gear slightey inaccurate. So again in turn, the valve opening in relation to pistion TDC is inaccurate as well. Compensate for that by using adjustable cam gear.
Very small matter really but when you are dealing with fuel (induction) charges and efficeint combustion inregards to picky performance tuning, small details matter.

[2oodoor]

Im bout an hour south of columbia im near charleston.

Im about 2.5 hr from ya then, Augusta GA right on the Carolina border. I go to Columbia all the time.

[stephensimmons]

Im about 2.5 hr from ya then, Augusta GA right on the Carolina border. I go to Columbia all the time.

Yea arnt you just north of I20 on 520?

[2oodoor]

Yea arnt you just north of I20 on 520?

383 & 20 , 520 makes a complete circle now connecting to 20 btw.. just opened new sc exit 6

I knew I saw the Summerville sign somewhere but couldnt remember. I was in N Chas in Dec. and got lost on a wrong turn. 213 a and b or something like that, it was dark and I wound up in Santa wonder land lights everywhere.. some kind of park. I was supposed to go the other way to embassy suites lol.

[stephensimmons]

383 & 20 , 520 makes a complete circle now connecting to 20 btw.. just opened new sc exit 6

Bout time they finished that! !ts been a while sence I been over there!

[stephensimmons]

still trying to get the larger pics.

[stephensimmons]

Ok here's the deal. I tore my a20a3 apart today. I wanted to build an 11.0 n/a motor. Well I ordered a new set of stock std bore(clevite) pistons for my rebuild and there the 8.8 compression ones not the 9.3 compression ones. I know the difference in the two is that the 8.8 engine had 110hp and the 9.3 engine had 120hp. No one makes the a20a3 pistons anymore which is the 9.3 compression pistons. The difference in the pistons is that the 8.8 has more of a dish than the 9.3 that hardly has any dish at all (ill post pics later when i get them cleaned up) also the 8.8 pistons has PJO stamped on the dome and the 9.3 pistons have PJOY stamped on it. What I wana know is should I install the new pistons or reuse my old ones sence ima shave my head .080 to get the 11.0 with the 9.3 pistons I should get 10.5 (sence there is a .5 difference in compression) with the 8.8 pistons which would be more friendly with the 93 octan than 11.0 plus ill have new pistons for when I do use my 50hp nos? :help:

[cygnus x-1]

Ok here's the deal. I tore my a20a3 apart today. I wanted to build an 11.0 n/a motor. Well I ordered a new set of stock std bore(clevite) pistons for my rebuild and there the 8.8 compression ones not the 9.3 compression ones. I know the difference in the two is that the 8.8 engine had 110hp and the 9.3 engine had 120hp. No one makes the a20a3 pistons anymore which is the 9.3 compression pistons. The difference in the pistons is that the 8.8 has more of a dish than the 9.3 that hardly has any dish at all (ill post pics later when i get them cleaned up) also the 8.8 pistons has PJO stamped on the dome and the 9.3 pistons have PJOY stamped on it. What I wana know is should I install the new pistons or reuse my old ones sence ima shave my head .080 to get the 11.0 with the 9.3 pistons I should get 10.5 (sence there is a .5 difference in compression) with the 8.8 pistons which would be more friendly with the 93 octan than 11.0 plus ill have new pistons for when I do use my 50hp nos? :help:


Would be cool to see a picture of the dish on these. Anyway, the first question is, how is the block? Does it need to be rebored? If so then you need oversize pistons and the ones you have are useless. The 9.3CR pistons should still be available from Honda in a slight oversize (0.3mm). IF the cylinders are too far out then aftermarket is the only option. Before you do anything else get that block checked.

If the block is still ok, check the stock pistons for wear. If they are ok too you could just put on new rings and go. Or if the block is ok but the old pistons are worn you could use the new ones. Although if that was the case I would return the Clevites and try to get the oversized Honda ones.


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[stephensimmons]

Would be cool to see a picture of the dish on these. Anyway, the first question is, how is the block? Does it need to be rebored? If so then you need oversize pistons and the ones you have are useless. The 9.3CR pistons should still be available from Honda in a slight oversize (0.3mm). IF the cylinders are too far out then aftermarket is the only option. Before you do anything else get that block checked.

If the block is still ok, check the stock pistons for wear. If they are ok too you could just put on new rings and go. Or if the block is ok but the old pistons are worn you could use the new ones. Although if that was the case I would return the Clevites and try to get the oversized Honda ones.


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The bore in the block is good and the pistons look good just they have 261,000 miles on them. this engine is being built so I can drive the car (and make it to the east coast meet in north carolina have a lil fun and make it back home) till I build my other a20a3 with forged pistons,rods,big valves,all ARP fasteners a GOOD set of headers and exaust and obd1 convertion.

[cygnus x-1]

The bore in the block is good and the pistons look good just they have 261,000 miles on them. this engine is being built so I can drive the car (and make it to the east coast meet in north carolina have a lil fun and make it back home) till I build my other a20a3 with forged pistons,rods,big valves,all ARP fasteners a GOOD set of headers and exaust and obd1 convertion.


If you're going to be building another engine with forged pistons and such then you might as well just throw in what you have now. With that kind of mileage I'm surprised the cylinders aren't worn. Hondas are reliable but that's a fair bit of miles.


