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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Compression ratio/head skim /cgi-bin/YaBB.pl?num=1200805437 Message started by KwakNut on 01/19/08 at 21:03:57 |
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Title: Compression ratio/head skim Post by KwakNut on 01/19/08 at 21:03:57 Compression on these things seems waaay low - I'm feeling too lazy to reassemble my valvetrain and see how much valve to piston clearance I have, so can anybody tell me how much can be skimmed safely off the head without having to recess the pistons for valve clearance? |
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Title: Re: Compression ratio/head skim Post by YonuhAdisi on 01/19/08 at 21:37:01 I would actually like to know that as well. Next time I need to go into the engine, I would like to shave the head. |
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Title: Re: Compression ratio/head skim Post by Oldfeller2 on 01/19/08 at 22:24:41 Shaving the head moves your cam gear down towards the crankshaft. What will amaze you is that the head shave amount hits cam chain "slack factor" with a 2x multiplier and it, by itself, could take out most of your chain adjustment service life. Horsepower is an elusive animal, more is nice but at what cost? Check into nitrous if you want low cost serous hp -- low cost until you start seeing what nitrous stresses will do to your clutch and transmission that is. ;) |
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Title: Re: Compression ratio/head skim Post by KwakNut on 01/20/08 at 04:33:08 70535B595A53535A4D0D3F0 wrote:
Several hundred pounds for a nitrous system isn’t cheap for a little extra torque compared with £20 to skim the head. That aside, I don’t want to nitrous this bike – I could put some spare solenoids on it if I wanted to, but I just want a bit more grunt for normal daily use. I just want the engine to run a little more efficiently, so I’ve ported the head, I’m using free flow air filter, modding the carb and I’m going to skim the head. I looked at the possibility of welding up the combustion chamber, but that’s not an option of a 4-valve pent roof. I’m aware that, as with all engines with chain driven overhead cams, there will be an effect on the cam chain and timing – easy answer to the timing is to modify the cam gearwheel so the cam timing can be dialled in. As for the extra slack in the chain – that’s manageable. Now, back to the question – can anybody answer how much material can come off the head before the pistons need pocketing for valve clearance? |
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Title: Re: Compression ratio/head skim Post by demin on 01/20/08 at 05:13:33 Can't answer your question,but maybe an alternative.Domed piston? |
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Title: Re: Compression ratio/head skim Post by klx650sm2002 on 01/20/08 at 05:26:53 Has anyone skimmed the top of the barrel. Clive W :) |
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Title: Re: Compression ratio/head skim Post by Savage_Greg on 01/20/08 at 06:01:55 393E2A646762213F60626260520 wrote:
Not that I know of... |
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Title: Re: Compression ratio/head skim Post by KwakNut on 01/20/08 at 06:04:53 65646C686F010 wrote:
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Title: Re: Compression ratio/head skim Post by KwakNut on 01/20/08 at 06:10:56 645146447C151613230 wrote:
Not that I know of...[/quote]It's quite common on lots of bikes and cars to do it this way, and it makes sense. Take a minimum skim off the head just to clean up the mating surface, then take most of the material from the cylinder top - that way you reduce the squish area gap, which is good for mixture distribution. In the Savage motor there's 4mm between the top of the piston and the squish face of the head - way too much to really squeeze the gas and push it around the chamber, I'd rather it was about 1.5-2mm, but there's no way I could take 2-2.5mm from the barrel! Before anybody says try a longer rod . . . . . I'm not going to split the bottom end, so forget that! |
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Title: Re: Compression ratio/head skim Post by T Mack 1 on 01/20/08 at 08:29:58 KwakNut, Not sure if it helps in your search for power, here's a link to photo's I posted of the split lower end. Fairly low tech engine. Also has pict's of why I split it. (to look for metal shavings & clean it.... :P ) http://suzukisavage.com/cgi-bin/YaBB.pl?num=1185890273/0#0 T Mack |
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Title: Re: Compression ratio/head skim Post by smokin_blue on 01/20/08 at 16:07:16 1D283F3D056C6F6A5A0 wrote:
Not that I know of...[/quote] Might want to ask Lancer on that one...... ;) I think he is lurking lately... ;) |
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Title: Re: Compression ratio/head skim Post by verslagen1 on 01/20/08 at 16:49:12 203E3C383A3D0C313F2636530 wrote:
