A procurement team sourcing cylinder liners for the first time often gets one instruction from engineering: “we need the liner for the 6BT, same as last time.” That’s usually not enough to get an accurate quote, and it’s the single most common reason an RFQ for a diesel engine cylinder liner comes back with the wrong price, the wrong grade, or a request for five more emails before a supplier can even start costing it.
We’ve already covered how to vet a supplier in an earlier piece on choosing a cylinder liner manufacturer. This one covers the other half of the problem: what to actually put in the request itself. If you’re in procurement rather than engineering, you don’t need to become a metallurgist to write a complete RFQ – you need to know exactly what to put on it, which two or three details are worth chasing down before you send anything at all, and where to get the answer if you don’t already have it.
Why an Incomplete RFQ Costs You More Than Time
An incomplete RFQ doesn’t just slow down one quote – it changes what gets quoted. Leave the material grade blank, or write only “cast iron,” and a manufacturer has to guess which standard and class you mean, or default to whatever they quote most often. Leave the tolerance unstated on a bore that has to seal against a piston ring, and you’ll get a price based on a generic casting tolerance that has nothing to do with how tight that bore actually needs to run. Suppliers who handle this kind of enquiry regularly report that missing information is the single biggest reason a firm quote takes weeks instead of days, and that a wrong assumption on material or tolerance can move a quoted price significantly once it’s corrected mid-programme.
None of this requires procurement to solve engineering problems alone. It requires knowing what to ask engineering for, what to pull off an old part or an OEM manual, and what to leave open and flag as “confirm with supplier” rather than guessing.
The Cylinder Liner RFQ Checklist
Thirteen fields cover the large majority of what a manufacturer needs to quote a diesel, automotive or industrial engine cylinder liner accurately the first time.
| Field | What to Specify | Why It Matters |
| Engine make, model & application | Exact engine make/model/displacement (e.g., Cummins 6BT 5.9, Perkins 1004-4) or a drawing/part number, plus whether it’s for OEM production, a rebuild kit, or industrial/agricultural equipment | Lets the manufacturer match a liner already in their standing range instead of quoting a from-scratch development |
| Liner type | Wet or dry — and if wet, whether it’s flanged, mid-stop, or top-stop | Wet and dry liners aren’t interchangeable specs; getting this wrong invalidates the rest of the RFQ |
| Material grade & standard | The exact standard and class (e.g., ASTM A48 Class 35, DIN GG25), not just “cast iron” | A grade left unstated gets quoted against whatever the supplier assumes, which may not match your engine’s duty cycle |
| Bore diameter & tolerance | Finished bore diameter with its tolerance band or fitment/interference-fit grade, not just a nominal size | The bore is the fit-critical dimension against the piston; a nominal size alone says nothing about how tight it has to hold |
| Length, OD & wall thickness | Full dimensions with tolerances, or a reference drawing/sample | Confirms machining stock and tooling suitability before quoting |
| Surface finish | Rk/Rpk/Rvk plateau-honing values if known, otherwise “OEM-equivalent finish” | A bare Ra figure under-specifies a running bore; naming the honing spec (or asking the supplier to propose it) avoids an early-wear surprise |
| Sealing details (wet liners) | O-ring groove count, width and depth, flange thickness, collar diameter | These dimensions decide whether the liner actually seals in your block — the most common gap in wet-liner RFQs |
| Hardness | Required hardness range (e.g., Brinell HB), if your application specifies one | Matters most for higher-load or high-RPM engines where a standard grade’s default hardness isn’t enough |
| Coating or surface treatment | State if a phosphate coating or anti-corrosion treatment is required, or confirm none is | Coating changes both process and cost; silence gets read as “no coating” |
| Quantity & delivery schedule | Trial order size, projected annual volume if known, one-off vs. release schedule | Tooling-cost amortisation and lead time both depend on whether this is 50 pieces once or 5,000 a year on repeat |
| Drawing format & units | 2D PDF with GD&T where it applies, 3D file if available, units stated explicitly (mm or inch) | Avoids a supplier assuming millimetres against a drawing dimensioned in inches, or the reverse |
| Inspection & documentation | Material certificate, first-article/PPAP level if applicable, per-lot or per-shipment inspection report | Sets the paperwork expectation before the quote, not after the first container ships |
| Incoterm & ship-to | The Incoterm you’re quoting against (EXW, FOB, CIF, DDP) and the port or address it applies to | The same piece price can look completely different depending on which costs are already included |
Getting the Bore and Fit Specification Right
Two different standards can apply to the same liner, and mixing them up is a common RFQ mistake. The raw casting – before machining – is toleranced under ISO 8062, a system of sixteen grades (CT1 to CT16) covering dimensional tolerance and machining allowance for as-cast metal parts. That standard governs the rough casting stock, not the finished, honed bore.
