SweetBadger 94 Posted January 19, 2006 I've just gotten my MI head back a local machnist/rebore centre, and I'm not too happy with the results. The head face didn't look too bad before I sent it off to them but to be on the safe side I sent it to be checked and skimmed if necessary. They've skimmed it alright! I've just measured it (crudely - with a steel rule/set square with 0.5 mm markings) and it is definitely below 131.5 mm (closer to 131mm) . Also as you can see from the pics, it hasn't exactly come back smooth, you can see every pass the machine tool made! It also came back with machining debris in every orifice of the sodding head which is going to take a lot of cleaning if the head can be used... Rough face? Almost machined into the valve seats! I've read conflicting posts on the minimum height of an MI16 Head, would it be possible to use this head with the thicker headgasket and an increased CR, or should I just get on to the machinist and tell em they've been rather inept and fooked the head! Share this post Link to post Share on other sites
petert 586 Posted January 19, 2006 That will be fine. Why didn't you get it hot tanked at the same time? Share this post Link to post Share on other sites
SweetBadger 94 Posted January 19, 2006 That will be fine. Why didn't you get it hot tanked at the same time? Oh nice one! Yeah probably should have done to save me some time, but a bit of degreaser and some elbow grease should have it cleaned up! I've cleaned the block by hand (bloody nightmare, getting 15 yrs worth of oil/grease off without making too much mess in my girlfriend's dad's shed!) so the head shouldn't be too bad by comparison... Thanks, Alex. Share this post Link to post Share on other sites
SweetBadger 94 Posted January 19, 2006 Just out of interest what do you reckon is the minimum safe height you can skim an MI head to? Is it limited by a too high CR, machining into valve seats or Piston/Valve contact? Share this post Link to post Share on other sites
pug309twin40s 1 Posted January 19, 2006 that will be okay. i had a mi16 cyl head with about the same as yours skimmed as was fine. the roughish surface will help the cyl head seal to the headgasket. Share this post Link to post Share on other sites
PumaRacing 2 Posted January 20, 2006 that will be okay. i had a mi16 cyl head with about the same as yours skimmed as was fine. the roughish surface will help the cyl head seal to the headgasket. It most certainly won't and that must be one of the worst and most dangerous old wive's tales that ever circulates about how to build engines. Modern gaskets and modern high performance engines require very fine surface finishes, especially on the aluminium components. Even if the basic premise were true, which it isn't, there's a big difference between a uniformly rough (or smooth if you prefer) surface with no inclusions machined to a specific RA finish and a shiny one with deeper tool marks across it for the combustion gases to go down. In fact I would say that most jobbing machine shops don't even have the right equipment to achieve the optimum finish on heads and blocks which is why the first thing I bought when I set up 15 years ago was my own mill and a custom made flycutter so I could achieve those finishes on race engines. The first race engine I ever built back then was an MGB one for a customer who had raced the car for 6 years but never won a race and never lasted more than a few races before a head gasket went. He'd tried different machine shops, standard gaskets, copper asbestos ones and even custom made solid copper ones but everything blew eventually. In fact the reason he came to me for a new engine because a gasket blew on the rolling road when he was having the latest engine set up and damaged the block. With the perfect surface finish on the block and head, a standard Payen gasket and standard head studs and nuts the engine I built for him never blew another gasket or had any other sort of failure and set four new UK circuit records in its first season. All he had ever really needed was good quality standard components and the right machining. Well another 20 bhp over what he'd previously had helped but that came from flow bench work and attention to detail rather than gasket finishes. Like anything to do with engines each supposedly tiny subject, of which you need to understand hundreds to build an engine to a perfect standard, could entail years of research and study into the optimum techniques, shapes and finishes. Frankly a lifetime just isn't enough. If you want someone else's professional view on it you can read this. http://www.babcox.com/editorial/us/us80222.htm If you want to see what the correct aluminium surface finish on a modern high performance engine should look like after machining you need to find something like a brand new Honda VTEC cylinder head or even one off a humble Ford Zetec. You can nearly see your face in it. What the jobbing engine reconditioning trade churn out for the average punter is a bloody joke in comparison and frankly most of those places should be avoided like the plague. Share this post Link to post Share on other sites
