Need advice on machine shop error on Ford Mod block

[Crazy Dirt]

I’ve got a Ford 5.4L modular block in my shop that I’m rebuilding and since the required bore tolerances are tighter than what I can produce here, I sent the block out for a 0.010” over bore and hone. I also included the box of pistons, (which Mahle has written on the boxes info tag to provide 0.0014” clearance) and sent the block in with torque plates and main caps already torqued. The machine shop knew this ahead of time and we were on the same page. The book calls for a piston to wall clearance of 0.0010” - 0.0018”, and a maximum taper of 0.0002”.

What I got back was machine work that ranged from 0.0021” - 0.0030” piston to wall clearance and taper as much as 0.0005”. If you were told that this was close enough for a modular block, would you believe them? This shop is new to me and is the first time I’ve used their services. I’ve heard good things about them, and while I want to give them the benefit of the doubt that this is close enough, this isn’t my first rodeo either and my gut is that these are way too far out of spec to just bolt up and run.

For those that are interested in seeing all the bore measurements, I will attach a picture of the measurements I’ve taken. They are written in tenths with the 0 point being the piston skirt, so 24 is 0.0024” of clearance.

Thanks in advance for your help. I am much more experienced with diesels and this is the first time for me doing significant work on a modular engine, so I’m open to the idea of being wrong.

[fordified]

Forged or hypereutectic pistons? Either way, I wouldn't think twice about running it with 3 thousandth clearance.

[Crazy Dirt]

They’re hypereutectic with coated skirts and moly faced rings.

[mag2555]

I would run it as is!
Have you also mic’ed up the pistons in four to 6 locations each to see how accurately they are machined?

Do they show a .0002” veriation or more on any of them by chance?

[BillK]

Where are you measuring the pistons ? Mahle usually has a sheet with their pistons saying at what point to measure them. I have to assume that you are measuring the bores with the torque plate still on ?

How are you measuring the bores ? Bore gauge ? If so are you setting it with the same micrometer that you are using to measure the pistons ?

The one thing that bothers me is that a lot of coated pistons simply cannot be measured and you have to go by the bore size on the box label. If you are measuring on the coated part of the piston they are probably even looser than what you think.

Its a tough call. I would call Mahle Friday and ask them and see what they say. Most piston manufacturers do state that the clearance figure is a "minimum" and do recommend more clearance for high performance use, especially with any type of power adder. What is the application ?

If the bores are .010 oversize they should be measuring about 3.561 - 3.562 ?

What part number piston ?

Just thinking out loud

[fordified]

They’re hypereutectic with coated skirts and moly faced rings.

The clearance for hypereutectics can be pretty tight, but the thing's not going to blow up with .001 more clearance. That's .0005 per side extra clearance. I can't see getting piston slap or noise from that.

As others have said make sure you're measuring the pistons at the right spot. I would measure each one and put the largest one in the .003 hole. Also, if you're going to lean on the engine, a little extra clearance is not a bad thing.

[BCjohnny]

All things being equal I doubt it's the best hone job specs people have seen, but will it cause you a problem ...... I wouldn't have thought so

However, is it what you discussed prior and paid for ? I think that's your problem ...... I'm guessing you've gone in with particular requirements and they've not been met ?

It's not that hard to hold less than five tenths ...... less when needed ...... on decent equipment, so I think I'd have made a big deal of telling whoever machined it that you were going to get in there with a tenths gauge when you got it back

Most customers have never seen a tenths gauge, let alone own & use one ...... so it's I think it's fair to say you're a 'sloppy' machinists potential nightmare

[Crazy Dirt]

Thanks guys for the input, I appreciate the brainstorming as it helps me run through things in my mind and make sure I didn’t miss something.
To answer the questions:

- The application is basically stock OEM in an on-road / off-road / remote access pickup. Reliability and drivability are most important. The truck will, as far as I know, always be NA and stay around 350hp at the crank. The goal is to do a rebuild of better quality than the local options for a reman long block (only one option up here in this corner of Canada and they’re the same outfit that supplied the not-so-good remans for the dealership when I worked there. It would be safe to say that quality control wasn’t that rebuilder’s selling point.

- I’m measuring the pistons only 90 degrees to the pin as it’s the widest spot on these pistons. I did mic one piston in multiple locations just to confirm that this is the widest point. Mahle specs the point to be 0.850” up the skirt. However there is no window on the skirt coating so I am including the thickness of the coating in the measurements, which as Bill points out doesn’t work in favor of already oversized tolerances. There is a 0.0002” variation among the 8 pistons. Given that this is being measured with the coating, I’m happy with that.

- Correct on the 3.561 bore size. I’ll attach a picture of the box tag for any others that are as weird as me and enjoy looking this stuff up lol.

