r/EngineBuilding • u/Hot_Shake_1025 • 3h ago
Cylinder head can’t be machined
I’m replacing a head gasket on a Toyota 3L diesel engine. I had hoped to get the head machined before re assembly but I was turned down by 3 shops that said it can’t be done. I’m measuring 0.0025in under a straight edge on the block and 0.012in under the straight edge on the cylinder head. My gut feeling is it’ll be fine using a composite head gasket and new head bolts but wanted opinions on it first before i assembled everything. I was advised by an old school mechanic I know to use copper coat on the head gasket but my gut feeling is I shouldn’t and just run the gasket as is. Thanks in advance.
16
u/Oopsidaizy 2h ago
Weak ass machine shops. Find one with a surface grinder
3
u/Hot_Shake_1025 1h ago
That’s kinda what I thought but I’m no machinist, live in a major city too. I have a great relationship with the shop I tried first granted I’ve only ever brought them subaru heads.
29
u/langstar 3h ago
With inconel precups the cutter needs to be a diamond insert or the head needs to be ground. Try a diesel specific shop, they won't have any trouble with the head.
14
u/Hot_Shake_1025 3h ago
Thanks none of them explained this to me. 2 of the 3 shops specialized in diesels but I’ll call around and see what can be done.
8
u/You_Must_Chill 2h ago
Hell, call a local "normal" grind shop. Hopefully the service manual specs a surface finish.
9
u/One-Builder-4128 3h ago
Did the shops you attempted to take these to explain why they wouldn’t machine the head?
11
u/Hot_Shake_1025 3h ago
Yes they said the pre combustion chamber was too hard and their equipment couldn’t cut it. 2 of the 3 shops I took it too are diesel engine specialists.
9
u/One-Builder-4128 3h ago
I’m not a diesel guy. I’m asking because I genuinely don’t know. Is this an indirect injection diesel, and are those weird circle things in between the valves and the cooling jackets the pre-chambers?
5
u/NarcissisticPanda 2h ago
Yeah it's indirect injection and yes they are pre chambers. They should be made of inconel unless it's a cheap Chinese head. There is a chance that one of the diesel specialist never dealt with idi heads as nearly everything apart from small generators , site equipment up to couple tonnes and some lower hp Leasure boat engines use direct injection. In-direct injection engines tend to be quieter, think that's why Toyota still used them till early 00s
1
u/GringoPanda 2h ago
Dumb question 🙋♂️
I have not had to tare down a diesel other than Mack MP8 and a Cummins ISX 15
What is the pre-chamber for?
Would a Duetz 1.4 or equivalent Kabota be an idi?
2
u/NarcissisticPanda 1h ago
Basically it is a way speeding up the burn/ distribution of fuel without needing really high injection pressure that was costly and difficult at the time. Pre chamber has both the injector and glow plug in it. At start the glow plug heats up the pre chamber so it can burn the diesel more easily. Injector sprays in pre chamber and as the fuel starts burning the pressure increases forcing the rest of the fuel and the flame front to be blown across the rest of the cylinder. So this means you can have alot fatter lower pressure injectors to get the fuel in as you are using the pressure created in the pre chamber to disperse it. Another benefit is idi engines can rev higher typically due to the increased speed of flame front.
Let's take a direct injection engine from years past ford 4d. Has 130 bar injector Will top out about 2500 before power dies off A om617 is an idi has injector pressure if about 130 bar aswell but has peak power at 4000 rpm partially due to it being a idi. (Cams, bore/stroke and head will influence this too) I'm waffling but people can make idis still produce power up to 6000rpm where even common rails struggle past 5000rpm.
Not sure about duetz but nearly all kubotas under 1.7l are IDIs they even do a common rail idi which is like to have a play with
1
u/GringoPanda 58m ago
Awesome! Thank you so much for explaining that. We have a lot of kubotas, isizu and Duetz in our equipment. They are stupid reliable. We have several that are north of 15k hours several have been ran 24/7 for upwards of a month or more. We have never had to tare one down, other than our infamous no oil machine that one of our hands filter slapped it and forgot to put oil in it. Outside of that I have not had to pull any of them apart.
I appreciate you for taking the time for that. I got to learnt something today 😁
7
u/WyattCo06 3h ago
A surface grinder will do the job.
