head job

[hihosilver]

I need to do a valve job on my 86 300e( guides)and I picked up a head from a 89( iwas told) so I could do the valve job and have the head ready to go, I already bought new guides and valves does any one know of any problems should look for besides checking the head for cracks, the head cam with the cam and rockers also, thanks

[Tx Benz]

Originally Posted by hihosilver

I need to do a valve job on my 86 300e( guides)and I picked up a head from a 89( iwas told) so I could do the valve job and have the head ready to go, I already bought new guides and valves does any one know of any problems should look for besides checking the head for cracks, the head cam with the cam and rockers also, thanks

Make sure the head you have does not have the air fitting about 1/2 way back the exhaust side.
MY 90 and up cars had air injection, 86-89 did not.
Tell your machine shop to not use "whiz wheel" grinding discs on the head.
These cause more problems than they solve,IMHO, and are not allowed in our building. Be sure rockers are numbered when removed, and reinstalled in the same position.

[theairboy]

In case the head isn't good you should have them check the amount of head thickness to be sure it wasn't cut before and possibly leaving not enough metal to get a good surfice on it. before you spend any money on the other procedures to get it ready.

G-luck

[rstallings]

I would suggest chasing all of the bolt holes on the cam caps, then assembling the parts w/o the cam and torqueing to spec. Stripped holes need to be fixed, and it is a real common problem on most aluminum heads. Put antisieze on the bolt threads when you do this.

Check the exhaust studs and tapped holes as well. These also strip. Take the nuts off the studs and make sure you have a set of undamaged studs and nuts. Buy new fasteners if needed, these parts are cheap (don't buy replacements from Home Depot) , and you will be glad you did.

Intake bolts/studs should be ok.

I personally like to helicoil all of these holes as a matter of routine.

Make sure the head is not warped. If it is, you need to look at the cam bearings. All of this can be fixed if it presents itself.

If the donor engine was run out of oil, chances the cam bearings will be scored. If you get them fixed, you may have to replace the cam. If you go with a used cam, get the rockers and followers with it. Some cams are hardened, others are not. The correct rocker must be used with either cam. Keep everything in its original order.

I like to take the rocker shafts out of the cam caps to clean the parts well. Nasties can hide in some places that are impossible to clean as an assembly. Use a heat gun to warm the aluminum parts, and the steel shafts will slide right out. Keep everything in order. Clean. Reassemble, using the heat gun trick again. I like moly assembly grease.

The heat gun will also make removal of the distributor rotor mount on the end of the cam easier. Don't worry about frying the seal, you will replace it.

Don't take the valves out unless you have a good spring compressor and know how to use it.

Measure your head bolts for stretch. I doubt it will be an issue.

While you're in there, I would replace the timing chain, the tensioner, and both guide rails.

Everybody has an opinion about sealants. I hate silicon. I like anaerobic sealant, and Hylomar.

If you decide to scrape the carbon off the top of the pistons, tape the coolant passages off and use a cheap plastic or wood scraper. One bristle from a wire brush can ruin your engine, so avoid them.

I use paint stripper and a razor blade to clean gasket residue off the block. I like to stuff rags into the cylinders with the down pistons.

If your water pump is shot, now's your chance. Replace the hoses on the Idle air valve, because they will probably be done.

Make sure all of the holes in the oil pipe on the top of the cam are clear.

This engine uses stretch bolts. I don't want to insult you, but make sure you are sure of the concept of 90 degrees, and can measure this either visually, or buy an angle torque gauge.

Get the exhaust studs in order before you put this back together. install the studs by using a jam nut, then put the new gaskets, manifolds, then the nuts.

[hihosilver]

thanks for the good tips, is there a difference in the guides between the years as i have read posts on the 86 & 87 but can't remember when they changed, the first thing after work today I will check the head for a warp. I just finished fixing a nisson head for a friend I had to mill .009 off to straighten then shim the cam towers to fix the cam