The bore itself, once it’s machined and plateau honed, needs its own limit dimension or fitment grade – a specific tolerance band, in microns or ten-thousandths of an inch, that matches how the liner seats against the piston or the engine block. If your own engineering team hasn’t specified this, the honest move is to say so on the RFQ and ask the supplier to propose it based on the engine’s duty cycle, rather than leaving the field blank and hoping a generic tolerance is close enough. Whether the liner is going into an automotive diesel, an agricultural tractor engine, or a continuous-duty industrial engine changes what “tight enough” actually means, since RPM and duty cycle differ a lot across those three. Surface finish is part of the same conversation: state Rk, Rpk and Rvk values if you have them, or ask the manufacturer to recommend a plateau-honing spec rather than just writing “honed.”
What a Wet Liner’s RFQ Needs That a Dry Liner’s Doesn’t
A wet liner sits in direct contact with coolant, sealed by O-rings in grooves cut into the liner or the block, so its RFQ needs groove count, groove width and depth, and ideally the O-ring compound – coolant compatibility matters more than most buyers expect – plus flange thickness and collar diameter, since those carry the clamping load from the head. Leave those off and a supplier can quote the bore and length correctly and still send you a liner that won’t seal.
A dry liner is pressed into an existing bore and relies on an interference fit with the surrounding metal rather than a sealed groove, so its RFQ instead needs the press-fit interference value (or the block bore it has to match) and wall thickness, since that’s what carries the structural load a wet liner’s flange would otherwise handle. Naming which type you need, up front, decides which of these two very different spec lists actually applies.
If You Don’t Have a Drawing
Not every RFQ starts with a drawing. If you’re replacing a liner from an existing engine, a physical sample is usually enough – a manufacturer with reverse-engineering capability can measure it on a coordinate measuring machine and confirm the grade on a spectrometer, then reconstruct the dimensions and tolerances from the part itself rather than a document. Failing that, the engine make, model and year, plus whichever OEM service manual bore specifications you can find, usually gets a supplier close enough to propose a spec back to you for confirmation.
What doesn’t help is guessing at a dimension you’re not sure of and presenting it as fact. If a field is genuinely unknown, say so – “confirm against sample” or “TBD, please advise” is a more useful RFQ entry than an invented number, because it tells the supplier exactly where to focus their own review rather than quoting confidently against a wrong assumption.
The Paperwork to Specify Up Front
Quality documentation belongs in the RFQ itself, not in a follow-up email after the quote’s already back. State whether you need a material certificate with each shipment, whether a first-article dimensional report is required before series production – and at what PPAP level, if you’re running a formal automotive approval process – and whether an inspection report should accompany every lot or just the initial sample run.
If you don’t know which level of documentation your programme actually requires, say what the part is for – an OEM engine build, a certified rebuild kit, a general industrial application — and let the supplier recommend a level, rather than defaulting to the heaviest paperwork package for a part that doesn’t need it.
The Commercial Details a Technical Spec Still Needs
A technically complete RFQ can still come back with a confusing quote if the commercial details are missing. State your expected quantity as clearly as you can – a one-off trial order of a hundred pieces is priced differently from a programme with an annual release of several thousand, even if the piece itself is identical, because tooling cost amortises differently across the two. If you don’t know your annual volume yet, say so and give a trial quantity instead of leaving the field blank.
Name the Incoterm you’re quoting against – EXW, FOB, CIF or DDP under Incoterms 2020 are the ones most commonly used in casting export – along with the port or address it applies to, since the same piece price means something different depending on how much freight, insurance and customs clearance is already built in. It also helps to flag whether you need a budgetary, ballpark number to build an internal case, or a firm quote you can act on immediately; asking for the wrong one wastes both sides’ time.
So, What Exactly Do I Need to Put on the RFQ?
Strip all of this back, and a workable diesel engine cylinder liner RFQ needs six things at minimum: what engine or part it’s for (a drawing, a sample, or the make and model), whether it’s wet or dry, a material grade – or an explicit request for the supplier to recommend one — the bore dimension and how tight it actually has to hold, your quantity and delivery schedule, and which documents you need back with it. Everything else in this guide sharpens those six answers; a supplier worth working with will ask the follow-up questions on whatever’s still open rather than silently guessing.
Send us what you have – a full drawing, a sample, or just the engine model and a rough quantity – and we’ll come back with the grade, the process, the tooling cost if any, and a sample schedule, flagging anything we need you to confirm rather than assuming it. You can see the range of wet and dry cylinder liners and air-water cooled blocks we already build against, which covers a large share of RFQs before any new tooling is even needed.
