Some Engine Rebuild Questions

[dice2012]

Hi all, I'm currently in the midst of building my m20b25, and I am getting to the point where I will have to send stuff off to the machine shop. This is my first engine build and I want to do this right, so I have a lot of questions. Unfortunately, most of these questions I either can't find the answers to, or they're just not out there.

For context, I started this as I had pretty bad piston slap ever since I bought the car, and it only got slightly worse while I had it. After disassembling, the rod and main bearings looked completely fine with no wear; all of the piston skirts had noticeable wear, with piston 1 being the worst. At least half of the cylinders are right at that out of round maximum spec, with the others just under it, so I plan on replacing the pistons with new +0.5mm pistons, and overboring to accomodate.

If I get the cylinders overbored, do I need to get the deck blocked as well? As far as I can tell, the block surface is completely flat, with no warpage or markings. Also, I assume I will have to get pistons balanced, but is it acceptable to skip balancing the conn rods since they are being reused? On top of that, is it fine to reuse conn rods? The machine shop I went to told me that (without measuring) I would have to replace them with the pistons, but I'm not so sure.

Regarding the intermediate shaft, will a thermal cleaning (i.e. baking the engine and getting the dried gunk off with steel shot) ruin the bushings or needle bearing there? I know that hot tanking will wreck them, but I haven't seen anything about the thermal method. I'm even wondering if I should just clean everything by hand, since I am prepared to remove freeze plugs/oil gallery plugs myself, and wouldn't mind saving on cost where I can.

For the head, what is the maximum allowable warpage? I am able to get a 0.003"/0.08mm feeler under a straight edge in the middle with some resistance. I don't believe I can get a 0.004"/0.1mm feeler under. I don't have a mic big enough to measure the head, but my digi caliper is showing the head height to be around 124.9/125.1mm, so it may have already been skimmed before, or my caliper skills might just be subpar lol.

If this warp is unacceptable, am I limited to decking the head by a few thou? I've read about a method of heating/cooling the head with shims, but not sure if I have the means to do that myself, or if the machine shop would do that. I guess I am just worried about the head warping further and binding up on the cam.

Can I reuse a clutch/flywheel if it wasn't slipping and doesn't seem to have hotspots or crazy looking wear?

Finally, am I overlooking getting valves/valve guides replaced? I measured the intake and exhaust valves, and the stem diameters came out to 0.275" for intake, and 0.274" for exhaust, but that seems to be standard for replacement valves. I used an intake valve to measure the guide wear, and found the intakes were all around 0.4mm of play, and the exhaust guides were around 0.5-0.6mm of play. I know the maximum guide wear is between 0.8mm-1mm, but am I fine to just slap on new valve stem seals and reuse my old valves/guides? I did the water trick in the bentley guide to check valve seat sealing, and everything was good! So I am a bit apprehensive to replace the guides and valves if I don't need to.

I know this is a lot of questions, but I appreciate any wisdom, and let me know if I am overlooking anything or just overthinking! Thanks :)

[82eye]

Hi all, I'm currently in the midst of building my m20b25, and I am getting to the point where I will have to send stuff off to the machine shop. This is my first engine build and I want to do this right, so I have a lot of questions. Unfortunately, most of these questions I either can't find the answers to, or they're just not out there.

For context, I started this as I had pretty bad piston slap ever since I bought the car, and it only got slightly worse while I had it. After disassembling, the rod and main bearings looked completely fine with no wear; all of the piston skirts had noticeable wear, with piston 1 being the worst. At least half of the cylinders are right at that out of round maximum spec, with the others just under it, so I plan on replacing the pistons with new +0.5mm pistons, and overboring to accomodate.

if the cylinders are badly ovalized they may also have tapered themselves. one or both conditions would normally make the block a hard pass for rebuild.

If I get the cylinders overbored, do I need to get the deck blocked as well? As far as I can tell, the block surface is completely flat, with no warpage or markings. Also, I assume I will have to get pistons balanced, but is it acceptable to skip balancing the conn rods since they are being reused? On top of that, is it fine to reuse conn rods? The machine shop I went to told me that (without measuring) I would have to replace them with the pistons, but I'm not so sure.

most of that will depend on the condition of the old parts. if you rebalance, rebalance everything. i re-used pistons and rods in my build, but the shop deemed them worthy and my goals were not that big.