- I’m measuring with a Mitutoyo tenths bore gauge, and am using the same micrometer to measure the pistons as I am to set the bore gauge. The torque plates were off when I picked up the block but I am measuring with them back on and with the mains torqued, including side bolts.

I think BCJohnny is right about the sloppy machining. What annoys me is that I was straight up with him, asked him beforehand if he could work to the specs and was told no problem with the diamond hone he’s running. I told him upfront that I would be checking it (including with a profilometer) before assembly (and he did a good job on the surface finish) maybe he didn’t think I actually had the means to check the work. I even make it a habit to send in an overview sheet when I send something out for machine work, in this case it listed required surface finish and bore sizing, torque specs and procedures in case he needed.

I guess at the end of the day I’m less concerned about the cost and more concerned about whether I’m going to regret putting this thing together and out the door when part of the job is out of spec. I think that’s a good idea to call Mahle and see what their take is on it. Thanks again for the feedback. This modular block is a good learning experience if nothing else.

[mag2555]

You have stated that your measurements where with the plate back on and other things torqued up, but did you have the heads gasket the will actually be run sandwiched in there also?

[BillK]

CD,
If it makes you feel any better I will say that I don't personally think you will have any problem at all. I would be willing to bet that your block is finished better than 75% of the factory ones as far as bore size, taper and roundness. Unless the customer specifies otherwise I typically finish blocks .0005" big. I would prefer it to be a little loose rather than too tight any day. Cant say I have ever seen an engine hurt in any way by an extra thousandth of clearance but I have seen what happens when they are too tight

Let us know what Mahle says, I am curious.

[MotionMachine]

What Bill said about factory tolerances. I have a perfect example for this topic. Local Ford dealer sent me a new 351W block to measure, as the assembling mechanic thought the bores felt loose. This new block was replacing a cracked block and was getting the original internals. The block came with a line card detailing the machining tolerances. Bore size was listed as 4.0000"- 4.0040". The bores were right at 4.004". It was "in spec" so it went in the truck with .006" PTW. Ever since that day I don't worry so much about going over half a thou.

On another note, I've learned that locking the spindle on a mic when setting a bore gage can change the mic's reading by as much as .0005". If using a non Sunnen gage, I keep the spindle unlocked and just check to make sure it didn't move when setting the gage. I figure that when you check a mic on a standard, there is some slight push against the spindle, same as the slight spring pressure in the gage. I'm open to opinions or experience on this theory.

[Paul Kane]

I agree it’s okay in this case, especially given the application.

Regarding the primary issue of the finished work not meeting the specified standard as requested: long, long ago when I was outsourcing machine work for my own builds, I would go to pick up my machined parts with my measuring instruments in hand. Initially I was getting smirks from the machine shop owner, but I’d also reject parts on the spot when they weren’t finished to my call-out. It did not take long for aaaall for my outsourced parts to start measuring to exactly what I specified.

[Crazy Dirt]

Just got off the phone with Mahle and learned some interesting stuff. Calling them was a good recommendation, thank you.

The coatings on the skirts are another 0.0005” per skirt, so there is automatically 0.001” extra clearance by design. He said that my concern was on point as these (iron Ford mod blocks) are one of the worst engines to go over spec on, especially with Hyper-eutectic pistons. At 0.003” over bore tech support said there will be noise and a lot of it and that they should not be run. Ideally these should be run at 0.001” - 0.0014” clearance, and that they will be happiest at 0.001” and will run a full lifespan at this clearance.

Not the news I was hoping for but at least it’s fairly definitive.

[BillK]

Just got off the phone with Mahle and learned some interesting stuff. Calling them was a good recommendation, thank you.

The coatings on the skirts are another 0.0005” per skirt, so there is automatically 0.001” extra clearance by design. He said that my concern was on point as these (iron Ford mod blocks) are one of the worst engines to go over spec on, especially with Hyper-eutectic pistons. At 0.003” over bore tech support said there will be noise and a lot of it and that they should not be run. Ideally these should be run at 0.001” - 0.0014” clearance, and that they will be happiest at 0.001” and will run a full lifespan at this clearance.

Not the news I was hoping for but at least it’s fairly definitive.

Ouch,
So now what, go to the next oversize ? And have a talk with the machine shop ?

[fordified]

I did a quick search and see that the Mahle power pack deal is about $800. Instead of buying a new set, you could have the pistons recoated with a thicker layer to bring them into spec. A lot of guys do that with race engines that are honed between seasons where the clearance increases too much. Usually, the pistons are forgings that cost over $1000 a set with rings in the same neighborhood.

It's not ideal for your application but did want to mention it. I've never used them, but line-to-line has been mentioned as a good source for coatings. I've always used Calico. You'll probably find it hard to get the machine shop to pay for their mistake but that's also an option to pursue.

You'll get it squared away. It's nice to see someone who's diligent about engine building.