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[stephensimmons]

If you're going to be building another engine with forged pistons and such then you might as well just throw in what you have now. With that kind of mileage I'm surprised the cylinders aren't worn. Hondas are reliable but that's a fair bit of miles.


C|

They are not perfect but ive seen worse and it has no ridge at all at the top of the cylinders ima just give them a good honing and insall the new piston and rings and a few other things. besides
I feel like if i do this one with the 10.5-11.0 compressions no one will be able to tell when i swap in my otha engine because ima use the same cam in both.

[MessyHonda]

yeah you wont get 11:1 comp on stock pistons...you will need to get some aftermarket ones...

[stephensimmons]

yeah you wont get 11:1 comp on stock pistons...you will need to get some aftermarket ones...

I read that if I shave .080 off the head that i would get 11.1. They say for every .040 you gain 1.0 in compression so if I go .080 I would gain 2:0. So ima go .080 off the head so that would give me 9.3 + 2.0= 11.3 with the pistons in there now but i bought the 8.8 pistons so that would be 8.8 + 2.0= 10.8. I git a couple of extra heads so ima go for the .080 shave!

[cygnus x-1]

I read that if I shave .080 off the head that i would get 11.1. They say for every .040 you gain 1.0 in compression so if I go .080 I would gain 2:0. So ima go .080 off the head so that would give me 9.3 + 2.0= 11.3 with the pistons in there now but i bought the 8.8 pistons so that would be 8.8 + 2.0= 10.8. I git a couple of extra heads so ima go for the .080 shave!


These were my estimations based on measurements of a stock chamber. I do have a chunk of a head that was cut up for research. I took off 0.080" and everything looks ok as far as the casting. One thing to watch for is the oil jet between cyls 2/3. It may be too long with the super milled head and might need to be cut down as well. Otherwise it should be fine.


Here's a picture:

http://bluegreenlabs.com/Prelude/Mods/HeadPorting/ChambersMilled2mm1.JPG



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[MessyHonda]

i would not shave the head that much...if you warp it you would have to replace it because it might not be safe to cut it up more...easyer to get high compression b18 pistons and get the pin on the rod bored out to 20mm to they can fit

[stephensimmons]

i would not shave the head that much...if you warp it you would have to replace it because it might not be safe to cut it up more...easyer to get high compression b18 pistons and get the pin on the rod bored out to 20mm to they can fit

Now thats a good idea! Wish i thought of this(or talked to you before bought the stock pistons and dropped th head off but i got two extra heads) Thanks for the idea Messy!

[stephensimmons]

Well this is what its all going in.
http://i754.photobucket.com/albums/xx186/stephensimmons/89a-3.jpg
well for some reason i cant up load pics

[2oodoor]

if you are using IE 8 you have to allow it thru pop up block , look at notice about 1/3 from top of screen. Its not pop up block but in the same place that notice comes in usually. then re try the image.

[cygnus x-1]

i would not shave the head that much...if you warp it you would have to replace it because it might not be safe to cut it up more


Actually you could probably skim off a few more thousandths than 0.080", but pretty much you're right. If you milled to 0.080" it would be mostly a one way trip. Although if you're going to this extreme then you probably aren't that concerned about long term reliability anyway.



...easyer to get high compression b18 pistons and get the pin on the rod bored out to 20mm to they can fit


Easier? I don't think so. And I wouldn't want to bore out the stock rods anyway. That spot is already the weakest link. Boring it out would make it weaker. It's also more expensive than simply milling the head.


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[stephensimmons]

Would be cool to see a picture of the dish on these. Anyway, the first question is, how is the block? Does it need to be rebored? If so then you need oversize pistons and the ones you have are useless. The 9.3CR pistons should still be available from Honda in a slight oversize (0.3mm). IF the cylinders are too far out then aftermarket is the only option. Before you do anything else get that block checked.

If the block is still ok, check the stock pistons for wear. If they are ok too you could just put on new rings and go. Or if the block is ok but the old pistons are worn you could use the new ones. Although if that was the case I would return the Clevites and try to get the oversized Honda ones.


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Here's the pic of the pistons you asked for. The one on the left is the 88-89 a20a3 9.3 compression piston and the one on the rightis the 86-87 8.8 compression pistons. You can see that the one on the left has less of a dish than the one on the right and thats what made the difference in compression. Also you will notice that the 8.8 piston has a PJO part number and the 9.3 piston has a PJOY part number. http://i754.photobucket.com/albums/xx186/stephensimmons/89c-2.jpg
http://i754.photobucket.com/albums/xx186/stephensimmons/89d.jpg

[cygnus x-1]

Here's the pic of the pistons you asked for. The one on the left is the 88-89 a20a3 9.3 compression piston and the one on the rightis the 86-87 8.8 compression pistons. You can see that the one on the left has less of a dish than the one on the right and thats what made the difference in compression. Also you will notice that the 8.8 piston has a PJO part number and the 9.3 piston has a PJOY part number. http://i754.photobucket.com/albums/xx186/stephensimmons/89c-2.jpg
http://i754.photobucket.com/albums/xx186/stephensimmons/89d.jpg




Excellent! I've never seen the lower comp pistons before now. This makes it obvious why the CR is higher in the later A20s. Cool stuff.


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[stephensimmons]

Excellent! I've never seen the lower comp pistons before now. This makes it obvious why the CR is higher in the later A20s. Cool stuff.


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The funny part it that both engines has a20a3 on them.