petert 586 Posted January 20, 2006 (edited) Sometimes you can see a change in direction from a cutter but it's not measurable. If you can feel changes in the surface with your fingernail, take it somewhere else to be repaired. Edited January 20, 2006 by petert Share this post Link to post Share on other sites
Higgy 0 Posted January 20, 2006 Looks rough to me. Seems that there are deeper marks on one side than the other? Engineer with machining experience in my office, thought maybe cutter was not level. Looked like a single flycutter instead of multi-head flycutter? This is the finish the machine shop at work achieved for me - My head (0.25mm removed) Regarding the swarf, there is no real way of stopping it getting everywhere, just need to spend (alot) time cleaning, an air line is useful. For the surface finish, an Ra of 1.6 (or N7) is classed as use for static mating surfaces? Of the 2 headgaskets I've bought from PartCo, they have both been the thicker (1.4ishmm) ones. I guess if you want a headgasket, most likely the heads been skimmed nowadays. Higgy. Least your valve seats look ok, took me ages lapping mine in Share this post Link to post Share on other sites
mfield 20 Posted January 20, 2006 Looks rough to me. Seems that there are deeper marks on one side than the other? Engineer with machining experience in my office, thought maybe cutter was not level. Looked like a single flycutter instead of multi-head flycutter? This is the finish the machine shop at work achieved for me - My head (0.25mm removed) Regarding the swarf, there is no real way of stopping it getting everywhere, just need to spend (alot) time cleaning, an air line is useful. For the surface finish, an Ra of 1.6 (or N7) is classed as use for static mating surfaces? Of the 2 headgaskets I've bought from PartCo, they have both been the thicker (1.4ishmm) ones. I guess if you want a headgasket, most likely the heads been skimmed nowadays. Higgy. Least your valve seats look ok, took me ages lapping mine in Why do you valve seats look closer to the edge on the middle two ? Is it just a trick of the light or normal ? Share this post Link to post Share on other sites
SweetBadger 94 Posted January 20, 2006 Looks rough to me. Seems that there are deeper marks on one side than the other? Engineer with machining experience in my office, thought maybe cutter was not level. Looked like a single flycutter instead of multi-head flycutter? This is the finish the machine shop at work achieved for me - My head (0.25mm removed) Regarding the swarf, there is no real way of stopping it getting everywhere, just need to spend (alot) time cleaning, an air line is useful. For the surface finish, an Ra of 1.6 (or N7) is classed as use for static mating surfaces? Of the 2 headgaskets I've bought from PartCo, they have both been the thicker (1.4ishmm) ones. I guess if you want a headgasket, most likely the heads been skimmed nowadays. Higgy. Least your valve seats look ok, took me ages lapping mine in Right, well after seeing your head looking nice and smooth they've obviousy done a bit of a sh*t job on mine! With regards to the roughness of the head, obviously I can't measure the Ra, but if I run my finger nail over it, although I can't feel any cutting mark in particular, I can hear a high pitched sound from it rubbing in the grooves! So the height is not so much of an issue, even if they did skim it below spec without telling me, but I'm not going to use it if the head gasket isn't going to last. There's another engineering firm near me which look reputible. I'll get it check out there and see if they can do anything with it. I also let them loose on my crank for a complete regrind, hope they haven't cocked that up too . Thanks for the replies. Share this post Link to post Share on other sites
SweetBadger 94 Posted January 20, 2006 Why do you valve seats look closer to the edge on the middle two ?Is it just a trick of the light or normal ? Well it's not a trick of the light, there does seem to be a difference between the clerance of the valve seats and the head face. I'm not sure whether this is normal, but I would have thought the seats should be set at the same depth. Hope they haven't skimmed the head at an angle aswell! If I get a report from another engineering company saying its knackered, what do people reckon are my chances of getting some compensation? I've got a feeling I'm gonna have to put this down to experience, as its probably cheaper to get a replacement head rather than waste time and money chasing this up... Share this post Link to post Share on other sites