Regarding the intermediate shaft, will a thermal cleaning (i.e. baking the engine and getting the dried gunk off with steel shot) ruin the bushings or needle bearing there? I know that hot tanking will wreck them, but I haven't seen anything about the thermal method. I'm even wondering if I should just clean everything by hand, since I am prepared to remove freeze plugs/oil gallery plugs myself, and wouldn't mind saving on cost where I can.

there are methods that won't destroy the babbitt bearing. most generic shops often don't care so choose your shop carefully.

For the head, what is the maximum allowable warpage? I am able to get a 0.003"/0.08mm feeler under a straight edge in the middle with some resistance. I don't believe I can get a 0.004"/0.1mm feeler under. I don't have a mic big enough to measure the head, but my digi caliper is showing the head height to be around 124.9/125.1mm, so it may have already been skimmed before, or my caliper skills might just be subpar lol.

zero warp is the goal.

If this warp is unacceptable, am I limited to decking the head by a few thou? I've read about a method of heating/cooling the head with shims, but not sure if I have the means to do that myself, or if the machine shop would do that. I guess I am just worried about the head warping further and binding up on the cam.

zero warp is still the goal.

Can I reuse a clutch/flywheel if it wasn't slipping and doesn't seem to have hotspots or crazy looking wear?

flywheels can be resurfaced. you can also go to a new lightweight depending on your goals. replace the rest of the stack.

Finally, am I overlooking getting valves/valve guides replaced? I measured the intake and exhaust valves, and the stem diameters came out to 0.275" for intake, and 0.274" for exhaust, but that seems to be standard for replacement valves. I used an intake valve to measure the guide wear, and found the intakes were all around 0.4mm of play, and the exhaust guides were around 0.5-0.6mm of play. I know the maximum guide wear is between 0.8mm-1mm, but am I fine to just slap on new valve stem seals and reuse my old valves/guides? I did the water trick in the bentley guide to check valve seat sealing, and everything was good! So I am a bit apprehensive to replace the guides and valves if I don't need to.

do a full refresh of the head or don't bother opening the engine at all.

I know this is a lot of questions, but I appreciate any wisdom, and let me know if I am overlooking anything or just overthinking! Thanks :)

there will be a ton of things that come up. the guys here will help you through it. there are some amazing builds here and several different levels of skill.

[dice2012]

if the cylinders are badly ovalized they may also have tapered themselves. one or both conditions would normally make the block a hard pass for rebuild.

I'll try to upload my cylinder measurements. IIRC, max out-of-round is 0.03mm, and max conicity is 0.02mm. From what I measured (I will need to go back and double check), the maximum difference in measurements (front to back vs side to side) is 0.02mm, and the difference between just about every measurement top to bottom is 0.02mm. So is that considered too tapered? But wouldn't an overbore fix this?

there are methods that won't destroy the babbitt bearing. most generic shops often don't care so choose your shop carefully.

What methods are these? I have looked over just about every forum post and couldn't find the answer.

zero warp is the goal.
...
zero warp is still the goal.

Is the best method to skim or try to straighten the head with tension first?

do a full refresh of the head or don't bother opening the engine at all.

I just get uneasy thinking about spending $$$ on valve guides/seats/valves when the clearances are still below the factory max spec. How much should I be looking to spend on that, reasonably.

there will be a ton of things that come up. the guys here will help you through it. there are some amazing builds here and several different levels of skill.

Yeah thank you for the help so far!

[82eye]

I'll try to upload my cylinder measurements. IIRC, max out-of-round is 0.03mm, and max conicity is 0.02mm. From what I measured (I will need to go back and double check), the maximum difference in measurements (front to back vs side to side) is 0.02mm, and the difference between just about every measurement top to bottom is 0.02mm. So is that considered too tapered?

how much time, energy, and cash are you willing to gamble on a questionable block at the outside of its tolerances? only you can answer that.