I'm quite sure he's made a list and is checking it twice for nary a savagite will sleep tonight waiting for a special cam chain, their sidewalks are shoveled and the mail box de-iced, their wrenches are laid out, and they hope they are not vain, their head and clutch covers are all shiney and clean, Some are glad they sprung for a performance cam, While some wish they could and others say I can barely hang on now, But I'm sure Lancer would say 'to each his own, and to all a super chain'! |
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Title: Re: Compression ratio/head skim Post by justin_o_guy2 on 01/21/08 at 00:06:22 There wqs talk of a piston group buy. I dont know if it died, happened or is pending. |
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Title: Re: Compression ratio/head skim Post by klx650sm2002 on 01/21/08 at 02:26:07 8.5:1 - 9.5:1 should give 3.2% more torque and 8.5:1 - 10.5:1 should give 6% more torque. Clive W :) |
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Title: Re: Compression ratio/head skim Post by LANCER on 01/21/08 at 07:53:32 6B786F6E717C7A78732C1D0 wrote:
I'm quite sure he's made a list and is checking it twice for nary a savagite will sleep tonight waiting for a special cam chain, their sidewalks are shoveled and the mail box de-iced, their wrenches are laid out, and they hope they are not vain, their head and clutch covers are all shiney and clean, Some are glad they sprung for a performance cam, While some wish they could and others say I can barely hang on now, But I'm sure Lancer would say 'to each his own, and to all a super chain'![/quote] HO HO HO ....... MERRY CAM CHAINS ....... HO HO HO |
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Title: Re: Compression ratio/head skim Post by LANCER on 01/21/08 at 07:57:03 HAD THE HEAD SHAVED 0.015" (limited due to head/cyl bolts) CYLINDER SHAVED 0.035", FOR A TOTAL OF O.O40" I GOT A MSG FROM ANOTHER MEMBER WHO SAID THAT THIS WOULD RESULT IN A 9.15 to 1 compression ratio. |
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Title: Re: Compression ratio/head skim Post by smokin_blue on 01/21/08 at 09:34:40 6F626D6066713134030 wrote:
Don't want to be too anal but for those plucking numbers and running away with them I believe the 0.015 +0.035 = 0.050 not 0.040. :-[ |
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Title: Re: Compression ratio/head skim Post by Mr 650 on 01/21/08 at 10:03:56 does the head gasket figure in? |
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Title: Re: Compression ratio/head skim Post by LANCER on 01/21/08 at 19:05:52 3B2527232126172A243D2D480 wrote:
Don't want to be too anal but for those plucking numbers and running away with them I believe the 0.015 +0.035 = 0.050 not 0.040. :-[/quote] Sorry, that was a typo on my part, it is supposed to be 15 & 25 thou. for a total of 40 thou. |
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Title: Re: Compression ratio/head skim Post by metri on 01/25/08 at 19:49:04 LANCER wrote on 01/21/08 at 18:57:03: Quote:
Is there anyway around this to be able to shave the head enough to get the compression to 9.5:1 ? LANCER wrote on 01/21/08 at 18:57:03: Quote:
That's about 1mm overbore I guess... Do you think it's safe to overbore 2mm? How much wall thickness would be left with .080" bored out? ( think 1mm is 39.5 thou, but I may be off. I found 2 sizes of oversized pistons for sale, 1mm over and 2mm over...) Thanks |
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Title: Re: Compression ratio/head skim Post by KwakNut on 01/26/08 at 04:15:54 6F6776706B020 wrote:
That's about 1mm overbore I guess... Do you think it's safe to overbore 2mm? How much wall thickness would be left with .080" bored out? ( think 1mm is 39.5 thou, but I may be off. I found 2 sizes of oversized pistons for sale, 1mm over and 2mm over...)Thanks[/quote]The mm conversion figure is 39.4 (– actually 39.37 but we’re not to less than a tenth of a thou with bike work!!). Skimming 35 thou off the cylinder (without touching the head) will take you to 8.99:1. Upping the bore to 95mm would give you 8.61:1 if you change nothing else. Remember that there’s 4mm of free cylinder above the piston, so if you up the bore you also up the unswept cylinder volume and therefore the total compressed volume (chamber + gasket thickness + unswept cylinder volume). Up the bore to 95mm and skim 40 thou, and you’ll be up to 9.29:1. Taking metal off the top of the cylinder has greater effect than taking metal off the head, because part of the head at the sides of the chamber is metal to provide squish – the effect of skimming the head is reduced by the percentage of the bore area which faces solid metal rather than open chamber. http://i43.photobucket.com/albums/e367/5000SE/Compressionarea.jpg To get to 9.5:1 you’ll need to remove 58 thou through a combination of head skim, cylinder skim and gasket thickness. I haven’t confirmed the valve to piston clearance on the Savage. Being a low compression engine (and low revving ie little cam overlap) it may not be a great problem, but don’t bet on that when you’re potentially bringing the valves a full 1.5mm closer! 