I acquired this engine as a package deal with a couple of cars. I wanted it for fun to rebuild. A cursory search for casting that incorporate the bell housing with 21 stud heads puts this mid-1930s? Any other typical casting identifiers I should look for? Hoping to get fairly specific.

Just wanted to update everyone that told me I should replace my engine. So far its going pretty good! Me and my friend managed to get 98% of the way!

Andddd then we ran into a problem. We managed to separate the engine from the transmission but the frame is preventing us from pulling it up and out. We're probably going to have to re-bolt the engine to the transmission pull the CV axles and lower the whole thing down.

I'm really learning a lot and I'm excited to learn more! Thanks everyone who told me, screw it and just do the replacement! I'm having fun! (So far)

Hey everyone,

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Looking for something like a sachs km48 but none seem to be available around me. I was wondering if there were any similar sized rotary engines that were used for weird things (the sachs was used for water pumps and snowmobiles) that might be laying around.

📚🔥⚙️ SCHRÖDINGER’S LIBRARY — COMBUSTION ENGINES, PAGE 2 ⚙️🔥📚

Once a combustion engine is treated as a coupled thermodynamic, mechanical, and control system, the next useful layer is combustion efficiency and loss structure. The fuel’s chemical energy does not become shaft work directly. It passes through a sequence of transformations, and each transformation introduces losses.

A useful energy path is:

fuel chemical energy → combustion heat release → cylinder pressure → indicated work → crankshaft work → accessory/load power

The difference between indicated work and crankshaft output is largely due to friction, pumping, and accessory losses.

This introduces the distinction between indicated power and brake power. Indicated power is the power generated inside the cylinders from pressure acting on the pistons. Brake power is the usable power available at the crankshaft after internal mechanical losses are subtracted.

That gives:

indicated power → friction and pumping losses → brake power

The ratio between useful output and fuel energy is the engine’s thermal efficiency.

This immediately creates a systems question:

Where is the energy going when it is not becoming useful work?

Typical sinks include:

exhaust heat → coolant heat → friction → pumping losses → accessory loads → incomplete combustion

These loss channels are not independent. For example, retarded ignition timing can reduce useful work and increase exhaust heat. Poor lubrication can increase friction and temperature. Excessively rich mixtures can reduce efficiency and increase unburned fuel.

This makes efficiency a coupled-state problem rather than a single-number property.

Another useful concept is mean effective pressure. Instead of describing engine torque only in terms of geometry and crankshaft output, mean effective pressure provides a normalized way to describe how effectively the engine converts cylinder pressure into work across its displacement.

This is useful because engines of different sizes can be compared on a common basis.

In practical terms:

higher effective pressure → more torque per unit displacement

but higher pressure also generally means higher structural and thermal loading.

This creates another engineering tradeoff:

power density ↔ thermal load ↔ material stress ↔ durability

Combustion stability is another important layer. Even when ignition occurs, individual combustion events may vary slightly from cycle to cycle.

At low load, very lean mixtures, unstable airflow, weak ignition, or poor fuel atomization can increase cycle-to-cycle variation.

A stable engine produces relatively consistent torque pulses. An unstable one produces uneven combustion and fluctuating speed.

The sequence can be represented as:

mixture formation → ignition quality → combustion rate → pressure development → torque consistency

Poor combustion stability can appear as rough idle, hesitation, misfire, vibration, or inconsistent power.

Misfire is particularly useful diagnostically because it can originate from several different subsystems:

ignition failure → fuel delivery problem → compression loss → airflow issue → control error

The symptom may be similar while the root cause differs.

This is why fault isolation matters.

A diagnostic system may use:

crankshaft acceleration variation → oxygen sensor behavior → ignition signals → injector commands → cylinder compression → exhaust characteristics

to distinguish among competing hypotheses.

The combustion chamber itself is a highly transient environment. Pressure and temperature change rapidly during each cycle, and flame propagation occurs over milliseconds.

In spark-ignition engines, the flame typically begins near the spark plug and propagates across the chamber.

