SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> Shaving down the head
/cgi-bin/YaBB.pl?num=1168649741

Message started by vroom1776 on 01/12/07 at 16:55:41

Title: Shaving down the head
Post by vroom1776 on 01/12/07 at 16:55:41

hey all,

If you shave a little bit of metal off of the head where it seals to the cylinder, you can raise the compression ratio.

I remember doing some calculations on HC pistons and cylinder volumes, but I couldn't find that post. Anyway, if one were to shave 0.1" off of the head (not necessarily a good idea, but maybe 1/2 as much?) the compression ratio would increase to about 10.2:1 (compared to stock ~8.5).

To do this... take off the head. get some grinding compound (e.g. alumina dust), and some oil, as well as a large piece of flat glass. Run the head around on there in figure 8s until you have removed as much material as you want.

All that being said (typed), I have not done this. It was suggested to me by a gear head friend of mine. keep in mind he wants to split the case and balance my flywheel, too...

Title: Re: Shaving down the head
Post by franch on 01/12/07 at 17:27:17

I did exactly that to get the warp out of my 65' 10hp wheelhorse tractor. holy*&%$#@ after that it flies. on hills where it used to bog down i go 1/2 throttle now.

Title: Re: Shaving down the head
Post by justin_o_guy on 01/12/07 at 17:28:32

In this post, there is a link,

http://suzukisavage.com/cgi-bin/YaBB.pl?board=RubberSideDown;action=display;num=1167758966;start=

In that article, an 80+ page pdf file, will be a section on shaving the head/getting more compression. According to that fellow, it gets quite a bit more complicated than just tightenning up the squeeze on the air & geiing more BANG outta the power stroke. But, if I was just the least bit more determined to get more outta the engine, that's where I would go to look for it. He said clean up the intake port, the exhaust, n ot as important. Eliminate steps between flanges & ports. Can't get the exhaust too straight cuz the ex valve spring pocket encroaches in the top of the port.

Have fun.

Title: Re: Shaving down the head
Post by vroom1776 on 01/12/07 at 17:30:57

... and I just had a thought on why this might not be the best idea, besides messing with the engine...

you will lower the very top of the engine. where the top engine mounts live. now you need top make a new bracket to fix the engine to the top of the frame. at least w/ a 0.100" drop... if you just went down 0.005" it'd prolly be okay...

Title: Re: Shaving down the head
Post by justin_o_guy on 01/12/07 at 18:20:01

If a guy has the savvy to get the thing apart, mod it, & put it together, getting some slack to line the hoes up won't stip him. Aww, heck, I would gpo back & fix rthat but Im pooped,, lol

Title: Re: Shaving down the head
Post by Ed_L. on 01/12/07 at 18:58:34

One of the reasons I've heard not to try shaving the head is that you will change the cam timing. I've even posted that reason a few times. You shorten the distance between the cam and crank by whatever thickness is shaved off the head which makes the cam chain longer which will change the cam timing. While reading this thread I suddenly realized that it might not be that much of a problem, after all when the cam chain gets older it will streach some and become longer which is the same effect on the chain as shaving the head. Since a higher milage savage still runs well with some streach in the chain isn't possible that the little bit of cam timing change caused by a shaved head would be a non-issue? Just a thought on it all, maybe I'm nuts but a shaved head might work after all.

Title: Re: Shaving down the head
Post by justin_o_guy on 01/12/07 at 23:05:26

The article by Tumi points oout the change in cam timing from shaving the head. He says it is retarded & that is good because it somehow allows the cylinder to fill better. IF I read it andIF I remember it as he intended. If I was messing with my engine at that level I would certainly read it agagin & most likely ask a few folks, too. I am not so sharp as to be able to see exactly WHy retarding the cam would allow a better charge. From where I'm sitting, the cam duration hasn't changed so the time the valve is open stays the same. NOW, what I can see is the piston has dropped further before it opens & may create a bigger vacuum & cause a strong rush of incomming air/fuel charge that will continue to pack itself into cylinder even after the piston starts back up. Since I don't know where the piston is when the valves operate I can't even hazard a guess at to how the cam timing will affect the running. The most comforting thought is provided by Ed, using common sense, noting the caM timing retards naturally & the bike runs & runs & runs.