58 thou is a lot of metal to remove – 1.5mm of slack on both sides of the timing chain – so you’d have an extra 3mm of chain to deal with through the Savage’s already struggling cam chain tensioner. Re-profiling the tensioner guides will help a little, as will slotting the cam wheel so you can dial in the correct cam lobe timing to compensate for so much chain adjustment, but I think of you go more than about 1mm of skim you’re opening up a real Pandora’s box of problems unless you have a workshop in your own back garden, plenty of machinery in it and a lot of spare time!! Skimming is a great answer on pushrod engines – just shorten the rods to keep the valvetrain geometry as it should be – but with overhead cams it can get ugly. If you want to go for anything more than a mild CR increase and thin skim with the Savage you’re going to need a high compression piston. I’ve looked around and can’t see anybody listing them – I considered ordering up a one-off, but is it worth the cost in terms of dollars per horsepower? |
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Title: Re: Compression ratio/head skim Post by KwakNut on 02/01/08 at 11:06:45 Just had my barrel skimmed by 40 thou - the machine shop was reluctant to grind the head as they were worried about clamping on fins and snapping some off. I still need to clean up the head face - guess it's down to old school work with file, straight edge and fine abrasive paper. The bore and piston were in almost as-new condition, guess that's how they should have been on an 8000 mile motor. I'll cc check the cylinder and head chamber before assembly to be 100% sure of compression - you never know if Suzuki quoted it accurately in the first place. Soon be reassembling then wait for Lancer's cam to arrive to finish the top end. http://i43.photobucket.com/albums/e367/5000SE/Cylinderpostskim.jpg |
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Title: Re: Compression ratio/head skim Post by LANCER on 02/02/08 at 05:53:52 The reason for the 15 thou off the head : 1. to be sure that the head was perfectly flat, & 2. there is a hard limit due to a head/cyl bolt head that is between them & 3. the squish area. I choose to try the shaving vs a new piston due to the cost of a new piston and cyl... if I were going with a new piston I would also bump it up to the 97mm size and would need to bore the cyl to match AND have the silicone carbide treatment done. My current cyl has the silicone carbide already and I am not going to just cut that away for a bigger piston, I would use a different cyl for the 97mm piston. |
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Title: Re: Compression ratio/head skim Post by KwakNut on 02/02/08 at 07:24:50 [quote author=323F303D3B2C6C695E0 link=1200805437/15#22 date=1201960432]The reason for the 15 thou off the head : 1. to be sure that the head was perfectly flat, & 2. there is a hard limit due to a head/cyl bolt head that is between them & 3. the squish area. quote]I'd much prefer it if the machine shop had agreed to take 10 thou off the face and 30 thou off the cylinder for me, but te were reluctant to clamp the head fins. 1. I'll have to live with the head not being skimmed, and dress the head face by hand. Done that before a few times and will just have to do it again, thought it's a painstaking job. 2. I may come to discover that limit - though whether the material comes off the top of the cylinder or under the head should make little difference to any clearances as long as the total amount skimmed is the same. 3. The squish are on the Savage is too thick - about 4mm between the top of the piston and the head face. I'd rather see it down to 2-2.5mm, but taking the full 40 thou off the cylinder reduces it to 3mm, which will give far more effective squish. Have to agree on the bore/piston view - not worth it. |
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Title: Re: Compression ratio/head skim Post by justin_o_guy2 on 02/07/08 at 06:05:16 I will likely inspire some of the knowledgable ones to laugh long & hard, but, I gotta ask. How hard would it be to use a piece of heavy glass to put sandpaper on to dress the head down? I know how much time I put into little things that wont begin to repay me with power, this would at least pay back with something tangible. I GOTTA learn how to do pics, you folks would get a kick outta the way the shop is coming along, sloooow, BUt man, CHEAP! Hey,, What is the deal with the bolt that limits the head skim to .015? Is it the length of the bolt or is there a bolt head in the way? If it's the head, couldn't it be cut down a bit? Or, is .015 about as far as the head should go anyway? Reprofiling the chain guides helps some, I guess, but I reprofiled mine when I did the chain, still had 8 mm of tensioner extension with the new chain, kinda irritated me >:( If I was gonna do the cylinder & head work I might look at modifying the guides. Instead of just reprofiling, I might look at adding a thickness of good plastic, like a piece of cuttingboard. That stuff is tough & slick, dunno how it would handle the heat, but it would bear a looking at. |
