Cylinder honing - too high mileage?

[stoatmax]

Hi all,

I'm planning on taking my block to a machine shop tomorrow to get the cylinders honed and have wear on the crank, etc. checked, just to be thorough while I have the engine out of the car.

I was speaking with a local machinist/engine rebuilder, and when I told him the mileage on my motor (200k), he told me there was no way I would get away with a simple hone, and that I would need to have the cylinders bored. I wouldn't have any issues with this, if I could find oversized pistons that were affordable. So far, all I've found are forged pistons on SHOnut for $830(!!!)

Is he right? My cylinders aren't in horrible shape but I can feel some light grooves/etc in them, and the previous honing marks are not visible. If this is the case, I have a buddy's engine that has similar mileage but cylinder walls that still show some honing that I could nab the block from. Would this be a better choice?
I'm mostly just looking for advice into my best option to proceed for getting this engine put back together in running shape. I'd rather not spend $830 on pistons if I can help it.

Thanks.

 

[luigisho]

If you have a choice get the best shortblock and go from there. That's optimal. I would consider having it examined before poo pooing anything as the cylinder walls on these motors tend to hold up pretty well however over 200k anything is possible

 

[rubydist]

The fact that the original honing marks are no longer visible suggests your block has more wear than is typical for the SHO engines, since most at 200k will still have original honing lines visible, at least part of the way around the cylinder (in my experience).

What is more important though, in my experience, is if there are vertical scratches in the cylinders. These scratches can come from ring ends or from carbon buildup on the piston sides. If these scratches are deep enough that they will not hone out, then you really need to bore the cylinder. I have successfully rebuilt blocks with some very slight vertical scratches remaining after honing, but its not a good idea.

 

[tompumped]

This is great advice on the vertical scratches. I took apart a subaru motor recently that tested 120(+-5) psi on all four but on a leakdown test the two cylinders with vertical scratches were at ten and twelve percent respectively. In my case it was the piston skirts that caused it after the factory coating wore off, but it's speculation as to the cause of that side only being affected at 170k.

 

[stoatmax]

In that case, Ill almost certainly use my buddy's block then. I'm in CA so i'm pretty sure that's not CARB compliant but i doubt anyone is going to check. I reinspected both blocks yesterday, and his was beautiful with pretty crisp honing marks and no ridges. Mine on the other hand is TRASHED. Between all the cylinders, some have vertical scratches/ridges, some of the ridges are horizontal, and some even have pitting! I've attached some pictures of my cylinders, the first of which shows the worst of the pitting.



I've also uploaded a pic of one of my pistons that shows some damage - I think something got into the intake at some point and really chowdered up the top of that piston and the head.



I find it strange that between the two engines, mine had horrible cylinders but cams that were in good shape, while his had nice cylinders but cams whose lobes were starting to round over. They're likely around the same mileage too (~200k), which makes it even stranger still.

My buddy's block is in such nice shape that I don't think i'll bother even getting the cylinders honed at a machine shop. At most i'll take a few passes at it with a dingleball and call it a day.

However I have a question re: head and cam dimensions.. Since my engine overheated, I plan on using the heads from my buddy's engine. However my cams are in much nicer shape (besides some small putting here and there). I figure the cam bearings are somewhat matched to individual cams, so what i'm wondering is if i can swap my cams into his heads without worrying, or should i inspect the clearance between the cam and the bearings first?

 

[rubydist]

The cam lobes wear on these engines if the shims have issues where the hard surface on the shim comes off and then its rough (the shim). I would put your good cams in the good heads, and then check valve clearances, and adjust as needed. Since you have 2 sets of heads, it is likely you will have enough of the right shims to get everything in spec, but if you don't, just let us know what size shim you need - several of us have a collection of shims from engines we have parted out. You will not have a bearing clearance issue, but will likely have to change some valve shims.

I like your idea of just a little hand honing of the 2nd block, if you can still see all the original hone marks. I've done that on several SHO motors with good results.