But wouldn't an overbore fix this?

that's not what an overbore is for. only you can decide. i'd find a good shop and take their recommendation.

What methods are these? I have looked over just about every forum post and couldn't find the answer.

try again. there are non hot tank methods of cleaning the block. again, you need a reputable shop to do it. there are loads of examples on the board of folk who had it done.

Is the best method to skim or try to straighten the head with tension first?

no.

I just get uneasy thinking about spending $$$ on valve guides/seats/valves when the clearances are still below the factory max spec. How much should I be looking to spend on that, reasonably.

don't bother to start if you are going to do it half-assed. all my machine work on the head and block was $1500cdn on the last build. you might do better as there are more options in the US.

final costs will be estimated after doing an autopsy on the current engine to determine it's needs.

[digger]

An overbore will fix your cylinder problems that is exactly one of the reasons why over size pistons exist.

You've come that far just skim the block lightly the small amount of material removal will not be a problem and the machine shop can also fix the relationship between deck and main tunnel to make it square/parallel etc.

Rods are reusable (unless you're building a high rpm race engine or stroker in which you'll want 24V rods or better) i would get them to check and address as required but definitely supply new rod bolts

The cam tunnel must be straight, so test how nicely/freely the cam rotates (should be no binding whatsoever otherwise your oil clearance will be essentially zero). Sometimes its best to straighten before skimming so the journals dont get chewed. If the cam doesn't move freely then it needs corrective action. The same if you dont skim it then when you torque the head it will deform the cam tunnel so might not be coaxial/linear and cause binding. There is a reason that almost every used head has damaged cam journals. It is not a pushord engine

The shop should be able to advise you on the valve train stuff and do the work as required. The exhaust side is often the issue. to me it doesn't make sense to err on the side of rectification if you're rebuilding with new pistons and so on just do it once and right. It is different if the head was done like 30k ago

[McGyver]

I would suggest boring the block for the 84.5mm pistons, they're the ones that are readily available.

Some shops hot tank, others put parts on a jet washer. It all depends on what cleaning solution they're using. I don't remember the specific metal and chemical concern, but look it up and ask them about it.

If you're going to pay for the work to be done, do it once. Replacing valve guides and cutting your valves/seats is pretty cheap. I would reuse the rods, but have them cut and re-bored, same as your main caps. Don't mix-match your main caps once the job it done! Have your crank polished. I would have the flywheel resurfaced and cut to light-weight it. If the clutch is good, you can re-use it, but it would be frustrating to pull the transmission in a few thousand miles because the used clutch was really worn. For flatness, go by the numbers in the Bentely, try to get everything as flat as possible (within reason). There is a recessed dimple on the bottom surface of the head, this is an indicator of how much can be removed before the head is out of tolerance and may kiss a valve. (bottom left circle in the pic below)

Here are my costs for reference. I think I paid a bit much for the bottom end work.

2021 - I bought a 280/274 regrind camshaft, ARP Head Studs, Main Studs, and Rod Bolts, Nuke Adjustable Cam Gear, HD Rocker Arms, ACL Race Main Bearings and Rod Bearings, Bottom End Gasket Set, and Head Gasket Set. This was about $2,006.

2022 - The head got jet washed, pressure tested, surfaced 0.005”, refaced valves, new valve guides and seals, and valve seats 3 angle cut. He had the m20b27 (81mm) crank magnafluxed and polished. The b27 (135mm) rods got cut, bored the big ends, and honed the small ends. I brought the head disassembled and without a cam, he put it together for me and tossed in a b25 cam he had laying around. This was about $884.

2024 - They hot tanked it (safe for the oil pump intermediate shaft bearing), magnafluxed the block, surfaced the block 0.075” (to restore compression), bored and honed the cylinders for new 84.5mm pistons with a torque plate (double over), cut and align honed the main caps, and CC’d the combustion chambers in the head. This cost about $1,195.

