1973 Rebuild

[madkaw]

Are you machining the piston reliefs or do they come that way?


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[Takhli]

Hi, Madkaw.

The rods are Datsun units, 133.0mm center-to-center, used in the early 240's, where as the 280s use 130.35mm. Anyway, the extra length provides a better stroke to pistion diameter ratio because there is less side thrust. As for the pistions, they came from J&E without the sparkplug boss relief in the dome. We had to lay the piston against the head to identify clearance issues. We could have taken a clay mold of the chamber and sent it into J&E but that would have driven the price of each piston much higher. As it is, they were $105.00 each. 

[madkaw]

Gotcha- 240 rods
Power band your shooting for ?
Couldn't talk MATT into some more CR!!



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[Takhli]

Max RPM around 6500; want a car he can drive anywhere without gasoline issues and pinging.

 

[Takhli]

Also, don't want to have issues with cam height. The deck is 0.003-inch lower already. When we surface the head to get our target chamber volume we will also need to surface the top of the head to make certain all the mating surfaces and cam towers are square with each another, so we're probably looking at more than 0.030-inch of metal removal. If we go with heavier surface cut to raise the compression we were looking at the possibility of swaping the vavles - an un-needed expense for a car that won't see track time.

[madkaw]

Chamber size you are shooting for?


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[Matthew Abate]

Chamber size you are shooting for?


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About 55ccs


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[Zed Head]

1 hour ago, madkaw said:

Chamber size you are shooting for?

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He gave details in #395.  Phones...

Still fascinated by the piston design, with the ridges and the thin top ring land.  Detonation is a big problem with these engines.

Have you (Takhli) built many L series engines or are you breaking new ground here?  Just curious. 

[Takhli]

Piston design was a surprise to me as well. Very interesting concept that J&E used. Don't know if other pistion builders are following suit or why they chose to employ the design on Matt's pistons; we simply took down the numbers and told J&E the compression ratio we were looking for. Hell,... for all I know we could be an experiment! But according to our machinist the ridges help eliminate "Black Wall"; that's a term I never heard prior to two weeks ago and haven't investigated. But, I think it is a varnish of fuel and oil caused by too much heat at the top of the cylinder, that can extend down into the ring area to screw up the ring seal.

As far as my experience goes, I've built engines since high-school - professionally as an employee and for my personal and friends use. That includes experimental development of drone engines and a cylinder head teardown on an L24, years ago, but mostly I'm a pushrod engine builder and this is my first L-series rebuild. Different OHC engines each have a pequliarity and their assembly and modification need to be well thought out. Research and investigation are the keys as well as measured self confidence. My method is to ask the right people the questions I have, get second oppinions and read everything I can get my hands on. 

[madkaw]

Interesting choice of forged pistons for a relatively modest build.


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[Takhli]

Like I said; we had to go with custom pistons because we're using the longer, early production L24 rods.

[madkaw]

Gotcha


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