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Title: Re: Compression ratio/head skim Post by KwakNut on 02/07/08 at 07:46:23 627D7B7C61665767576F7D713A080 wrote:
Not sure what you mean about using plastic, but in answer to using a glass plate and abrasive paper to clean up the mating faces, the answer is yes you can. I've done that before using thick glass, also using a ground steel workslab. It's relatively straightforward, and you can check the head for square as you do it - tends to give very good results. On some 2-stroke applications it used to be common to completely remove the head gasket and instead lap the barrel/head mating with grinding paste to make the seal airtight without a gasket. Sounds silly, but it worked. |
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Title: Re: Compression ratio/head skim Post by justin_o_guy2 on 02/07/08 at 10:30:36 Doesnt sound silly to me, no gasket is good stuff. Re: Plastic, Just reprofiling the guides doesnt seem to be enough to actually "soak up" the slack in the chain, since a new chain, old guides, no skimming anywhere, left me with the tensioner extended 8 mm. I am thinking that the guides could be built up a bit, using a piece of plastic. It would be hazardous, because it might get loose. I can't imagine attaching it without rivets. I would be scared the whole time I was running it, it would require regular inspections till it became obvious it was gonna make it or not. I think the plastic used for cutting boards would be good, unless it wont handle the heat. |
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Title: Re: Compression ratio/head skim Post by KwakNut on 02/07/08 at 13:56:38 7B646265787F4E7E4E76646823110 wrote:
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Title: Re: Compression ratio/head skim Post by verslagen1 on 02/07/08 at 16:00:19 1F23353F1A2120540 wrote:
1st plastic behind the guide ain't going to do you a bit good, unless you are referring the front guide. And this is an idea because you're planning to skim the head. This will retard the cam timming a bit. I figured out that .07" chain stretch will give almost 7° retard on the cam. So .01 equals 1° retard. How much bulge to counteract that? Don't know. 2nd reprofiling the rear guide will take up alot of slack if done right. What he did to reprofile wasn't detailed other than he bent it. The only issue I have with this is the plastic has shed off a couple of these guides. Putting a bow in something with molded on plastic in my book is to risky. Take an old one, strip off the plastic, and replace it with a block of delrin. Shape it to your hearts content. There are quite a few bear quality plastics being invented lately, so do some research, go to a plastics distributer, not the guy behind the counter but someone qualified to pick a plastic for you. Delrin is a common plastic, not what is considered a bearing plastic, but for a chain guide maybe ok. I doubt the plastic on their is of better quality. |
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Title: Re: Compression ratio/head skim Post by KwakNut on 04/23/08 at 06:14:03 It's taken me a while but the motor is going together. Interestingly, but not surprisingly, Suzuki's quoted factory compression ratio was a little out. With a 0.8mm head gasket and chamber volume measured at 53.3cc, original CR would actually have been 8.53:1. Taking 40 thou off the barrel should have taken my CR up to 9.2:1 - and at first it did when I fitted the gasket and put her together. However, I had a problem with torquing up the head bolts and had to take the head and barrel back off to re-set the bolts in the block, and when I did, I fitted a new head gasket (£28/$55 just for the head gasket alone from the Suzuki rob shop!!). The new Suzuki gasket was actually 0.56mm instead of 0.8 – and that makes some difference. Quite surprising, because the gasket I took out was .8mm and the pattern replacement I originally fitted was also .8mm – maybe Suzuki have changed the spec since. So, with the new gasket, CR for the rebuilt motor is 9.37:1. Should hopefully be good for a few percent more bang per stroke, and coupled with the other engine mods should give the Savage more guts. Of course, timing geometry is affected, but not so much as you’d think: Between the skim and the head gasket there will be 1.26mm less distance between cam chain gears, or 2.52mm extra cam chain slack overall. Now, a new cam chain is 127.0mm for 21 pins centre to centre, service limit is 128.8mm, 1.8mm wear for 21 pins. With the chain being overall about 5 times that long, that means the tensioner/cam timing is okay to deal with about 9mm of slack in the cam chain, so the head skim just reduces my allowable cam chain wear down to about 6.5mm. My wear limit per 21 pins will be 1.3mm instead of 1.8mm. Hopefully not a problem with one of the new cam chains with nitrided pins – I was going to slot the cam gear to compensate for the skim, but not necessary! |