[dice2012]

Thanks for the advice everyone. I’m going to call the machine shop to ask for an estimate right now.
When you say the cam must turn freely, do you mean just turning it by the lobes? When it is in the head, I can turn it with the cam sprocket attached, but it is stiff. Can't turn it by hand without that attached.
Also, after checking the guide wear (valve play in the head) I found that most of the intake side has around 0.3-0.5mm play, which is under that 0.8mm spec from bentley. The exhaust side is about 0.55-0.6mm across the board. Should I assume that the guides are fine? Or just replace them anyways. I mean the head will need work regardless.
Trying to get this rebuild going so I can start to work on the other projects. I miss having a daily that is better on gas than my 4runner…

[TobyB]

Here's my 2c on the matter:

go talk to your machine shop in person, with the block and head in the trunk of your car.

You're not going to get a quote, as such, until they have all the parts on a cart and have measured them.
You CAN get price estimates up front 'yup, $65 a hole' or similar, so you'll have an idea of the scale of the cost-
once you have that, double it and you'll be fine.

Specifics: when boring, the shop will decide if the block needs decking.
All you do is ask that they take the minimum off that they can safely manage.
Depending on their machines, there will (or won't) be a minimum cut that gives a smooth finish.
This is also true for heads.

As to the head, you'll want to have it straightened just a bit
(the cam should turn freely enough that you don't need the sprocket)
and then cut the minimum that the shop can get it cut to get the surface straight.

If you're doing ANYTHING to the valves, change the guides. It just doesn't add that much cost,
and M20 guides are wear items. If you're getting the valves cut, changing the guides
(unless they're brand new) is just good economy.

Here's the other thing: your machinist knows more than you and I ever knew we didn't know.
So when you walk in, be clear that you're on a budget, but be humble. And while it's
fine to set project limits, if they say something isn't a good idea, then don't do it.
That applies to everything I've said, above, too- for example, if they say not to change
the guides since they'll set the clearances to what it's already at, don't have them change the guides!

t
can operate machines, is 100% not a machinist.

[dice2012]

The shop said that they can't straighten the head, and that nobody can straighten a head locally (and after looking around, I think this may be true). Is this something I can DIY at home before it gets resurfaced? I've seen stuff on straightening aluminum heads, but nothing with respect to e30 heads. After seeing a video of somebody assembling an m20 head, and how well the cam spun in that, I definitely am concerned by the cam journals binding.

I probably won't touch the valves or seats, but if the guides have to be replaced, then I will. Checked all of the guide wears again. Intake side had 0.6mm play in first cylinder, but 0.3mm play in the rest. Exhaust side had pretty much 0.55mm of play across the board. This is good, right? (Max spec in bentley is 0.8mm)

[digger]

The shop said that they can't straighten the head, and that nobody can straighten a head locally (and after looking around, I think this may be true). Is this something I can DIY at home before it gets resurfaced? I've seen stuff on straightening aluminum heads, but nothing with respect to e30 heads. After seeing a video of somebody assembling an m20 head, and how well the cam spun in that, I definitely am concerned by the cam journals binding.

I probably won't touch the valves or seats, but if the guides have to be replaced, then I will. Checked all of the guide wears again. Intake side had 0.6mm play in first cylinder, but 0.3mm play in the rest. Exhaust side had pretty much 0.55mm of play across the board. This is good, right? (Max spec in bentley is 0.8mm)

The process is buried in this thread.

https://www.speed-talk.com/forum/viewtopic.php?t=45868

[TobyB]

There's a definite science to straightening an aluminum head, and it
involves an oven that you've hotwired to get hotter AND a small
press that fits inside it. Take a look at UToob. I'm saving that for
when I want to burn the barn down, but it's certainly something I want to try...
...one of these days...

edit- digger, reading that thread, I'm not sure they know exactly what they're talking about.
Normalizing an aluminum casting takes more temperature than most kitchen ovens can do...
and I have an aversion to the 'puddling' method just because I've tried welding castings.
And it always creates more stress than it solves. But I'm just an idiot on the internet with
a healthy dose of skepticism. So until I do a dozen on my own, I'll stay firmly in my armchair.

t
Might put it in a press very, very, very carefully if he was feeling frisky.
Would only try puddling it if he didn't give a rodent's bottom about the head in question...

