madkaw Posted November 21, 2005 Share Posted November 21, 2005 I've been searching but can't seem to find a definitive answer.I am beefing up my 240 motor and am wondering about notching my block. I have put the 280 valves in my e-88 head with a stage 2 cam and my pistons are .40 over. Do I still need to allow for relief in the cylinders. I thought I read that if you go atleast 10 over on pistons your okay but I can't find similiar info. Anyone steer me in the right direction. thanks steve Quote Link to comment Share on other sites More sharing options...
z-ya Posted November 21, 2005 Share Posted November 21, 2005 I would think that you could take some simple measurements and determine if you need to machine notches. If the block is not assembled, you can rest the head on it (with the locating dowels in place) and turn the camshaft slowly with a wrench on the cam sprocket. If the head lifts up, you need to notch the block. You can also put a couple of head bolts in (don't tighten them down) to keep the head from moving while you are turning the cam. The amount of lift you have will also dictate how far the valves go into the bore. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 21, 2005 Share Posted November 21, 2005 You have to consider how the valve is going to breathe when it is jammed right up next to the cylinder wall too. Even when the valve is fully open the cylinder wall is going to be right there. I would think that a smaller valve might actually breathe better than the larger valve unless you notched the block. What I'd suggest is that you lay the headgasket on the block and see how much you can take away before you get to the fire ring. I haven't done a L24, so I don't know how its going to turn out. If you can take a good amount out, like 1/16" or more then do it. If not, then it probably isn't worth the hassle. I'd also unshroud the valves in the head as well. If the chamber is the same size as the bore and both are opened up then you'll give the airflow a smooth path around the open valve. That's what you're shooting for. Quote Link to comment Share on other sites More sharing options...
madkaw Posted November 21, 2005 Author Share Posted November 21, 2005 I have unshrouded the chambers, thanks. I brought this up to my machinist to look at and I appreciate all the advice. Sounds like the definitive answer is to plop the head on there and make sure nothing hits and then see the advantages of possibly notching. I think I must of read about this in my "How to Modify" your datsun book which the machinist has right now . Quote Link to comment Share on other sites More sharing options...
zcarnut Posted November 21, 2005 Share Posted November 21, 2005 If you discover that the block needs to be notched for valve clearance just make sure that the notch is not deep enough to uncover (expose) the top piston ring on the piston. This will result in top ring failure. You should be OK, but if you have a high lift cam and a milled head you might be too close for comfort. Quote Link to comment Share on other sites More sharing options...
madkaw Posted November 21, 2005 Author Share Posted November 21, 2005 Anybody have a pic of the notching. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 21, 2005 Share Posted November 21, 2005 Found a pic online. There is a pic of the block being honed and you can see it there. http://chevyhiperformance.com/techarticles/46778/ Also the How to Modify Your Nissan/Datsun OHC Engine book has a pic (and even a pic of a block that wasn't notched enough and the valve head hit the block). Quote Link to comment Share on other sites More sharing options...
madkaw Posted November 21, 2005 Author Share Posted November 21, 2005 Thanks Jon for the pic, that helps me picture in my head the whole notch process. I would think that my machinist has been down this road before but he is not familiar with these older Nissan engines. Since this isn't a stock rebuild i am trying to cover all the basis with him so we do it right the first time. Thank God there is some great sites and help from you guys. I thought (my memory sucks)that when I checked the original valve sizes that my head had the larger ex valves but smaller in. valves(165). The head was off of a late model 71.So I guess what i am babbling for is I thought the interference would be the intake side Quote Link to comment Share on other sites More sharing options...
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