Me? I just want one spare engine.& a few extra hundred $$$ , owell,, I've never had anything like this bike. It's fun to mess with. It's fun to ride. It has me associated with a bunch O folks who enjoy the same things, Dang folks, it's just good all around..

BTW, just started raining & it sounds GREAT!

Whatever you choose VRoom, I've done all I know for ya, that's give ya the link to that article. I know it's long, but there's a ton O stuff in there.

Title: Re: Shaving down the head
Post by Rockin_John on 01/12/07 at 23:51:26

How come nobody ever mentions the possibility of a high compression piston in these discussions of raising compression ratio? I know that Wiseco doesn't make one, and probably no other aftermarket performance parts maker currently makes one. But by some experimenting with modeling clay wouldn't a one-off be possible? Maybe by using another near sized piston as a starting point?

Title: Re: Shaving down the head
Post by YonuhAdisi on 01/13/07 at 04:36:34

Rockin_John wrote:

I've been wondering if a 94mm high compression VW piston would work.

Title: Re: Shaving down the head
Post by LANCER on 01/13/07 at 05:43:45

Does it fit the connecting rod/wrist pin perfectly?

Title: Re: Shaving down the head
Post by YonuhAdisi on 01/13/07 at 05:46:38

Don't know, it was just an idea I thought of when I found out that the Savage piston was 94mm. I have never had the opertunity to see the Savage piston and a VW piston side by side.

Title: Re: Shaving down the head
Post by Reelthing on 01/13/07 at 06:18:22

Rockin_John wrote:

How come nobody ever mentions the possibility of a high compression piston in these discussions of raising compression ratio? I know that Wiseco doesn't make one....

Well, there was a discussion a while back about Wiseco perhaps makeing a custom run for these bikes - I can not remember what the minimum number was - perhaps 50. If enough folks were interested - honestly interested seemed like a possible thing to do. I'd give a couple 95/96mm 9.5-10:1 a go

here it is:

http://suzukisavage.com/cgi-bin/YaBB.pl?board=RubberSideDown;action=display;num=1129657225

Title: Re: Shaving down the head
Post by vroom1776 on 01/13/07 at 07:35:43

yeah, I've been thinking about other things that could go wrong. It had not occured to me about the slack in hte cam chain... a large shave would be 0.1", as I suggested, effectiely lengthening the cam chain by 0.2", or 0.2"*25.4mm/inch = 5.8 mm.

Too much. Another issue I thought up: I don't want my piston to hit my valves. Depends on timing... and how much you shave off...

as implied above, there are no after market HC pistons presently available...

I read that article a year ago, and forgot most of it... :P

At any rate, I'm just trying to figure out CHEAP performance mods....

Title: Re: Shaving down the head
Post by Ed_L. on 01/13/07 at 17:04:40

I'm with you on a cheap performance mod, I'd think about a small head shave to get the compression around 9.5 to one along with a new cam chain. Don't know enough to do the math but it wouldn't be much of a shave. If you clean up the exaust port in the head, nothing major, just get rid of the angles and ridges to help the flow along with the shave I bet you could see a horse power or two overall. The only drawback would be swaping out the timing chain more often to compensate for the shorter distance between the cam and crank and chain streach. In theory it should work, gotta put some more miles on my '02 so it needs a "overhaul" ;D

Title: Re: Shaving down the head
Post by barry68v10 on 01/13/07 at 20:06:50

If you're gonna replace the piston, replacing the connecting rod or machining the current one to ensure it fits wouldn't be that big a deal. Any local machine shop should be able to handle the job. If you got a VW or Camry aftermarket piston, you'd want to take careful measurements to be sure. The last thing you want is an untimely (pun intended, you know it's about valve timing) contact between valve and piston.

Title: Re: Shaving down the head
Post by Rockin_John on 01/13/07 at 22:47:37

I didn't mean to have split the thread from the "head shaving" discussion, but there are some interesting ideas floating on both branches of the thread...