[dice2012]

Unfortunately I don’t have a TIG/Oxy acetylene torch setup.
Is it crazy to try bolting the head to my junk block with some shims under the high points until the cam spins freely, and then hit the head with a propane torch?? Not sure how I’d torque the head in my oven…

If this doesn’t work, is my only option left just resurfacing or buying a used head? Can the cam tunnels be align bored?

I’m really tempted to buy either a used head from someone, or get an AMC head from ECS. It sounds only a bit more expensive than getting everything done on the OEM head.

[digger]

There's a definite science to straightening an aluminum head, and it
involves an oven that you've hotwired to get hotter AND a small
press that fits inside it. Take a look at UToob. I'm saving that for
when I want to burn the barn down, but it's certainly something I want to try...
...one of these days...

edit- digger, reading that thread, I'm not sure they know exactly what they're talking about.
Normalizing an aluminum casting takes more temperature than most kitchen ovens can do...
and I have an aversion to the 'puddling' method just because I've tried welding castings.
And it always creates more stress than it solves. But I'm just an idiot on the internet with
a healthy dose of skepticism. So until I do a dozen on my own, I'll stay firmly in my armchair.

t
Might put it in a press very, very, very carefully if he was feeling frisky.
Would only try puddling it if he didn't give a rodent's bottom about the head in question...

it depends whos recommendation thats why i said buried. you just use strategic local heat as you progressively clamp it down to something flat. That thread was not correcting twist

Do you have an oxy-acetylene kit? If not, the tig will work, just an uglier finish. Once you have the head straight under tension, use the oxy to heat a small area somewhat below the tappet cover rail, and above a head bolt hole. You heat the aluminium to just before melting point, and then repeat for the remaining head bolt locations. I go in the same pattern I tighten the head bolts in. If there are more than four bolts per cylinder, I only heat the ones inbetween the cylinders. That way I can use the other locations if it needs to be done again. You do not get much of the bend out if you heat over a spot you have already done.

The higher up you can heat the head, generally the more effect it will have, though you will create high spots on the tappet cover rail. You can also use the tig to create a small pool in the same locations if you don't have an oxy-acetylene kit. Always try and put the same amount of heat in each location, and sometimes you might not need to heat every location depending on the amount of bend you have. You need to be careful about heating too close to a tappet bore as they will move around also.

[dice2012]

Before I could get a hot enough torch to attempt straightening the head, I found somebody nearby selling a good head for a good price. The cam turns freely, and the warp is about 0.0015" max, so I'm feeling pretty good about it. Apparently, it was off of a 40k mile car, and it looks so clean I believe it.

The setup I had going on, using some cut-up cans as shims, looked hilarious, and tightening the head bolts in the middle made it so the cam turned fine. For now, though, I'm gonna sideline the original head as a plan B in case something goes wrong with this new one. Would rather not wreck an oem casting due to my inexperience. Plus, I talked to a bunch of different shops and they all agreed I probably wouldn't be able to salvage the head with just resurfacing due to the design of the cam tunnels.

[dice2012]

The head is off at a cylinder head shop for vac check and resurfacing. Just talked to the machine shop I am going with for the bottom end, and I am about to pull the trigger on the parts cannon.

The shop insisted that for the price of rebuilding the rods (wrist pin bushings, big end cut), I might as well look at buying new/refurbed rods. Now I'm wondering if I should just go for forged rods/pistons, as I'm already spending the money and would value the strength for when I eventually put a turbo on this thing (not planning for crazy high boost though). Is it worth the extra $1k for pistons and $400 on rods? Or maybe m52 rods, though I feel that may run into the same problem with cost of rebuilding unless I buy them refurbished.

If so, what brands are good? Is Ireland Engineering good for engine internals? I see pretty good prices on their site, including refurbished connecting rods for $375

Is a torque plate needed for boring/honing? I've only seen a few references to it, and any google searches I make lead nowhere. The machinist said we'd need to find one to rent if it was required.

I'm most likely going to go with ARP studs for rods/head, sounds like a good investment. Not completely sold on the forged internals yet but it is certainly tempting.