Valve Job

[bzdel2441]

I did a port and polish job on a used head that I got (had been worked on in the past)...How do I know if I need a valve job or not??? It is not an all motor jeep... just an renix with a new cam, HO head, and misc bolt ons....

Thanks
Chris

Oh Yeh.... If I need one does anyone know about what it would cost me??

 

[John(XJ)Jeep]

Actually nice of you to ask this question I don't have to make a thread. :wave:

Today I'm yanking off a HO head from a sport at the junkyard and I was wondering if I'm gonna need that too. Don't know exactly yet the condition of the valve train but by looking through oil filler cap I've noticed it's pretty gunky in there. Havin't pulled the head or the cover yet cause my buddy that works there has FAT tools and couldn't get it off yet. :laugh3:

Also I'd like to know it'll work on my 88' XJ? I don't know exactly for sure but theoretically it should be ok. And another thing, is it possible to have an MPI engine if it's not HO. I hear the non HO engines are EFI.

Not to be intruding on this guys post it would be better to answer him first.

 

[75SV1]

MPI is Multi Port Injection. Since the Renix has multi injectors as does the HO, they are both MPI. EFI is electronic fuel injection. Since both are electronically controlled, then they are electronic fuel injection. I think some say there is a difference in that one is sequentially timed and the other isn't. I forget the proper term.
As far as needing a valve job, look at the seats. Are they sharp? Put on some Persian Blue and spin the valves. Doses the blue get wipped off the seat? Or are there gaps? With all that work, I'd probably get a valve job done. Call around and see what the cost is.
Tom

 

[HodgePodge]

You have MPI and TBI both are types of EFI
MPI is Multi-port injection, separate injector for each cylinder
TBI is Throttle-Body Injection, injector/s located in throttlebody

There are Batch, Bank, and Sequential Firing Injectors
Batch is where all of the injectors fire at once
Bank is where half the injectors fire, then next cycle the other half
Sequential is where each injector fires on a separate cycle

Also Renix is a Sequential firing EFI system.

As for the topic at hand, you could have them vacuum test the head for leaks. That will tell you if the valves are seated properly.

 

[Cjmartz2k]

My valve job was only $90--cheap insurance if you already have the head pulled.

 

[John(XJ)Jeep]

Yeah, I got it off now and I looked at it. It seems to be in pretty good shape and all the valves are clean. Theres no corrosion or anything on it so I guess I'm lucky then. I think I'm gonna be changing the seals anyway.

 

[JJacobs]

The seals on a head don't do the same job as the valves do, if you didn't know. Valve guide seals prevent oil from running down the valve stem both in a high vacuum situation (deceleration) and also keep gravity from draining oil down the stem. The valve to seat interface on the other hand seals combustion pressure.

A good way to check the valve sealing is to stand the head up so you can fill a port, and do so with some sort of solvent such as acetone. It is thinner than water. If you don't loose any fluid, the valves will work as is. I'd probably check with a solvent and follow up with a lap job using parts store valve grinding compound and a suction cup.

4.0 heads should be checked for flatness if they've been loose from the block for a while.

Here's an old school mechanic's trick for tearing down heads: lay the head on the floor with rags in the combustion chambers to keep the valves from bouncing on the floor. Use a socket and hammer, a quick rap on each valve will dislodge the keepers and the spring will pop right off.