I know that shaving the head is a very old and time honored way to low bucks compression boost with pushrod engines, but as is being discussed, it brings with it possible chain length and cam timing issues. Though it still may be the easiest/best way.

It's been so long since I worked on V-Dubs that I'd forgotten about the 94mm piston possibility there. I haven't looked, but it would surprise me to find an existing piston with the right deck height (wrist pin to deck) and enough material on top to maybe mill some off for the 4-valve head. Unless as someone suggested, maybe a car like the Camery. Doesn't it alread have a 4-valve/cyliinder design? Bet the angle of the valves wouldn't be right though.

I don't know enough about metallurgy, but might it be possible to TIG weld some material on top of a Savage piston and then machine it back down? Or would it not survive the conditions inside the cylinder?

As Realthng said, if we could get enough people to commit to buying some, and get Wiseco to do a run of 50-100 pistons I'd be willing to up for at least one, maybe two depending on the price. Especially if they would make them available in a "one over" size.

Pardon me folk, but sometimes I just "think out loud."

Title: Re: Shaving down the head
Post by Reelthing on 01/14/07 at 01:19:09

in reading back on that other post - looked like the piston minimum order was 24 @ $112 (included rings and wrist pin) - 1 over size wasn't a problem according to the last info we had.

Title: Re: Shaving down the head
Post by YonuhAdisi on 01/14/07 at 02:47:50

Is that $112 each?

Title: Re: Shaving down the head
Post by Reelthing on 01/14/07 at 07:43:15

That was the price per each when the fellow called wiseco in 2005 - w/rings and pin - but the minimum order was for 24 - if the info was correct

* sorry went back and read the post - price was $122 *

Title: Re: Shaving down the head
Post by Rockin_John on 01/14/07 at 11:16:26

Reelthing wrote:

Sounds pretty reasonalbe to me.

The Wisco piston changes I've done in a couple of dirt bikes, the performace can change incredibly!

In fact, I'm kind of surprsed that the price is that low, and It may not be now. Looking at their web site, many of the pistons for muli-cylinder bikes cost $130+ each.

Title: Re: Shaving down the head
Post by wvhunter62 on 01/14/07 at 20:55:56

If you deside to do a group buy, I am in for at least 1 maybe 2. Twenty-four is a low minimum should be easy to achieve.

Title: Re: Shaving down the head
Post by justin_o_guy on 01/15/07 at 00:48:59

I wonder how many hard miles I need to get on it in order to justify a new piston?

Title: Re: Shaving down the head
Post by azjay on 01/15/07 at 06:30:04

justin_o_guy wrote:

I wonder how many hard miles I need to get on it in order to justify a new piston?

only a few,,,without oil :-[

Title: Re: Shaving down the head
Post by Savage_Rob on 01/15/07 at 07:42:58

[quote author=azjay link=board=RubberSideDown;num=1168649741;start=0#22 date=01/15/07 at 06:30:04]only a few,,,without oil :-[/quote]
Voice of experience.

Title: Re: Shaving down the head
Post by LANCER on 01/15/07 at 07:51:04

Amen.

Title: Re: Shaving down the head
Post by barry68v10 on 01/15/07 at 19:21:56

Quote:

I wonder how many hard miles I need to get on it in order to justify a new piston?

30-50k? My guess anyway, provided you keep the oil on the INSIDE of the bike ;D

Title: Re: Shaving down the head
Post by Greg_650 on 01/15/07 at 21:53:30

vroom1776 wrote:

This is all just for grins, right?

:)

If you're gonna shave anything you gonna take it to a shop to have it done, and you're certainly not taking off .100"...by hand on a piece of glass or any other surface.

A light polish like that might be okay on the head cover if you were using a compound or something, but a 1/10" is a bit much...or a 1/20" too.

Then you gotta worry about how much extra slack you're putting in the cam chain, and the change in the cam timing (as someone said).

You gotta remember the squish area, which is really small on the Savage engine. Plus ya gotta have clearance for those pesky old valves too...wouldn't want the old piston to smack 'em now :)

Title: Re: Shaving down the head
Post by verslagen1 on 04/04/07 at 21:55:58

For every .07" of chain stretch, you get 7° cam lag.