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Title: Re: Compression ratio/head skim Post by verslagen1 on 04/23/08 at 07:24:39 I went thru the cam chain geometry last year, and calculated the for every 0.01" of chain stretch you'd have 1° of cam retardation. There is a pin to lock the cam to the gear besides the bolts. You could flip the gear over and have it redrilled for the amount of advance you need. |
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Title: Re: Compression ratio/head skim Post by KwakNut on 04/23/08 at 08:33:45 Sounds about right. For others who are curious, the cam wheel is about 3” diameter at the chain pins, so one degree will be about .026” at the circumference. There are about 52 pins in the chain between the two wheel centres, so .026" of stretch in the length of chain between crank and cam wheels would come from a shade over .010” wear per 5”/21 pins. A degree or two may not be much in terms of cam timing on a low-revving lump. If .010” will affect timing by 1 degree, then an old chain at factory recommended wear limit (1.8mm / .071”) will affect timing by 7 degrees – puts things into perspective. Good point though when you add skim to the equation – the barrel skim and thinner gasket generate an extra 1.25mm on the straight side of the chain which will cause 2 degrees retardation of the cam, to which you then start adding wear. I originally considered slotting the cam wheel to dial in the cam in the Savage, but decided against it. I may revisit that decision, slot the screw holes and re-drill a fresh dowel somewhere to give me about 3 degrees of advance, 2 degrees to compensate for the skim and maybe another one for initial chain wear. I bet that gear is hard too – might have to grind through the surface with a Dremel before a drill can cut it. Or, if I’m lucky I may be able to find about half a tooth of change by flipping the wheel – I’ll look into it at the weekend. |
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Title: Re: Compression ratio/head skim Post by verslagen1 on 04/26/08 at 10:31:00 Kwak, thou repeath thy self. .250 between pins? right so jump a tooth equals 9.6° So with a stretched chain you could adjust for the stretch and get 5° advance. |
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Title: Re: Compression ratio/head skim Post by KwakNut on 04/26/08 at 12:57:06 2D3E2928373A3C3E356A5B0 wrote:
38 teeth on the wheel, so it's 9.47 degrees per tooth. I wanted to make up for the 1.86 degrees of retard the barrel skim was going to give me. I used a Dremel to oval the screw holes and fitted a new cam stud 182 degrees out from the original. I decided I was more interested in bottom end torque and good starting than top end, so didn’t want extra advance. However, the 182 degrees ended up being 182.3, so it now has 0.45 degree advance over standard after the barrel skimming, half a degree for luck! http://i43.photobucket.com/albums/e367/5000SE/LSCamwheelnewpos.jpg |
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Title: Re: Compression ratio/head skim Post by verslagen1 on 04/26/08 at 13:07:37 The heat treatment is clearly visible on your gear, was the work hard to do or normal? |
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Title: Re: Compression ratio/head skim Post by KwakNut on 04/26/08 at 13:22:52 4B584F4E515C5A58530C3D0 wrote:
I used the dremel to grind the top 20 thou off the gear face before I started drilling - drill then went in no problem, though it felt like it was snagging a little coming through the case hardening on the other side, but drilled fine. On the cam side it was only opening up the original hole from 5mm to 5.5, so that was no problem. |
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Title: Re: Compression ratio/head skim Post by KwakNut on 05/05/08 at 15:53:32 Well, Lancer's uprated cam chain is fitted, head cover is on and top end is assembled, timing is set up. But . . . that extra 0.1" of slack in the chain from .040 head skim and thinner gasket has the tensioner extended this much with a brand new camchain: http://i43.photobucket.com/albums/e367/5000SE/DSC00651.jpg I may just have to do the Verslagen tensioner mod after all! |
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Title: Re: Compression ratio/head skim Post by BurnPgh on 10/03/11 at 16:12:28 bump from the dustbin of history I've been considering this head skim idea but as far as the timing retard/advance is concerned...it seems a fair amount of effort was put into calculating and drilling the cam sprocket. Wasn't EdL able to, around this same time, advance the timing 4* (more than needed for this skim) by simply ovaling the holes for the pickup? |
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Title: Re: Compression ratio/head skim Post by verslagen1 on 10/03/11 at 16:38:29 7245425E605758300 wrote:
That was for the ig timing. skimming the head will retard the cam timing. 2 different issues. You'd need to oval the cam sprocket and create some method to keep the adjustment. 1 thought I had, you can redrill the 1 o'clock hole on the opposite side and oval the mounting holes for a fixed advancement of a certain angle. |
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