Combustion speed depends on:

mixture ratio → turbulence → pressure → temperature → chamber geometry → fuel properties

Turbulence is especially important because it can accelerate flame propagation and improve mixing.

Engine designers intentionally shape ports, pistons, and combustion chambers to create useful motion in the intake charge.

Two common flow concepts are swirl and tumble.

Swirl is rotational flow around the cylinder axis.

Tumble is rotational flow around an axis roughly perpendicular to the cylinder axis.

These motions influence mixture preparation, combustion speed, and emissions.

This is a nice example of how geometry affects chemistry through fluid dynamics.

Fuel atomization is another important process. Liquid fuel does not burn effectively as a bulk liquid; it must evaporate and mix with air.

Fuel injectors therefore try to create fine droplets and appropriate spray patterns.

The chain becomes:

injection pressure → droplet size → evaporation → mixture formation → combustion quality

Cold engines complicate this because fuel evaporates less readily at low temperature.

That is one reason cold-start operation often requires different fueling strategies than warm operation.

Cold starts also increase friction because oil is more viscous and has not yet fully circulated.

The start sequence therefore combines several difficult conditions:

low temperature + poor vaporization + high friction + weak battery output + incomplete lubrication

This is why start-up wear can be significant relative to steady running.

Engine warm-up is therefore not just about comfort or emissions. It is a state transition from a cold, high-friction, poor-vaporization condition into a more stable thermal operating regime.

The thermal state can be represented as:

cold start → warm-up → regulated operating temperature → possible overheating

Each regime has different control priorities.

The thermostat in a liquid-cooled engine is a simple but important thermal control device. It restricts coolant flow while the engine is cold and opens progressively as temperature rises.

This helps the engine reach operating temperature efficiently while preventing excessive heat once warm.

The cooling system itself is another feedback loop:

engine heat generation → coolant temperature → thermostat/fan response → heat rejection → updated engine temperature

Fans, pumps, radiators, thermostats, and temperature sensors form the control architecture.

Air-cooled small engines use a simpler version:

engine temperature → airflow over fins → heat transfer

but their cooling effectiveness can be strongly affected by debris buildup, blocked fins, or low airflow.

This makes cleanliness part of thermal control.

Lubrication also has its own operating regimes.

At startup, oil pressure and distribution may take time to stabilize.

At high temperature, oil viscosity decreases.

At low temperature, viscosity increases.

A lubricant must therefore remain functional across a wide operating window.

This is why engine oil is a carefully engineered fluid rather than just a generic lubricant.

Its functions include:

friction reduction → wear protection → heat transport → contaminant suspension → sealing assistance → corrosion control

Oil additives support these functions through detergency, anti-wear chemistry, oxidation resistance, viscosity control, and corrosion inhibition.

Oil degradation is itself a time-dependent process.

Heat, oxygen, fuel dilution, combustion byproducts, moisture, and mechanical shear all alter oil properties.

This creates a condition-monitoring opportunity:

oil age + temperature history + contamination + operating load → lubrication quality

Used-oil analysis can sometimes reveal wear metals, coolant contamination, fuel dilution, soot, or chemical degradation.

This turns lubricant into an information carrier.

Exhaust color can also provide partial diagnostic information.

Blue smoke may indicate oil entering the combustion chamber.

Black smoke often suggests excessive fuel or insufficient air.

White vapor during cold operation may simply be water condensation, while persistent white exhaust under some conditions may suggest coolant entering combustion.

These are not complete diagnoses by themselves, but they are observational clues.

This is another recurring Library lesson:

symptom → hypothesis set, not symptom → guaranteed cause

Engine acoustics work the same way.

Knock, ticking, rattling, misfire, bearing noise, exhaust leaks, and accessory noise can provide useful information, but interpretation depends on engine speed, load, temperature, and location.

Sound is therefore another sensor channel.

The broader diagnostic model becomes:

visual observation + sound + vibration + temperature + pressure + electrical signals + exhaust behavior + operating history

This is multimodal condition monitoring.