So unless you shave the cylinder by one chain pitch (.257") you're going to have to deal with it.

Or a little less would give cam advance... hmmm.

Food for thought ;D

Title: Re: Shaving down the head
Post by mpescatori on 04/05/07 at 04:24:48

vroom1776 wrote:

yeah, I've been thinking about other things that could go wrong...

At any rate, I'm just trying to figure out CHEAP performance mods....

If a cheap performance mod is what you're after, consider forced air intake.
Fit a highly flexible 40/50mm hose to the intake (like a vacuum cleaner hose) and guide it to the front of the bike, under the headlight; then attach a large funnel to it, anything between 4 - 6 " diameter. From a distance it'll look like a second headlight. Then take a test drive on the open highway and WOT.

In theory, the air funneled in should marginally supercharge the Savage; in practice, if done properly you should improve intake air pressure from an average 0.8 bar to around 0.9 to 1.0, thereby effectively supercharging the engine with a 0.1 - 0.15 bar increase in pressure.

At low speeds there would be no effect at all, at high speeds (beyond 60/70mph) ... you may need a 160 main jet, if there is such a thing...
...so you'd be running rich at low speeds, and better and better as speed increases...
...maybe lean beyond 110mph...

Title: Re: Shaving down the head
Post by justin_o_guy on 04/05/07 at 14:57:21

I've been thinking about the cxam chain length being affected by head/deck shaving. IF there was no chain tensioner then the slack would be on the back side & the chain would actually appear shorter, since the cam & crank are closer. The tensioner only pulls the slack out & I am starting to think the whole"Makes the chain appear l;onger & retards the cam" idea may be bass akkerds. Anyone clear me up on this? OHHH Wait a MINute,, wait a MINute! I got it. It just came thru in a picture. As the head is lowered, the cam axis is closer to the crank, & the crank has to rotate far enough to remove that slack before the cam will turn, so it is retarded that far. SO, (using large numbers for illustration, not even close to acceptable mods) If ( really BIG if) we cut 1/2 inch off the head, the circumference of the crank gear would have to move 1/2 inch before the cam would start to turn. The tensioner woiuld have to soak up a whole 1" of slack. IF ( another Big If) the circumference of the crank gear was 6" then the 1/2 inch slack would translate to 1/12th of the O.D. & be 30 degrees retarded. So, all we need to do is use correct numbers & the amount it is retarded is there. Is this correct? Note, since I am just starting to get my head around this, I am not gonna be surprised if I am wr,, wr,, wr,, incorrect..

Title: Re: Shaving down the head
Post by memetr on 06/21/07 at 13:07:06

Guys there is a specific formula used to raise compression by head milling. This is a cheaoer method than new piston. Harley sportster guys use this method all the time.

Title: Re: Shaving down the head
Post by Reelthing on 06/21/07 at 14:15:13

difference is the HDs are push rod motors not ohc engines

Title: Re: Shaving down the head
Post by Ed_L. on 06/21/07 at 16:46:33

The only way that I can think of to advance the timing gear to compensate for shaving the head would be a offset key between the cam and gear. Don't know if there is enough room to fit a offset key in there or not but I've seen them used for other applications. Just a thought.

Title: Re: Shaving down the head
Post by verslagen1 on 06/21/07 at 17:40:58

http://i21.photobucket.com/albums/b277/gmdinusa/CamChainGraphic.jpg
Graphic by Greg

I calculated that for .07" chain stretch it would retard the timing by 7°.

I beleave Justin's right, shaving the head will make the chain seem longer. So the same calculation applies.

Title: Re: Shaving down the head
Post by LANCER on 06/21/07 at 18:28:23

We shall see what happens soon.

Title: Re: Shaving down the head
Post by Max_Morley on 06/21/07 at 21:58:08

Or redrill the cam gear 83 degrees (or whatever it takes to get the cam back in time with the crank) from where it is now. Seems like I remember Crane Cam gears with 3 sets of holes and marks for Std, adv and retard depending on what kind of performance chages yo were looking for.