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17 Mar 2013, 11:47 (Ref:3219966) | #1 | ||
Racer
Join Date: Mar 2009
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Sort of griffith but more Ford v8 engine related
Hi Guys.
Boxing up my Small block. Spec is quite mild, 302 block 68 hipo heads, 270 cam etc etc. In the past and before my time the heads have been converted to screw in studs and run moly pushrods with comp cams roller tip rockers.. The heads have a large hole where the pushrods run down to the lifters... some earlier hipo heads have a smaller slot with the possibility of less sideward movement for the pushrod! The engine to my knowledge has never had guide plates but do I need them?? The plates themselves are cheap enough but not sure if my engine has had them in the past and is missing them or whether They have never been fitted.. When the valves are adjusted I am conscious that you can move the rocker off the tip of the valve due to the large clearance hole in the head allowing the pushrod to move a lot more relative to the rocker..Obviously this will not be a problem when the lifters have pumped up etc but I am worried about needing the extra insurance in the event of missing a gear, bouncing a valve etc!! The trouble is that I am unsure whether I can just fit them and there will be enough thread left to take up the thickness on my existing ARP screw in posts, whether I will have to mill down the bosses in the head to allow for the thickness of the plate, or whether they have been fitted in the past and I can just re-fit.. Other option I suppose is to buy new posts which are compatable with the proposed guide plates.. The engine spec is relatively mild so I guess the other question is Do I need them?? or am I just worrying un-necessarily. I suppose I could just buy a set and fit and see whether anything fouls at full lift!! Other option is that if anyone currently has their engine in bits could they measure their existing rocker mounting boss on their heads to give me an indication..Trouble I have is that I don't know if mine have been previously machined or are std! Any good Ford small block fettlers out there with some prior knowledge Cheers Neil Last edited by Heightswitch; 17 Mar 2013 at 12:13. |
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17 Mar 2013, 12:22 (Ref:3219975) | #2 | ||
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Join Date: Sep 2006
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For the cost involved,why not fit the plates anyway? Depending on the cam you may have to fettle a little out to give the push rods clearance. These engines can be run without them,but is the risk worth it.
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17 Mar 2013, 19:53 (Ref:3220188) | #3 | ||
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Chevy man here but have built Ford V8's as well and the theory is the same. I always use the guide plates with those type of large slot heads but I am always running full roller rockers and followers also you really should use hardened pushrods as well which you are. I am sure there will be enough length in the screw in studs but another concideration and the reason they may have been left out is the rocker geometry as it will alter when you fit the plates and may require a new set of longer pushrods. BTW I have built an engine once and fitted the guide plates on some early camel hump heads with the small slot and they bound so I had to drop the guide plates.
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17 Mar 2013, 20:17 (Ref:3220202) | #4 | ||
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Been doing a bit more reading up and I think I am right in this....
The roller rockers are rail type designed to work with long stem valves..Comp cams don't recommend using guide plates with these rockers in case they conflict with each other... If I had flat roller tip rockers then I should use guide plates... Looks like it will be OK as is with the mild cam it has.. Recommendation to go for guide plates if the spec of the engine was any wilder..IE much higher lift cam...That would also mean new roller rockers. What I don't know is whether the bosses on the heads were milled down to suit guide plates or just tapped for screw in studs..I need to find some std heads to compare. It all seemed to work pretty well when I was last out (apart from the oil pick up issues that is) so I am probably just being a bit OTT. Guide plates are definitely a better bet for added insurance but with a max 6000 rpm motor and a 270 degree hydraulic cam I reckon I should be OK for now.... Famous last words.. N. |
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17 Mar 2013, 21:22 (Ref:3220233) | #5 | ||
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The bosses would generally be milled down when they are theaded at least everyone new or 2nd hand I have seen are as I doubt the screw in stud would sit there correctly if they wernt.
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17 Mar 2013, 21:38 (Ref:3220241) | #6 | ||
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Al is quite right about the rocker geometry and ideally the rockers should sit slightly down towards the pushrods otherwise you will not get full lift regardless of what cam you use.
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17 Mar 2013, 22:15 (Ref:3220258) | #7 | ||
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Now that I have identified all the bits the engine was built with I am generally happy that It is all as it should be...Time to get it boxed up and back in the car.
The bosses are a machined finish..Would be interesting to compare measurements with an un modified head to see how much material has been removed .... Just a new oil pump to go back in now..Didn't like the look of the one I removed.. N. |
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