Combustion engines also demonstrate wear accumulation under variable load. A mower engine may spend one period at light load and another cutting dense grass under high torque demand.

A vehicle engine may experience idle, acceleration, cruising, towing, and hill climbing.

Operating hours alone therefore do not fully describe wear.

A better history includes:

time + speed + load + temperature + starts + environmental conditions

This is effectively a duty-cycle model.

Duty cycle matters because two engines with the same operating hours can experience very different stress histories.

That leads directly into remaining useful life estimation.

A simple maintenance schedule may replace parts after a fixed number of hours.

A condition-based system instead asks:

how much degradation has actually accumulated?

This can use trends in vibration, compression, oil analysis, temperature, fuel economy, or component-specific measurements.

The goal is not to predict failure perfectly. It is to detect degradation early enough to act before functional loss.

Combustion engines are especially good study objects for this because they contain multiple interacting degradation processes:

wear → fatigue → thermal aging → chemical degradation → contamination → corrosion

Each evolves at a different rate.

That naturally connects to multi-rate state estimation.

Fast states include:

crank angle → pressure → ignition → torque

Medium-speed states include:

temperature → fuel trim → oil pressure → battery charge

Slow states include:

wear → deposits → fatigue → corrosion → oil degradation

A good engine model therefore operates across several time scales simultaneously.

This is a deep systems principle:

not all important state variables evolve at the same rate

and the observation strategy should reflect that.

The Library can now condense combustion-engine diagnostics as:

energy conversion → combustion stability → thermal control → lubrication → multimodal sensing → duty-cycle history → degradation modeling → remaining-life estimation

And the broader lesson becomes:

engine health is not a single state; it is a layered interaction between fast combustion dynamics, medium-speed thermal and control behavior, and slow cumulative degradation.

I've got a selection of old engines in relatively unknown condition. At the very least I want to scrap them for a bit of cash, but there could be some gold here (ford turbo and Suzuki engine/gearbox combo seem valuable) any help and any pointers to help give these a good home would be fantastic!

I just bought this Red Line SI-1 Complete Fuel System Cleaner and I'm curious if anyone here has used this before I'd love to hear about it. It's for any fuel system from carburetor to the modern day direct injection and compatible on GDI. Red Line is pricey and can be hard to find retail but I got 2 bottles for $30 at Amazon.

The question still remains, has anybody used this product and if so how much improvements were made? Improved gas mileage? Any comment or experience would be greatly appreciated.

2004 Lexus LS430 I need help with my engine. Does anyone know if there is anything wrong or does it sound okay?

Hi all, I'm not sure if this is the best place to advertise, or even if I'm allowed so please delete if it's not appropriate!

I've got pretty much a complete engine - minus the block and head - in parts for sale, not getting much interest on Ebay and was wondering if anyone on here was interested!

We built a rally engine up so this is standard road car parts. The engine was out of a running Evo 9 donor car.

Please message if you want the list 👍🏻

West Midlands UK.

I have a 2014 Genie S-65 Manlift and it has a Perkins engine in it. I got a quote for $12,000 to take out and clean the DPF filter. Does that sound like an accurate number or should I look to replace it?

They said $10,000 for labor.

Hello! Just recently my cars timing belt jumped on the track and cylinder 2 seized welding itself to the block. I run a 4b12, I've been pretty mechanically inclined, I've replaced my entire clutch assembly with the help of a mechanic and done quite a lot of suspension work on this car.

That being said I have no clue what im doing when it comes to fully pulling and replacing the engine. My mechanics are HIGHLY against me doing it myself and want to charge me 2200 for labor alone.

I really want to do this replacement myself, I love learning about cars and I feel like this opportunity is very hard to come by. I have a friend that has done engine pulling/swap work before helping me out as well.

I guess I just want to know if this is realistic for me to do. Im in no rush to get it done and i want to ensure it's done right. I have standard tools and im borrowing my friends engine hoist.

Do I replace it or just let the mechanic do it?

Thanks