Sparky Posted August 18, 2009 Share Posted August 18, 2009 Hello everyone, So I bought a new (to me) car with a "Rebuilt" engine only to find that the high compression pistons hit the cylinder head. The head has been removed and the offending bit marked as seen below: So as you can see the dome in the piston hits the head ever so slightly, it's not so bad that the engine cannot be turned over by hand but there is a noticeable resistance when doing so. Others with a similar problem resolve the issue by reshaping the chamber like so: But I think that that might be a bit aggressive and that a more thoughtful approach to combustion may yield better results. By reshaping the chamber to promote or entice a controlled flame spread and in keeping with the somewhat "hemispherical" nature of this head like so (red line is material removal, blue line is slightly repositioned ridge) Am I just talking nonsense here? I'm imagining that as the intake charge ignites it travels away from the spark plug aided by the angle of the plug and the existing ridge and "swirls" counter clockwise to the exhaust valve. By aggressively reshaping or removing this ridge as shown in the second picture you begin to lose the benifit of having it, by reshaping to keep as much of that ridge as possible I can only hope to maintain the entent of the original design. Obviously i'm not experienced in this field of expertise and so I ask the experts here for opinion on both my approach, and for advice on how to achieve my goals, IE best tools for the job (grits, drums, cones, process) and wether or not post process check up..aka CC'ing is an absolute necessity. I'm not after peak performance, I just want to get the car running and driving in a reliable enough state so that It can take over for my current daily driver. Pictures of the aforementioned car will come shortly, in the mean time I'm hoping to get a good foundation of advice so that I may proceed before weeks end. Thanks. Quote Link to comment Share on other sites More sharing options...
doublexl240z Posted August 19, 2009 Share Posted August 19, 2009 amazon. com has a book " How to modify your Nissan and Datsun OHC engine" has all the info you will need!! Under 20 bucks if I remember correctly. Quote Link to comment Share on other sites More sharing options...
naviathan Posted August 19, 2009 Share Posted August 19, 2009 Lets see the pistons as well. Can't decide on flow with only half the picture. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted August 19, 2009 Administrators Share Posted August 19, 2009 ... Others with a similar problem resolve the issue by reshaping the chamber like so: ... Thanks. That mod is the route I would take. amazon. com has a book " How to modify your Nissan and Datsun OHC engine" has all the info you will need!! Under 20 bucks if I remember correctly. You might take a look at the pictures again... NOT a Datsun cylinder head, i.e. that book would do him NO good here! Quote Link to comment Share on other sites More sharing options...
MAG58 Posted August 19, 2009 Share Posted August 19, 2009 Ew. It's german. Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted August 19, 2009 Share Posted August 19, 2009 Ew. It's german. Not worth the time spent working on it, right? Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted August 19, 2009 Administrators Share Posted August 19, 2009 (edited) Not worth the time spent working on it, right? My BMW Piston-to-combustion chamber clearance issues were 100% resolved by installing an "additional" cylinder head! http://forums.hybridz.org/showthread.php?t=150253 Edited August 19, 2009 by BRAAP Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted August 19, 2009 Share Posted August 19, 2009 Hey now, we can't all have our cake [///M3] and eat it too [LSX] Quote Link to comment Share on other sites More sharing options...
Sparky Posted August 20, 2009 Author Share Posted August 20, 2009 Thanks everyone, bought a new cable for my rotary tool now all I need is the sanding drums... The pistons: http://forums.hybridz.org/picture.php?albumid=3&pictureid=1362 How imperative is it that I CC the heads after the fact? And as far as the Ew...it's german comment, you should see the car! Talk about nasty: That's all I'm willing to show of this beast until it runs and drives Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted August 20, 2009 Share Posted August 20, 2009 And as far as the Ew...it's german comment, you should see the car! Talk about nasty: That ol' boy is modifying a Merc straight six head to fit on the datto L28 block http://forums.hybridz.org/showthread.php?t=150479&highlight=M104 Quote Link to comment Share on other sites More sharing options...
MAG58 Posted August 20, 2009 Share Posted August 20, 2009 Thanks everyone, bought a new cable for my rotary tool now all I need is the sanding drums... The pistons: http://forums.hybridz.org/picture.php?albumid=3&pictureid=1362 How imperative is it that I CC the heads after the fact? I see your problem. It appears someone has bolted a grand piano on the top of your german pistons. And Yes. CC them to make sure they're all the same. Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted August 21, 2009 Share Posted August 21, 2009 Is that earlyer pistons in a late modle head? i would try to kkep the clearence as tight as possable to enhance squish. Douglas Quote Link to comment Share on other sites More sharing options...
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