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L-28 Flat top- MN47 build


madkaw

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Putting this combo together and will document the fun. I bought a 1983 zx motor about a year ago with plans to put my E88 on the short block. I sold off the P79 head since I didn't have plans to use it.

I only paid 200$ for the motor and got 150$ for the head, so not too bad a start!

The engine had 110K miles on it and the internals looked good. Maybe someone can verify for me that the stock p79 pistons do indeed have P79 stamped on them like these. The main bearing caps also had dots numbered in them-factory? The bores were so smooth it could have been touched before but all measure within stock limits. a cleaning and ball hone was it needed to be useable!

The crank end could look better, but at worst a speedy sleeve could cover the groove and rust. Pistons measure above deck as archived at 19 thou. The pistons themselves look new after cleaning.

I plan doing a minimal, frugal- rebuild, bearings and piston rings. We know all the Nissan stuff is good.

 

The head will be a Maxima 47. I have always be intrigued by readings in the archives by 1fastZ and others about this head. It might be the best band for buck for our motors, if it can be done right. Yes the CR will be high, but thats the fun right?  I'm hoping the versitility of my MS3 will help me manage and control the high CR motor. Not sure if i will be going straight to FI with this build or using the Mikuni's first. I have an early FI intake on the way now since I sold off my 83 intake for 75$.

 

I found a n47 on the innerweb and had it bought and shipped for 150$ Took it to the machine shop to find it was .030 out of flat-not good. It did come complete with cam and rockers which i think are very useable. They did refund my money and I kept the head.  have another on the way 

 

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  • 2 weeks later...

When you put it back together, set the rear main seal so that it doesn't ride in the groove in the crank. I would say it was rebuilt at one point due to the punch marks on the main caps. Those are Nissan OEM pistons (P79). Check all the piston sizes are the same. I remember one engine I rebuilt had one oversized piston in it. Probably a dealer repair as it was an OEM piston. Not sure what the combustion chamber volume is on an MN47, but your CR might be too high.

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CR should be 10.65 based on 39cc chambers.

Got another mn47 that wasn't warped, just rusted and a bent valve :0

At the machine shop getting a valve job and surfaced. Sticking with stock valve size for now and will dyno . I might unshroud the exhaust side a little, it's really tight.

 

Plan on swapping all parts from warped head to rusty head= 1 good head job!

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