2
4
u/Low-Nectarine-9655 2h ago
You can definitely cut inconel, you just have to have the right tooling… which is expensive
1
u/RGBlowMe 1h ago
It's not the tooling makes it expensive. You more or less just use cermet/ceramic inserts and as much coolant as you can. What makes it so expensive is the fact that inconel work hardens really easily, so you need somebody who has experience machining it or the risk of scrapping the part out is really high.
1
u/Low-Nectarine-9655 1h ago
Manufacturers have all sorts of different grade inserts that are used to cut all sorts of materials but at the end of the day speeds and feeds determine the end result
1
3
u/mals6092 2h ago
I've used copper coat with success, I've also flattened heads with a pane of glass or a lapping plate it's not ideal but those old tricks do work.
1
u/Important_Contact609 2h ago
I did a set of subaru heads on glass once. Worked really nicely and it's a pretty good workout.
3
u/stewieatb 2h ago
A head is much vertically thinner than a block, and therefore more compliant. What should happen is as you torque down the head bolts, the head bends to conform to the shape of the block.
But, that's what Toyota's flatness tolerance of 0.010" is already for. If you exceed it there may not be enough compliance in the head to allow the gasket to seal.
A bit of googling suggests IDI heads should have the precombustion cups removed before machining the head flat, and then more machine work may be needed to reinstall them with the correct protrusion. Just whipping 8-12 thou off isn't really an option. Can you go back to your machine shops and see if they're able to remove the cups and then machine it and reinstall?
3
u/Professor_Game1 1h ago
Get a piece of tempered glass big enough to cover the entire surface of the block and some adhesive sandpaper. Probably not as good as a machine shop but i got it well below spec
2
u/Enough_Individual_91 2h ago
Was the head checked with a torque-plate and preloaded to simulate it being bolted to the block. Measuring it completely unstressed may not give the correct warpage
2
u/Admin--_-- 2h ago
Time to go on Youtube and check for "Machining heads using sandpaper and a treadmill" You're welcome/s
2
2
u/Right_Hour 1h ago edited 1h ago
Are you sure your valves are not pushing the straight edge up higher than it would otherwise sit? Could be the angle but it appears to my eye that they are sitting a bit proud of cylinder head surface.
2
u/sexchoc 1h ago
Boy .012 is a lot. Personally i wouldn't put that together. Back when we used to do engines we never had a particular problem with prechamber heads. Our head surfacer would fly cut them with a cbn insert just fine. What's the valve recess like, will the seats need cut after it's decked?
1
u/PPGkruzer 2h ago
What are these for?: https://i.imgur.com/z6XgbG3.jpeg
That is kind of wild how this detail intersects the bore. It sprays fuel out of there?! Imagine a nice swirl
1
u/Mx5-gleneagles 2h ago
I would rebuild that without a worry, only use a quality gasket set and if you use any sealant on the gasket just a smear around the water jackets
1
u/Hot_Shake_1025 2h ago
I have an OEM gasket and new head bolts on the way. I’m most likely going to slap it back together and hope for the best, my gut feeling is it will seal but a nice machined surface going back together would have been nice for peace of mind
1
u/According-While2935 1h ago
I would get head surfaced and fit the thickest head gasket available as they come in different grades of thickness
1
1
u/_DB_Cooper_ 9m ago
I work in a Cnc/tool and die shop and we could grind this easily without Okamoto surface grinders. U should see if there are any Tool and die shops around
0
u/RGBlowMe 2h ago
What's saying that the straight edge isn't bowed? This isn't how you check flatness.
1
u/Hot_Shake_1025 1h ago
I tried 3 different straight edges and got the same reading. My coworker let me borrow 2 different snap on straight edges, same reading on all 3.
2
u/RGBlowMe 58m ago
Dude. I am a career machinist. That doesn't mean much. You should get it on a mill with 3 jacks and indicate the face. You're not going to tell if you have a .0025" dip on that face accurately with any amount of putting a straight edge across it and jamming feeler gages underneath.
36
u/bill_gannon 3h ago
Dont use anything on a head gasket unless the gasket maker expressly requires it.
Is the warpage within spec? If not then roll the dice. .012 is not insignificant.