KA24E rebuild

[crs240sx]

I have an extra motor with a toasted bottom end but the top is fine. I figured since my race motor is a bone-yard piece it may be wise to rebuild at least the head of my spare motor. It will also let me get more comfortable with it since I have never rebuilt a motor before.

Can anyone help me with the folowing questions:

What can I do, legally, to improve performance? I know I can port match the exaust and plain the head. Not sure how much I can take off the head though. I plan on running the early higher compression pistons at some point.

What should I do at a bare minumum to freshen this piece up? What parts should always be replaced? Timing chain and guide, valve seals, etc?

I have a FSM and access to proper tools for measuring everything once I have it disassembled.

Thanks,
Corey

[joeg]

Clean it; bore/hone; deck the block a few thou; balance the crank, rods and pistons, match port; valve job; bronze guides; new springs, all new gaskets, rings and seals, chains, tensioners, etc.

Have fun!

[Geo]

Originally posted by crs240sx:
I figured since my race motor is a bone-yard piece it may be wise to rebuild at least the head of my spare motor. It will also let me get more comfortable with it since I have never rebuilt a motor before.

Don't sweat it. Rebuilding an engine is not that big a deal. The FSM is your friend. It will tell you everything you need to know. Others will be doing the hard part (machining and balancing).

Originally posted by crs240sx:
What can I do, legally, to improve performance? I know I can port match the exaust and plain the head. Not sure how much I can take off the head though. I plan on running the early higher compression pistons at some point.

For sure you want to balance it. I don't know the KA24 well enough to know if there were other differences besides just the pistons. If there were, be careful. The rules specifically state that whole components must be changed and you can't just pick the best parts. If the only difference is the pistons, have at it.

Definitely port match. Get a really really good valve job. Remember that the angles must conform to the stock spec, but the stock spec has tolerances so you have some room to play with. IIRC the seat can be blended in with the port.

The FSM should spec a minimum thickness of the head. That will tell you the legal limit of how much you can cut it. Just be sure you don't increase your compression too much as a result.

Originally posted by crs240sx:
What should I do at a bare minumum to freshen this piece up? What parts should always be replaced? Timing chain and guide, valve seals, etc?

If the KA chain is anything like the SR chain, it's pretty stout. However, it's relatively cheap enough that unless the chain is pretty new, I'd replace it. If the KA is like the SR, you should always replace the guides when you replace the chain. Replace all seals of course. I'd replace all bearings and rings as well.


------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[ITA240]

Corey,
Pretty simple really. MIght suggest having the rods checked for straightness and magnafluxed. I have seen several break rods. Get a GOOD shop to set up the head. It is worthwhile. email me with any questions, I might be able to help.

Jim
ita #23

[email protected]

[crs240sx]

I'm just going to work on the top end for now since I have a spare head. I didn't know I was allowed to work on the valve seat. guess I'll have to go back and read that part again.

As far as specific questions, can anyone tell me how much I should tell the machine shop to take off the head. Or what the max compression ratio is and what it is with the stock early pistons. Then maybe the machine shop can help me out.


What else do I need to get the machine shop to do? On the head-only.

Thanks
Corey

[joeg]

All you want on a head shave is a minimum "truing-up" cut. This assures a flat surface (which is why I always recommend a block "decking")for sealing purposes.

Big cuts increase compression but require some re-phasing work on the cam's timing (offset keyways and the like). Accordingly, try not to go overboard on head milling (or block-decking for that matter).

Cheers.

[erlrich]

Originally posted by crs240sx:

As far as specific questions, can anyone tell me how much I should tell the machine shop to take off the head. Or what the max compression ratio is and what it is with the stock early pistons. Then maybe the machine shop can help me out.

What else do I need to get the machine shop to do? On the head-only.

Corey - there is a minimum head thickness listed in your FSM, but you really don't want to take that much off the head unless you are doing a complete rebuild, including balancing/blueprinting. As George and joeg have already pointed out there are other issues that come into play with taking that much material off the head, including piston to valve clearance, cam timing, and staying under the max compression ratio. I would stick with just 'cleaning up' the head if you're only doing the top end. This also gives you material to take off in the future, when you do get around to doing that full rebuild. A good valve job from a reputable shop (preferably one that does racing engines), including new springs, guides, and seals, should take care of the head.

You also stated in your original post that "I know I can port match the exhaust" - don't forget the intake side too, as you have much more to gain there than on the exhaust side. Just remember you can only go 1" into the manifold.

The compression limit on the '89-'90 ITA 240SX is 9.5:1 (2002 GCR). The early '89 engines came with flat-top pistons that are listed as having a 9.1:1 compression ratio, while the later engines came with dished pistons and were listed as 8.6:1. One thing to remember though, if you are planning on pushing the limit on the compression it will be up to you to calculate the actual compression ratio of your engine.

Earl

------------------
* ITA 240SX in process *

[This message has been edited by erlrich (edited January 15, 2003).]

[crs240sx]

Thanks for the helpful suggestions.
I'll dissemble what I have and send it to the machince shop and see whay they say.

[Engloid]

some of you suggested milling the head, and even decking the block.

Im interested in your views as to how this will effect valve timing, as it definitely does.

[crs240sx]

Just got the head back from the machine shop. They did a valve job and replaced the seals, tested the springs and presure tested the head. They did not take anything off the head as they said it was nice and straight. Is this ok?

Any advice before I re-aasemble? I will not actually be putting it back on the car until it warms up outside.

Anyone have a good link to a DIY port matching article?


Thanks for the advice so far,
Corey