What's new
By:
Filters

3.7/4.7L heads... How bad is too bad?

u2slow

u2slow

Hermit
Joined
Mar 20, 2021
Member Number
3695
Messages
651
Loc
BC
So the jeep has suffered a dropped valve seat. I dig into the spare engine (blown HG) to steal that cyl head. Its distorted between the cyls to let a .0025" feeler gauge pass under it.

IMG_20240127_182111439_HDR-01.jpeg

Is this realistically going to seal with a new HG? Any HG's better than others? (Most are mls 3 layer steel). One buddy said to spray the gasket with copper hi-tack and send it.

I'd like a fresh head, but i cant afford the downtime at this juncture. I'd rather have this run a few more months while i assemble a more long-term engine.

Opinions? :homer:
 
I'd try a straightedge that's designed to be used as a straight edge rather than a measuring stick. I wouldn't trust that home depot thing to be straight.
 
I don't have a manual that covers that engine handy but even if the "straight" edge is straight 2.5 thou is probably just under/over the spec. I wouldn't run it without resurfacing.

Not rocket science to resurface an aluminum cylinder head at home. It'll cost you a couple hours, a little more if you don't have a good flat reference surface and you've gotta use finer grit and measure more frequently. Don't even need to pull valves and shit, just block passages to keep any dust out.
 
It's been a while, but that last time I had a head resurfaced at a machine shop they had it done in a few hours for under $100. It's a relatively quick operation. Call around and get it done right.
 
I have the better (Felpro) gasket showing up tmw at 4x retail price. Dont have a surface flat enough to hand-finish the cylinder-head deck.

No specialized service is quick or cheap here. Not even a reply from the one local machine shop yet.

I was hoping for a success story at the 2.5 thou' warpage.... but i guess not.

I have about 3 days to get this running again. I can afford to throw out $100 and all the labour on this gamble. A proper fix is looking like at least a month out.
 
Best we can do here is old house windows and 8.5x11" sandpaper. 5 thou to clean.... would have been at it a while :homer:
 
Slight thread derail but


I read service manual for 12v Cummins on cylinder head R&R.

It say to use orbital sander. I might will try that if I’m that desperate and cheapass frugal.

IMG_2639.png
 
IowaOffRoad said:
In the future, if you can find a good sturdy piece of glass and a long enough sheet of sandpaper you can get it to a thou or under with that.
Click to expand...
You need a reference surface to check it as you go. There's technique that goes into it and it's real easy to get a bananna shaped head if you don't either a) have a reference surface to frequently check against b) know what you're doing.

"Lapping techniques" are what you want to Google. This is 500yr old shit they had to learn the hard way to make the first precision optics in the 1500s or thereabouts.

The reality is that you can get away with a lot of shit just fine if you don't mind the replacement gasket lasting half as long as the original.
TrailTamer said:
I read service manual for 12v Cummins on cylinder head R&R.

It say to use orbital sander. I might will try that if I’m that desperate and cheapass frugal.
Click to expand...
They know the average tech is in too much of a hurry to dig a hole in anything with 400-grit even if he has an orbital. :laughing:
 
Last edited:
arse_sidewards said:
You need a reference surface to check it as you go. There's technique that goes into it and it's real easy to get a bananna shaped head if you don't either a) have a reference surface to frequently check against b) know what you're doing.
Click to expand...
if you have a fairly new piece of thick tempered glass and a piece of sanding cloth big enough (think 12” wide belt sander cut apart at the seam) to cover the entire head it will do just fine. Keep it wet and moving. I’ve got a precision straight edge and access to a granite block. If you do as I suggest I’ve never found it anything but flat with either method of measurement. You can even wipe a piece of old t-shirt down with buffing compound and stretch it tight over the glass if you want it to have a smoother surface. Aluminum is tougher with sandpaper because for this method you’re inclined to use coarser paper because finer paper clogs faster. 220/240 wet is coarse enough if you wash it down frequently (do it outside and spritz it with the garden hose every couple minutes). Cast iron, you can get away with 120/180 final. If it’s really bad I’d start with 60/80. Use a swirl motion and HG will seal better. A bit of practice and it will look like the machine shop did it.
If you’re going to use a 150yo piece of single plane farmhouse glass that was wavy when new and a 1/3 sheet of paper then you get what you deserve.
 
IowaOffRoad said:
if you have a fairly new piece of thick tempered glass and a piece of sanding cloth big enough (think 12” wide belt sander cut apart at the seam) to cover the entire head it will do just fine.
Click to expand...
Glass that big will flex and deflect enough to matter. I've tried it.

Checking your work as you go is foolproof and good technique will go a long way.

My best setup so far is a small thin surface plate with a handle on it.
 
arse_sidewards said:
Glass that big will flex and deflect enough to matter. I've tried it.

Checking your work as you go is foolproof and good technique will go a long way.

My best setup so far is a small thin surface plate with a handle on it.
Click to expand...
Then you tried it wrong. What were you doing, throwing it between 2 sawhorses? Support it on a solid bench.
ETA: take it out of the frame.
 
I had it on rubber on my steel workbench.

You're being an idiot. A big floppy piece of glass and crossing your fingers is just not equivalent to good technique and actually checking your work as you go.

I'd rather glue sandpaper to plywood and check my work than use "probably good" glass or counter granite. Sure you might get good enough results if you're dragging a small head across a big piece but anything with 4+ cylinders is getting big enough to be inconvenient and the abrasives are gonna get expensive.
 
You ever stop and think that maybe you aren’t as good as you think you are? Don’t use floppy glass. 1/4 inch tempered reinforced glass is what I’ve got. It’s not “floppy”. It’s dead straight with nothing on it and with a V8 cast head on it.
I also said “with a little practice”, of course you should check it periodically, but if you don’t know how to check it properly or lack something straight enough you’ll fuck yourself harder trying to “fix” what ain’t broke.
Just because you try something once or twice and it doesn’t work for you doesn’t mean it doesn’t work.
Hetero sex works for most of the world. Don’t declare it’s bad just because you couldn’t get the hang of it. :flipoff2:
 
Small surface plate and moving the plate instead of the work is the best method I have found so far in terms of both speed and results (and flexibility, can do decks in the car).

While other setups certainly can work it's dumb to tell someone to go for them and learn the improvements the hard way when they can just skip right to the end. If you're good about checking and correcting as you go you can get away with straight garbage.

Heck, I'd be tempted to try the orbital with some really fine paper. Can always un-fuck it if it doesn't work out.

IowaOffRoad said:
You ever stop and think that maybe you aren’t as good as you think you are? Don’t use floppy glass. 1/4 inch tempered reinforced glass is what I’ve got. It’s not “floppy”. It’s dead straight with nothing on it and with a V8 cast head on it.
Click to expand...
All glass is pretty floppy in typical glass thicknesses. Heck, my inch surface plate will deflect if I use it wrong. I'd rather use a granite countertop than glass on an unknown workbench.
 
You must log in or register to reply here.
Top Back Refresh