PumaRacing 2 Posted January 20, 2006 Right, well after seeing your head looking nice and smooth they've obviousy done a bit of a sh*t job on mine! With regards to the roughness of the head, obviously I can't measure the Ra, but if I run my finger nail over it, although I can't feel any cutting mark in particular, I can hear a high pitched sound from it rubbing in the grooves! So the height is not so much of an issue, even if they did skim it below spec without telling me, but I'm not going to use it if the head gasket isn't going to last. There's another engineering firm near me which look reputible. I'll get it check out there and see if they can do anything with it. I also let them loose on my crank for a complete regrind, hope they haven't cocked that up too . Thanks for the replies. No need to get it reskimmed and risk even more damage. Teach yourself some real engineering instead. Get a block of nicely flat wood (planed not just sawn) about 7" x 2.5" by an inch high and a couple of sheets of medium wet and dry paper. About 180 to 240 grit will do the job, and some paraffin. Wrap a sheet of w&d round the block and keeping it wet with paraffin work the head surface in random patterns making sure you cover all the area evenly. All you're really trying to do here is take maybe a quarter to half a thou off to improve the cutter marks so you won't destroy any flatness limits the gasket needs. What you should end up with is a lovely 'ground' sort of surface finish which is actually very smooth but not shiny. Just the ticket for modern gaskets actually. You've also made a tool and acquired a skill which you can use on heads and blocks in future to show up any low spots, remove the last bits of old gasket residue and save skimming costs most of the time if the surface is generally ok. Sometimes I have to skim really manky corroded heads and as you might know aluminium corrosion is aluminium oxide which is very hard and abrasive. The flycutter tends to pick up little particles of this as it crosses each patch of corrosion and they drag across the head and leave scratches in it. The only to get it perfect is by hand afterwards as I describe above. You can have the best machinery in the world but sometimes there is no substitute for a hand tool and a craftsman's hand and eye. Share this post Link to post Share on other sites
Mattsav 1 Posted January 20, 2006 Dave, Switch to a PCD (diamond) tip for corroded heads. They dont leave the tracking marks across corrosion as like carbide does. I can let you know the cheapest place I've found to buy them if you want. When that head is smoothed as dave says you'll probably see marks where the cutter has bounced after going over the chambers etc. Looks like it was machined with a blunt nail! We only ever have heads come back after skimming from one customer who insists on using the cheapest s*itty gaskets he can find! The other big issue we have is mechanics who take a DA sander to the head to clean it up. We have to machine more off the head where they have rounded off the edges around the chambers. They do more harm than good. Share this post Link to post Share on other sites
petert 586 Posted January 20, 2006 For the surface finish, an Ra of 1.6 (or N7) is classed as use for static mating surfaces? you should be able to do Ra0.8 with a carbide tip. You can do Ra3.2 with a 14" 2nd cut file! Share this post Link to post Share on other sites
PumaRacing 2 Posted January 20, 2006 Dave, Switch to a PCD (diamond) tip for corroded heads. They dont leave the tracking marks across corrosion as like carbide does. I can let you know the cheapest place I've found to buy them if you want. I was actually looking at PCD on the web the other day so I'd appreciate a source. When that head is smoothed as dave says you'll probably see marks where the cutter has bounced after going over the chambers etc. Looks like it was machined with a blunt nail! I think it was actually machined with a plough grinder not a flycutter. If you look carefully at the top pic you can see a repeating pattern about 5mm wide which is indicative of plough grinding wheels. Freshly dressed those do a fine job but this one may have needed a touch up. I don't think there'll be bounce marks though if this was a plough grinder. Share this post Link to post Share on other sites
SweetBadger 94 Posted January 20, 2006 (edited) No need to get it reskimmed and risk even more damage. Teach yourself some real engineering instead. Get a block of nicely flat wood (planed not just sawn) about 7" x 2.5" by an inch high and a couple of sheets of medium wet and dry paper. About 180 to 240 grit will do the job, and some paraffin. Wrap a sheet of w&d round the block and keeping it wet with paraffin work the head surface in random patterns making sure you cover all the area evenly. All you're really trying to do here is take maybe a quarter to half a thou off to improve the cutter marks so you won't destroy any flatness limits the gasket needs. What you should end up with is a lovely 'ground' sort of surface finish which is actually very smooth but not shiny. Just the ticket for modern gaskets actually. You've also made a tool and acquired a skill which you can use on heads and blocks in future to show up any low spots, remove the last bits of old gasket residue and save skimming costs most of the time if the surface is generally ok. Sometimes I have to skim really manky corroded heads and as you might know aluminium corrosion is aluminium oxide which is very hard and abrasive. The flycutter tends to pick up little particles of this as it crosses each patch of corrosion and they drag across the head and leave scratches in it. The only to get it perfect is by hand afterwards as I describe above. You can have the best machinery in the world but sometimes there is no substitute for a hand tool and a craftsman's hand and eye. Ok, thanks for the advice, i'll give that a go and post some pics of the end result... I still think I'm gonna get it checked out to make the surface is flat/true before I go to the effort of sanding it, and if I get a second opinion in writing showing that the work was sub-standard I may be able to get my money back for the skim at least! I'll probably quote matt's "Looks like its been machined with a blunt nail!" comment when I'm explaining how bad a job they've done... Edited January 20, 2006 by SweetBadger Share this post Link to post Share on other sites
