'71 429 cobra jet engine rebuild...

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'71 429 cobra jet engine rebuild...

Post  Pastel Blue on June 28th 2016, 3:24 pm

This 4UA crank was turned once previously, looks like -0.10, Unfortunately, the engine was since used to the point of creating additional damage to a number of the bearings with this crank journal being the worst. How much can they turn a crank moving forward and is there bearings available to salvage this crank. I am not an expert in these areas, just trying to get some info before I approach a machine shop to do the work. The engine will need new bearings throughout. Cam shaft/lifters are original (to be replaced) and so are the cam bearings (to be replaced), all crank bearings will need replacing, as well as all rod bearings (+ some of the original CJ rods were changed out previously for the standard fare (a mix mash of rods...), so will I look to buy complete new rods moving forward? The pistons are TRW 0.40 overbore, not sure if they are salvageable (and when considering the desired compression ratio moving forward if I would even want to reuse these...) as well as the piston bores. There was no ridge in the bores, no obvious signs of damage, but some slight wear in the piston skirt path within the bore. The pistons came out easily. How do I know if the bores can do with a honing or a re-boring? Don't really want to re-bore if it can be avoided...

Trying to figure out what I need to check that I can do at home, whether there is a rebuild kit available based on the info provided here and where to go with this moving forward. I know at the end of the day, everything will wind up at the machine shop, just would like to be somewhat informed when I start to talk to them about what I want done. I have never built an engine myself, enjoyed tearing this one down, kept everything organized, but it appears most parts will have to be replaced anyways, due to wear and tear. Again, I am looking to keep the engine reasonably original, and running on pump gas. The heads look to be in good shape, will have them gone through as well. Confusion reigns supreme when it comes to what I should do to run pump gas in the future. We have 93 octane with 10% ethanol available here. Compression ratio I should strive for and how to achieve with the rebuild? You get my drift, just a guy re-doing his rare 'stang and trying to do it right with some insight in what needs to be done. I can post more pictures if required. Thanks.

See additional phots in my second post on this...






Pastel Blue

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Re: '71 429 cobra jet engine rebuild...

Post  Paul Kane on June 28th 2016, 3:39 pm

Pastel Blue wrote:This 4UA crank was turned once previously, looks like -0.10, ..the engine was since used to the point of creating additional damage to a number of the bearings... How much can they turn a crank moving forward and is there bearings available to salvage this crank. ...all crank bearings will need replacing, as well as all rod bearings...Thanks.
Both rod and main bearings are available for these engines all the way down to 0.060" undersize. The OEM cranks can be fine to use to 1000 hp turned down that far (the OEM rods are not good to that power level).

Mahle purchased Clevite and killed the SCJ full-groove main bearing but you can find mains in 1/2-groove down to 0.060" and 3/4-groove in undersizes down to at least 0.020" (I have 3/4-groove in 0.030" if needed).
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