Piston and Rod Question
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Piston and Rod Question
Im in the process of rebuilding my 1976 inline six and when we opened up my kit the pistons are a little different they have a little cup in the top of the pistion and its off to one side and I believe here is a little notch in one side, We were wondering what direction does it go on the engine? Also with the rod we noticed they have a little notch on one side and have the same question about that? I know I know I should of made sure of the direction but I got excited about the rebuild!!!Thanks for the help everyone
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the cups in the pistons should go under where the valves are when the head is on the block. the notches on the rods should go towards the front of the engine. Somebody correct me if I'm wrong here, I know that's how it is on a 60 Series.
Last edited by RotGrubestier44; Jun 2, 2006 at 05:26 PM.
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The 300 uses offset pins in the pistons, the notches need to point forward so they're all offset to the same [and correct] side. Same with the rods, notch faces the front of the block.
Many older 300's had flat top pistons, newer ones had an offset circular or "D" shaped recess. The flat tops had a shorter compression height leaving a larger gap between the piston top and the head. Newer designs raised the top of the piston [about .020"] and put in a recess to get the proper compression ratio. Advantage of the newer type pistons is better quench and from that more resistance to knocking.
If you're not having the block bored, before installing the new pistons in an older block you MUST use a ridge reamer to clean up the top of each cylinder. Over time a very slight ridge builds up in the cylinder at the top of the piston's throw. This needs to be removed so you don't score the piston skirts on installation. It's even more important when installing new pistons with a taller compression height because the top of the new [taller] pistons would wear against the ridge.
Many older 300's had flat top pistons, newer ones had an offset circular or "D" shaped recess. The flat tops had a shorter compression height leaving a larger gap between the piston top and the head. Newer designs raised the top of the piston [about .020"] and put in a recess to get the proper compression ratio. Advantage of the newer type pistons is better quench and from that more resistance to knocking.
If you're not having the block bored, before installing the new pistons in an older block you MUST use a ridge reamer to clean up the top of each cylinder. Over time a very slight ridge builds up in the cylinder at the top of the piston's throw. This needs to be removed so you don't score the piston skirts on installation. It's even more important when installing new pistons with a taller compression height because the top of the new [taller] pistons would wear against the ridge.
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Yea I seen the ridge you were talking about I will have that done. I also need to get the cam bearings installed. So then new pistons will have more compression?? or less? Ok so the notch on the piston goes forward and the notch on the rod goes to the cam side?????I was wondering mainly abouth the rod cause if it were backwards I would think that little notch would hit something. Thanks
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Find a good machine shop and for about $50 they'll hone the cylinders and take care of the ridges. Alternately, if you have Autozone stores in your area you can "borrow" a ridge reamer and cylinder hone to DIY. Shops usually charge about $25 to install the cam bearings, that's better than spending $100 on the tool required to do it yourself.
Acording to my Chilton book, most 1975- 78 300's had an 8.0:1 CR, only exception being the '76 and '78 E100/F100 models which "should" have been 8.9:1 CR. Your new pistons are probably going to give you an 8.5:1 CR, but hard to tell without knowing the exact model # of the pistons. There are dozens of pistons made for the 300's with CR's ranging from 7.8 up to 8.8, with 8:5 being the most common. I just spent two+ weeks deciding which pistons to use for my rebuild, so if you can give the piston brand/model I've probably got the specs for them.
Acording to my Chilton book, most 1975- 78 300's had an 8.0:1 CR, only exception being the '76 and '78 E100/F100 models which "should" have been 8.9:1 CR. Your new pistons are probably going to give you an 8.5:1 CR, but hard to tell without knowing the exact model # of the pistons. There are dozens of pistons made for the 300's with CR's ranging from 7.8 up to 8.8, with 8:5 being the most common. I just spent two+ weeks deciding which pistons to use for my rebuild, so if you can give the piston brand/model I've probably got the specs for them.
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Here is the info I got off the box that the pistons came in. I bought my engine kit through Northern Parts.
There Sealed Power
Skirt size 3.99875 +/- 0.00025
H519P
2.47 From top of Head
I dont know if those are the numbers and all you needed to find my CR if not Ill go look again.
There Sealed Power
Skirt size 3.99875 +/- 0.00025
H519P
2.47 From top of Head
I dont know if those are the numbers and all you needed to find my CR if not Ill go look again.
