rossman Posted October 23, 2008 Share Posted October 23, 2008 I am building an l24t engine with a p90 head. I want to notch the tops of the cylinders to clear the larger valves and hopefully improve flow a little. I am trying to figure out how to locate the valve notches/bevels on the cylinders so that they line up with the unshrouded valve cut-outs. I tried using just the head gasket but it didn't seem precise enough. Any body have a technique they would like to share? Thanks, Ross Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 23, 2008 Share Posted October 23, 2008 Put the dowels in the block and lay the headgasket on. Don't try to make it too precise. If you miss a bit you'll burn up the headgasket. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 23, 2008 Share Posted October 23, 2008 Clearance of the valves is literally a 'hit or miss' operation---some hit, some miss. As JM said, a positive dowelling gets the head properly registered...and in most cases the valves are free of the block at that point. Then 'unshrouding' becomes the main focus of the exercise. Leave enough near the fire ring for adequate sealing and most definately don't undercut it or as stated the head gasket will burn through in short order. Quote Link to comment Share on other sites More sharing options...
ozconnection Posted October 23, 2008 Share Posted October 23, 2008 Be aware that when you notch your block, you dont grind/file too far down the bore. Measure the distance from the top deck surface of the piston down to the top of the first compression ring land. When you have measured this distance, subtract a value of .040' or 1 mm (because of component stretching and flexing at high rpm's) and transfer this distance from the top of the cylinder down the bore and don't grind below this point or you might damage your top ring when you run finally the engine again. As for your unshrouding issue, you could use the locator dowels placed into the cylinder head. Get an L24 headgasket and lay it on your P90. If you can, push open your valves and see where they hang up on the gasket. If your careful, you can grind away the gasket until the valves open without tagging the gasket. A very slow process but it will work. Place the modified gasket onto your L24 block and you can now mark the block where the gasket doesn't completely cover the bores. This is what you need to grind. Oh, and dont forget to use your locator dowels in the block when your doing this...it needs to be accurate. Then, before you cut /grind your block, grab your L28 headgasket that you'll be using and see if it will be undercut anywhere. Like the boys already said, don't grind too wide or too deep. Cheers. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 23, 2008 Share Posted October 23, 2008 It should never touch the gasket. The deck of the engine possibly, but never the gasket. On an L20A...yeah. But in that case, you simply use an L24 Head Gasket of proper vintage (as me how I know that tidbit!) My compatriot is in Sydney currently, then on to Adelaide, and Olympic Dam... And I'm here in Nigeria shuffling flights for a follow on to someplace in the jungle 4 hours south of Jakarta... How did I get it this chicken outfit anyway? Oh yeah, they paid me... Quote Link to comment Share on other sites More sharing options...
ozconnection Posted October 23, 2008 Share Posted October 23, 2008 It should never touch the gasket. The deck of the engine possibly, but never the gasket. On an L20A...yeah. But in that case, you simply use an L24 Head Gasket of proper vintage (as me how I know that tidbit!) My compatriot is in Sydney currently, then on to Adelaide, and Olympic Dam... And I'm here in Nigeria shuffling flights for a follow on to someplace in the jungle 4 hours south of Jakarta... How did I get it this chicken outfit anyway? Oh yeah, they paid me... I'm not sure that I know what you mean. "Never touch the gasket"? The idea behind using a gasket that closely represents the block for which the head is to be used allows the user to see where there is contact between the valves on the head and block. You're expecting contact, that's why using the smaller L24 gasket is a great template for this sort of thing. I went into the garage just now to measure the diameter of the two valves in an N42 (I44mm/E35mm) and it was pretty much spot on 83mm's, the same as the L24 bore. I used an l24 gasket on an L20 once without any dramas whatsoever because I couldn't get an L20 HG. That's why I don't see any problem using an L28 gasket on an L24. Where is your collegue staying in Sydney Tony? PM me with some details if you like and I can ask him what you're like to work with! Quote Link to comment Share on other sites More sharing options...
rossman Posted October 23, 2008 Author Share Posted October 23, 2008 I'm being a little anal about this I guess. I just don't want to screw it up! I was trying to figure out how to locate the notches along the circumference of the cylinder. It looks like they should be slightly off center. I guess I will just sharpie mark the l28/p90 head gasket using the dowels in the head, then transfer the dowels/gasket to the block and eye-ball it from there. Unfortunately the used l24 head gasket that came off the engine is out of round. ozconnection - I think Tony D means that the notches should not touch the gasket when installed. You advice about the piston ring is right in line with "How to Modify..." Thanks for your help guys! Quote Link to comment Share on other sites More sharing options...
ozconnection Posted October 23, 2008 Share Posted October 23, 2008 I don't think that if the L24 HG isn't perfectly round it would make any difference to what you're trying to achieve. I wonder if someone you know can let you have an decent old L24 gasket to muck around with. Why don't you go out and see if you can buy an el-cheapo L24 gasket and play with that? "ozconnection - I think Tony D means that the notches should not touch the gasket when installed." Yes, that's good advice, I just wasn't sure if that's what he meant. Quote Link to comment Share on other sites More sharing options...