Frequently Asked Questions
What’s the difference between an RFQ and an RFI when sourcing cylinder liners?
An RFI (request for information) asks a supplier whether they can make something in general — capability, certifications, rough capacity – before you’ve committed to specifics. An RFQ (request for quotation) asks for an actual price and lead time against a defined part, so it needs the specification detail covered in this guide. If you’re still comparing whether a supplier can even do centrifugal casting or IATF 16949-level work, that’s an RFI question; once you have a drawing or sample in hand, you’re ready for an RFQ.
Do I need a 3D CAD file, or is a 2D drawing enough?
A dimensioned 2D drawing with tolerances and GD&T callouts is enough for most cylinder liner quotes, since it’s fundamentally a rotationally symmetric part. A 3D file (STEP or similar) helps when the geometry is more complex – a flanged wet liner with an unusual groove profile, for example – but it’s a supplement to a toleranced 2D drawing, not a replacement for one, since tolerances aren’t always fully captured in a solid model alone.
What if my drawing doesn’t specify a tolerance for the bore?
Don’t leave it blank and hope. Either ask your own engineering team for the intended fit against the piston, or tell the supplier what the bore has to do and let them propose a tolerance based on the engine’s application and duty cycle – a competent manufacturer would rather ask this question before quoting than guess and have to revise the price later.
How do I compare quotes from suppliers who made different assumptions?
Ask each supplier to state their assumptions in writing alongside the quote – the material grade they priced against, the tolerance they assumed, and what documentation is included. Two quotes that look far apart on price are often quoting two different specifications, not two different levels of efficiency, and the gap usually closes once both suppliers are pricing the same actual part.
Should I request IATF 16949 or ISO certification in the RFQ itself?
Yes, if it matters to your programme – state it as a requirement rather than assuming every casting supplier holds it. IATF 16949 is specifically an automotive-industry standard and not every foundry carries it, so naming it upfront filters out suppliers who can’t meet it before you’ve invested time in a quote comparison.
What quantity should I put on an RFQ if I don’t know my annual volume yet?
Give a trial order quantity and say plainly that annual volume is still unknown – that’s a normal and useful answer. A supplier can quote a trial batch on its own terms and separately indicate how pricing would change at higher volumes, which is more useful than guessing at a number that turns out to be wrong.
Do I need to specify Incoterms on the RFQ, or can that wait until after quoting?
Put it on the RFQ. A quote priced EXW and a quote priced CIF can look very different on paper for the same part, and comparing them without knowing which Incoterm each one assumed is comparing two different things. Stating your preferred term upfront – or asking for the price under two or three common terms – keeps the comparison honest.
What documentation should arrive with the shipment versus be agreed at RFQ stage?
Agree the documentation package – material certificate, first-article report, per-lot inspection reports — at RFQ stage, so it’s priced in and expected by both sides. What arrives with the shipment should simply be that same agreed package, not a fresh negotiation after the goods are already on the water.
Can I send an RFQ with just a sample and no drawing at all?
Yes, this is common for replacement and aftermarket sourcing. A manufacturer with reverse-engineering capability can measure the sample and confirm material by spectrometer, then propose a full specification back to you for sign-off before anything is tooled or produced.
How long should a complete RFQ take to get a firm quote back?
It varies by supplier and part complexity, but a genuinely complete RFQ – drawing or sample, material, tolerance, quantity, documentation and commercial terms all stated — should move noticeably faster than one missing several of those fields, since the supplier isn’t stuck sending clarification emails before they can even start costing it.
Should procurement or engineering own the RFQ for a technical part like this?
In practice, both – procurement usually owns the commercial fields (quantity, schedule, Incoterm, budgetary vs firm quote) and needs engineering’s input on the technical fields (grade, tolerance, documentation level) rather than guessing at them alone. This guide is written so a procurement lead can gather that input efficiently, even without a metallurgy background, rather than having to become one.
Send Us What You Have
You don’t need a complete technical package before reaching out – send what you have, mark the rest “TBD,” and we’ll tell you what’s missing and what we can propose ourselves. Reach our team through the contact page with a drawing, a sample, or just an engine model and a rough quantity, or browse our cylinder liner and cooled block range first to see what’s already tooled and ready to quote fast.
About the Author
This article was written by the Esteem Auto team – the same engineers and quality staff who review incoming RFQs and first-article samples at our plant in Rajkot, India, every week. Esteem Auto Limited has manufactured cylinder liners, cylinder sleeves, air and water cooled blocks and custom castings since 1980, under an IATF 16949:2016, ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018 certified quality system, supplying OEMs, industrial buyers and aftermarket distributors in more than 50 countries. Send us your own RFQ, complete or not, through the contact page and we’ll tell you exactly what we still need.
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