rebuilding HELP 390?
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rebuilding HELP 390?
i am rebuilding an engine out of my 76 ford pick-up . I am having problems getting my pistons back in .. when i put # 1 and #5 piston in I cannot turn the crank .... i have found that someone has rebuilt this before. it has been bored 30 over and the crankshaft 10 under on the crank barings and 30 under on the rod ... this is my first time rebuilding a engine ...before i took the pistons out i #ed them 1-8 so they should go back in someone please HELP
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Did you mark them on the outside edge cap and rod ? Your sure your not changing them side to side, 5 on 1's side and one on 5's as I believe the rods are offset so the insert won't ride the radius of the crank journal. kotzy
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From what I gather is you still have the problem. If you install one piston can you turn it? Sounds to me like you may have been furnished the wrong set of rings if they go in the bores tight. Did you check the end gap on the rings? A compression ring pushed squarely into the bore should have .003 to 004 thousands end gap per inch of cylinder or in the case of a 4" bore .012 to .016 thousands. That is not the whole story however, if the pistons grooves were machined for low tension rings the grooves are not as deep and the old style rings which are thicker in depth will drag like the devil. This is felt on assembly once all the rings of a piston are in the bore you should be able to push the pistons down, not have to beat them in. Perhaps this will help. kotzy
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I did check the ring gap and it was perfect however i looked over my old rod barrings and i could barely make it out but in ink if had .020 not the .030 that i was told. so all i need to do is order the right barrings and it should all be good
Tuned
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From: Oregon
Yeah, if you had .030 bearings on a .020 journal, it'll bind up.
You didn't mention if you had any of the other rods installed yet. If the other rods are in, and it just binds on #1 & #5, there might be a side clearance issue.
Some crank grinders like to leave a big radius on the edge of the rod journals. If the bearings aren't chamfered to clear the radius, it'll bind up. Also, the rods bores aren't truly round until the caps are torqued. A lot of people have tried turning an engine over before tightening the main or rod caps down, and had it jam up.
You didn't mention if you had any of the other rods installed yet. If the other rods are in, and it just binds on #1 & #5, there might be a side clearance issue.
Some crank grinders like to leave a big radius on the edge of the rod journals. If the bearings aren't chamfered to clear the radius, it'll bind up. Also, the rods bores aren't truly round until the caps are torqued. A lot of people have tried turning an engine over before tightening the main or rod caps down, and had it jam up.
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thank you for that info... i replaced the barrings with .020 and every thing turns smooth now . i have about 85% of the engine done .. the only thing I 'm not sure of is installing the push rods .. I have only worked on ohc on my honda ...
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From: Littleton, CO
You need to have your intake on before installing the pushrods. They just drop right in, fit in the lifter cup and up under the cups under your non-adjustable rockers (and shafts)...
--Mike
--Mike
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First did the crank spin feely without the pistons in? I will assume so. Secondly you are using a engine assembly lube on all parts pistons, cylinders, rings, and bearings. Motor oil does not "stick" to parts during assembly. Did you plastiguage or use a caliper to check all the bearing oil clearences. If the oil clearence is too small it will cause binding as well as a lack of lubrication. Lastly someone may have put the rods on the pistons wrong. Check the side of each rod end it will have one side completly smooth and flat( this side goes towards the other rod they rub together) The other side should have a indent in it to ride on the radius of the crank journal, it should face a crank counterweight. The rods can be interchanged in the cylinders if this is the case, just make sure the dot or arrow on the piston faces the front of the engine and the rod corresponds with the above guidelines.
Last edited by blue350; Dec 1, 2007 at 10:59 AM. Reason: Found problem
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