PumaRacing 2 Posted January 20, 2006 Ok, thanks for the advice, i'll give that a go and post some pics of the end result... I still think I'm gonna get it checked out to make the surface is flat/true before I go to the effort of sanding it, and if I get a second opinion in writing showing that the work was sub-standard I may be able to get my money back for the skim at least! I'll probably quote matt's "Looks like its been machined with a blunt nail!" comment when I'm explaining how bad a job they've done... It really doesn't look anything like as bad as that to be honest. The patterning is possibly a function of the type of machine they use and if you can't feel the ridges by hand then all you need to do is as I've previously described. It's also extremely unlikely not to be flat whatever type of machine they did it on. Share this post Link to post Share on other sites
Hilgie 16 2 Cars Posted January 20, 2006 My head surface (flat): You head seems fixable with fine sandpaper like Dave says. Share this post Link to post Share on other sites
SweetBadger 94 Posted January 24, 2006 (edited) My head surface (flat): You head seems fixable with fine sandpaper like Dave says. Well I've got some vernier calipers on the case and the head measures 131.28 mm, so should be ok with a thicker head gasket... I've also had a go with some wet and dry and the face has come up preety smooth... Ended up using 400 grit paper in the end and it didn't take too long to get rid of the cutter marks. I could not get rid of all of the scratches/sanding marks no matter how much I tried, but the camera flash has made them appear much worse than they actually are. I finished it off with some fine wire wool which gave the surface a much more even matt finish and it now feels very smooth! So just got to clean the rest of it... Getting really fed up with cleaning caked on oil and grease, must have gone through about 5 cans of degreaser already! Edited January 24, 2006 by SweetBadger Share this post Link to post Share on other sites
returnofjim 0 Posted January 25, 2006 Ive had quite a few mi/pug heads skimmed and ive never seen one come back looking a bad as that! looks like a very poor job to me Share this post Link to post Share on other sites
petert 586 Posted January 26, 2006 Don't use a thicker head gasket. Mi16's respond really well to increases in CR. My favourite rebuild is 10.8:1, on Optimax without any dramas. Share this post Link to post Share on other sites
Ahl 4 Posted January 26, 2006 What about 11:1 peter? Too much? Share this post Link to post Share on other sites
Veero 1 Posted January 27, 2006 Eep, had me worried for a minute as I just had my Mi head skimmed for my rebuild and thought i could remember seeing machining marks but I dont think you can. Nothing much running a fingernail over it. Does this: look ok?? Veero Share this post Link to post Share on other sites
SweetBadger 94 Posted January 27, 2006 (edited) Eep, had me worried for a minute as I just had my Mi head skimmed for my rebuild and thought i could remember seeing machining marks but I dont think you can. Nothing much running a fingernail over it. Does this: look ok?? Veero Well, I'm no expert but it looks a damn site better than mine did, so I wouldn't worry... I suppose if you're in any doubt you could follow Dave's advice - worked for me! But if it looks and feels ok I wouldn't bother. Edited January 27, 2006 by SweetBadger Share this post Link to post Share on other sites
PumaRacing 2 Posted January 28, 2006 Well I've got some vernier calipers on the case and the head measures 131.28 mm, so should be ok with a thicker head gasket... I've also had a go with some wet and dry and the face has come up preety smooth... Ended up using 400 grit paper in the end and it didn't take too long to get rid of the cutter marks. I could not get rid of all of the scratches/sanding marks no matter how much I tried, but the camera flash has made them appear much worse than they actually are. I finished it off with some fine wire wool which gave the surface a much more even matt finish and it now feels very smooth! So just got to clean the rest of it... Getting really fed up with cleaning caked on oil and grease, must have gone through about 5 cans of degreaser already! You've done a fine job and hopefully learned something in the process. BTW the best thing for final finishing of aluminium surfaces is not wire wool but those green abrasive Scotchbrite sheets. Not sure where you buy them from because I nick mine from my mates work. Pan scourers do a similar job. Share this post Link to post Share on other sites