 

[luigisho]

That looks pretty beat up. Luckily all the motors I tore into had great cylinders with the original hatch marks and didn't need any work. Toss that thing or you could save it to over bore. I would get rid of it.

 

[stoatmax]

The cam lobes wear on these engines if the shims have issues where the hard surface on the shim comes off and then its rough (the shim). I would put your good cams in the good heads, and then check valve clearances, and adjust as needed. Since you have 2 sets of heads, it is likely you will have enough of the right shims to get everything in spec, but if you don't, just let us know what size shim you need - several of us have a collection of shims from engines we have parted out. You will not have a bearing clearance issue, but will likely have to change some valve shims.

I like your idea of just a little hand honing of the 2nd block, if you can still see all the original hone marks. I've done that on several SHO motors with good results.

I see. I'll swap in the good cams then and swap out the shims as needed. Can the valve gap job be done with the heads off the engine? Also, while I have the engine out of the car, I'd like to exercise due diligence and replace/hone/inspect what I can. So far, I'm replacing rod bearings and piston rings, and any seals I can while I have the engine apart. As well, I'm replacing the heads, head gasket, bolts, and putting in my cams.

Anything else I should replace or inspect? I hear most of the internals in the 3.0 are pretty beefy, so I don't know if I want to bother inspecting the crankshaft or main bearings at all (also considering replacements are not easy to find). Should I clean up / mess with the valves and valve seats at all?

Also, any recommendations on how to clean the mating surfaces between the block and the heads? There's a lot of old copper from the HG I need to get rid of, but I don't want to screw either surface up by removing too much material.

That looks pretty beat up. Luckily all the motors I tore into had great cylinders with the original hatch marks and didn't need any work. Toss that thing or you could save it to over bore. I would get rid of it.

Yeah, I'm surprised by how destroyed it looks considering how absolutely pristine the interior of the car is. I'll probably save it in case I want to bore it for forged pistons, but it's likely just going to gather dust in my garage.

 

[rubydist]

Also replace cam sensor and crank sensor - be very careful when gapping the crank sensor to do it correctly.

The main bearings are not available anyway, and they are rarely worn enough to need replacement, so if the crank rod journals are good, I would not even remove the main caps.

Depending upon what the valves and seats look like, you will either need to lap them or have them ground. Typically the exhaust valves on any engine capture a little carbon here and there and they end up not having real good seat surfaces. You don't want to go to all this work and then have a valve burn right after you put it together, so at least lap them.

You can set the valve lash with the heads off, but you need to check again once they are on and torqued down. On this motor, I've never seen the lash change significantly, but it needs checked anyway.

I start cleaning head gasket surfaces with a hand sanding block with fairly fine sandpaper on it - like 200 or so. You need to be careful on the aluminum not to scratch the gasket surface. On the block, you can scrub away to your heart's content.

 

[Off Road SHO]

There are no cam bearings in SHO's. The cams run in the towers, like most modern engines nowadays.

Tom

 

[stoatmax]

Some updates... I put my cams in my buddy's heads last night. In doing so I've come upon even more questions to ask.

I'd like to make sure I keep my cams/heads in decent shape as new cams don't sound cheap, nor does getting them welded and reground. That being said, I noticed some dissimilarities between my heads and my buddy's.

First off is the number 1 "bearing" cap on what I believe is the exhaust cam of the front (also called "left") head. The surface finish on the inside of my buddy's cap is shiny and has an interesting wear pattern on it (see below)



whereas mine is matte and looks to be in much nicer shape:




Most of the caps are similar in finish to their respective head, as shown above. Right now I have the caps that came from my buddy's head mated to that head, with my camshafts installed. Any reason i should use my caps instead?

As far as using my cams, I mentioned that they were pitted, so i figured i'd throw in some pics and see if anybody thinks they're too pitted to use:




For reference, here were my buddy's cams. Note the rounded over edges, found on all but one camshaft:




Other oddities/questions..

Why does one of my cam chain tensioners bottom out much lower than another, with much less resistance? Is it bad?