PalmettoZ Posted October 23, 2008 Share Posted October 23, 2008 It should never touch the gasket. The deck of the engine possibly, but never the gasket. On an L20A...yeah. But in that case, you simply use an L24 Head Gasket of proper vintage (as me how I know that tidbit!) My compatriot is in Sydney currently, then on to Adelaide, and Olympic Dam... And I'm here in Nigeria shuffling flights for a follow on to someplace in the jungle 4 hours south of Jakarta... How did I get it this chicken outfit anyway? Oh yeah, they paid me... Hey Tony D- Just curious, what do you do that takes you all over ? Your in Nigeria? Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 24, 2008 Share Posted October 24, 2008 Compressor Engineer for FS-Elliott. I'm sure my mate Elton and the VP of Marketing Sales (oh yeah, he's on a TOUGH assignment, right!?!?) are in the Land of Oz evaluating local shops for a distributorship licensing agreement. We don't have local representation there yet. Comp Air NZ would be a feather in our cap to snag away from Cameron, and being I know people working there it would be an easy excuse for me to go... But noooooo! Yes, I was referring to not modifying the head gasket. Up to, but never touching it. I personally prefer to use a previously compressed gasket as well, as it's more accurate of what you have in the engine instead of an undeformed one. And if you tag it with the stone...meh, no biggie! You should see the notches on our L20A bores to get the L28 Size valves to clear the bores! Muahahahahha! Quote Link to comment Share on other sites More sharing options...
madkaw Posted October 24, 2008 Share Posted October 24, 2008 Rossman, when I ever get my laptop back from the shop:mad: I post some pics of how my block (l24) was notched for my bigger valves on my early e-88 head. I don't have exact instructions on how too, but I know the machinist used the stock gasket as the reference to transfer marks. Good luck! I just remembered that I have the pics posted on CCZC. Just look up the photos under Madkaw. I have pics of both the head and the block if that will help you. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted October 24, 2008 Share Posted October 24, 2008 So........will P90 valves hit the bores of a virgin l24 block? Quote Link to comment Share on other sites More sharing options...
rossman Posted October 24, 2008 Author Share Posted October 24, 2008 Rossman,when I ever get my laptop back from the shop:mad: I post some pics of how my block (l24) was notched for my bigger valves on my early e-88 head. I don't have exact instructions on how too, but I know the machinist used the stock gasket as the reference to transfer marks. Good luck! I just remembered that I have the pics posted on CCZC. Just look up the photos under Madkaw. I have pics of both the head and the block if that will help you. Thanks for the pics! I am a visual guys so seeing that really helps. How long have you been running your engine with the notches? I will be running fairly high boost (14 - 15 psi) on cast .075 over pistons. I am a little worried about burning up the rings. Then again, if I trash the l24 I will have more incentive to rebuild my l28 turbo block Quote Link to comment Share on other sites More sharing options...
rossman Posted October 24, 2008 Author Share Posted October 24, 2008 So........will P90 valves hit the bores of a virgin l24 block? See Tony D's first post on this thread. It seems like a good idea to notch the cylinders anyway to help flow into the cylinders. Quote Link to comment Share on other sites More sharing options...
madkaw Posted October 25, 2008 Share Posted October 25, 2008 Sorry, can't give any reports of the engine running since I haven't started it yet. The car is apart for paint and I didn't want to assemble it just to start the motor. Most of the things done on this motor are right out of "how to modify your datsun engine" book. The bigger valves will not clear the block so you need to clearance the side of the bores , plus give room for breathing. I put the biggest valves I could fit in the head which brought my chamber size down to about 41.5, so the clearances will also help reduce compression by reducing the chamber size slightly. If you saw the head chambers I also unshrouded as much as I could. Basically you are notching the bore like they did on the l26 with the bigger valves. It should run strong--if I ever get this thing done. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted October 27, 2008 Share Posted October 27, 2008 I don't like notching the cylinders because this can focus pressure directly onto the top of the ringland rather than have the piston in the way to take said pressure. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 27, 2008 Share Posted October 27, 2008 I don't like notching the cylinders because this can focus pressure directly onto the top of the ringland rather than have the piston in the way to take said pressure. There are guidelines to prevent issues with the pistons and rings. The How to Modify book suggests that you don't get closer than .040" from the top of the ring. When I did my L28 I only went about 2/3rds of the way from the deck to the first ring, but the notches are a lot shallower on an L28. Quote Link to comment Share on other sites More sharing options...
Phred Posted November 1, 2008 Share Posted November 1, 2008 Sometimes it doesn't take too much grinding. Phred Quote Link to comment Share on other sites More sharing options...
rossman Posted November 2, 2008 Author Share Posted November 2, 2008 Well, bad news. I started cleaning up the old gasket material and noticed that one of PO's had scratched up the deck pretty badly. The deck needs to be resurfaced. I'm guessing this can only be done by disassembling the bottom end. I may just go ahead and rebuild my f54...which also needs to be resurfaced. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 3, 2008 Share Posted November 3, 2008 What are we talking here, like scores or just scratches? Something a light stoning would clear up? Photos would be good in this instance. Even Celphone photos! LOL Quote Link to comment Share on other sites More sharing options...
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