As well, it appears the top of one of my buddy's cylinders got chowdered up by debris as well. Will this affect function of the head in any way?




Thanks for all the informative answers so far. I'm glad the SHO community is still alive and well. In other news, after being probably $2400 into this car so far, I just saw another '91 in better shape, with lower miles posted to craigslist nearby, for $1800. Such is life i guess

 

[rubydist]

You should keep the cam caps with the heads that they came from - your caps with your heads, his caps with his heads.

I would not use the cam with those pits in the lobe, it is not a long term solution. From what I can see, the other cams are in much better condition.

The head needs to be cleaned up to see what kind of condition it really is in. The nicks will be okay if they do not have sharp edges / corners to them - the sharp corners can lead to detonation.

The chain tensioner that you can compress all the way down is no good and needs replaced.

 

[luigisho]

You engine and cams are both too pitted

 

[zak]

Just glanced at car-part.com, in CA you can get a 90 K mile 3.2L for like 400, just clean up the piston ring lands, clean the complete EGR system, move your intake cams over. You'll save quite a bit over buying pistons and machining.

 

[stoatmax]

You should keep the cam caps with the heads that they came from - your caps with your heads, his caps with his heads.

I would not use the cam with those pits in the lobe, it is not a long term sol ution. From what I can see, the other cams are in much better condition.

The head needs to be cleaned up to see what kind of condition it really is in. The nicks will be okay if they do not have sharp edges / corners to them - the sharp corners can lead to detonation.

The chain tensioner that you can compress all the way down is no good and needs replaced.

You engine and cams are both too pitted

Ah, I didn't know the pits were such an issue. I guess I'll use the slightly chamfered cams then.

Just glanced at car-part.com, in CA you can get a 90 K mile 3.2L for like 400, just clean up the piston ring lands, clean the complete EGR system, move your intake cams over. You'll save quite a bit over buying pistons and machining.

Holy crap, where has the site been all my life??? I would've never guessed there'd be such a good resource for buying used car parts. Well now that I know that exists I'm definitely going the cheapest route I can considering that, if at worst my engine dies, I can grab a new one for a few hundred bucks.

Is the 3.2 a direct swap into first gen SHOs?

 

[rubydist]

The front (left) head is different, so the alternator will not mount unless you cut off the mounting boss that is in the way. The front accessories will need to be changed to the 3.0 style 2-belt system, or you will need to fabricate a custom motor mount. There is a thread here that details the custom mount. (If you do the custom mount, and use the 3.2 front accessories, then you do not need to modify the left head.)

 

[luigisho]

I think there was a line of reasoning that pitted cams might spit out a shim during operation. That discussion (and maybe real occurrence at that time) was way back. Not sure if that is still archived on the forum or not.

 

[Devin]

Is that from some sort of suction action with oil stuck in the pits?

 

[luigisho]

Honestly I don't remember the details vividly I only recall the discussion was had back then. My rule of thumb is, if it looks funky get rid of it. At least with the v6 cars, there are still enough used parts around to make me not have to make a damaged part work. I just have so little free time to do work myself (although I will try and squeeze it in when I can) I can't roll the dice and redo work with known iffy parts... Except for crappy reman alts and starters-- I already budget that in

 

[stoatmax]

I think there was a line of reasoning that pitted cams might spit out a shim during operation. That discussion (and maybe real occurrence at that time) was way back. Not sure if that is still archived on the forum or not.

Yikes! That doesn't sound like something I'd want happening.


Funny enough I may be able to put off this rebuild a bit. I'm in talks with the guy selling the $1800 '91, as I may just buy that car, use all the 60k components I bought for it instead, and set aside this SHO as a parts car/future race car. I didn't *really* want a 4th car, but this will allow me to at least get rid of my datsun and BMW if all goes well. Also it'd be nice to have free time again, I forget what it feels like.

Also that 91 only has 107k original miles so if my goal is as little car work as possible for as long as I can, then that's almost certainly going to be my best bet.