Engine Dilema - Perkins 4.236

[Tranona]

It is said that diesel engines like it better when they are worked hard, i.e. a smaller engine that has to be run at higher revs is likely to be more reliable than one that spends its working life at running at barely above tickover.

Not the case here. The 4 236 is exactly the right engine for the boat and unlike the higher revving smaller capacity engines it produces its power lower down. 1200rpm (out of its 2600) is around half power so it is properly loaded at cruising speed. More modern higher revving engines (3000-3600 range) usually produce 50% power at 65-70% revs, particularly if turbocharged as the equivalent HP Volvo and Yanmar models.

 

[Beneteau381]

Not the case here. The 4 236 is exactly the right engine for the boat and unlike the higher revving smaller capacity engines it produces its power lower down. 1200rpm (out of its 2600) is around half power so it is properly loaded at cruising speed. More modern higher revving engines (3000-3600 range) usually produce 50% power at 65-70% revs, particularly if turbocharged as the equivalent HP Volvo and Yanmar models.

I cut my teeth on Rolls Royce Eagle engines in Janus locos, they were hi speed, max revs iirc were 1800 rpm. My Cat 3306 gennies in Angola base camp were high speed as well. Ran at 1500 rpm for 50hz gennies and 1800 for 60hz

 

[Tremyporth]

Hi CanePazzo

Paper work inherited with my boat confirms that it was fitted from new in 1981 with a Perkins 4.236M (for marine) lowline engine, built by Perkins in Peterborough, then sent by them as a complete unit to Golden Arrow Marine, who supplied it to the boatbuilder. So if there is any remaining confusion I can confirm that Perkins did make a marine version of this prolific and successful engine. Later versions became called M90.

In addition, there was a significant number of “marinised” 4.236 engines, created by adding the marine heat exchangers, manifolds, etc to engines salvaged from sources such as written off road vehicles, tractors, JCBs etc. People like Mike Bellamy of Lancing Marine were able to supply all the necessary parts if you did not have your own defunct marine engine to cannibalise. The key to the origin of each individual engine lies in the engine number.

As has been written above, Perkins has been taken over by Caterpiller. I have been unable to discern any improvement in the supply of Perkins spare parts or production of a greater range of engines since that takeover. Perkins did not even bother to attend the “Seawork” show last June.

I overhauled the cylinder head and cooling system of my engine last year. I judged that to be worthwhile, not least because I do not charge myself for labour, but also because of the good mechanical condition of the engine, coupled with the potentially large amount of time and money which would be involved in replacing it with a different engine, ancilliaries, mountings etc.etc.

The calculations would be very different if you had to pay somebody else to undertake the contortions necessary to unseize bolts and remove components on the engine in situ. It is vastly quicker to take out the old engine and gearbox in one lump and replace with a new modern unit. That is what most boatyards would advise, I suspect. But it is a good engine. Easily maintained. Economical. No need for a laptop to diagnose problems. Because it was fitted in so many different land-based applications, the mechanical parts like pistons, cylinder liners, bearings, valves, water pump, fuel system etc. are all readily availble and not terribly expensive.

Where it gets more difficult is the marine cooling system. Not all parts are available now. As Fisherman wrote, you can replace heat exchangers with others of similar capacity. Mounting them remotely from the engine may even offer advantages of accessibility when servicing. Re-routing some of the pipework away from the rear of the raw water pump would greatly assist impellor changes.

The original design header tank and water cooled exhaust manifold have been unavailable for some time, although at a cost a modern combined alternative has been advertised. Another option is to find one of the makers of custom or sports car manifolds and exhaust systems, and get them to make a one off water cooled manifold in stainless steel. Expensive, but less than a new engine and gearbox. Some of the gaskets are not available any more either. But the materials are, and a competent fitter can make gaskets. But more labour costs perhaps. Incidentally to add to the lists of suppliers of parts, I can suggest Rollo Engineering, near the entrance to Portbury Docks, Bristol, and for custom-made gaskets, the always helpful Redruth firm:

https://www.ramgaskets.com



Best of luck with your transplant.

 

[coopec]

It is said that diesel engines like it better when they are worked hard, i.e. a smaller engine that has to be run at higher revs is likely to be more reliable than one that spends its working life at running at barely above tickover.

Yes, quite right.
It is important to have the right sized/pitch propeller fitted to get maximum thrust under load at 2550-3000 rpm.

"Operating diesel engines at light loads for extended periods of time can cause glazing to the cylinder bores. This occurs because poor combustion can lead to soot formation and unburnt fuel residue which clogs & gums up piston rings which causes the piston rings to not seal as well".29 Mar 2019

Generator Sets and Diesel Engine Glazing

 

[fisherman]

I never bothered to find out before, but 1 litre is 61 cu in, so the 6/354 is 5.8 lt, 4/236 is 3.87 lt, 4/154 (in a Bedford truck I had) is 2.525 lt, and the 4/108 is 1.77 lt.

The 1913-1934 Kelvin 'Poppet', pet/par was 50/60 hp, 4 cyl, 410 rpm, and 29 litres. Weighed 1.9 tons. 57 ins high, stick that under your companionway.
Probably enough grunt for a small coaster.

Kelvin Poppet Valve Engines

 

[PaulRainbow]

Yes, quite right.
It is important to have the right sized/pitch propeller fitted to get maximum thrust under load at 2550-3000 rpm.

You might want to rethink that.

 

[coopec]

You might want to rethink that.

I'm not sure what you are getting at. (RPM for a 4.236 too high? "Idle speed: 750 rpm, Rated speed: 2,000 rpm, Max. torque at 1,300 rpm )

When the propeller specialist "propped" my yacht he used a computer program similar to this (see link below) to work out the prop diameter/blades/pitch. (Forumites might like to play with this calculator)?

Free to use Propeller Sizing Calculators

 

[dankilb]

Our Beta 50 sees high load (in terms of torque) from 1200 rpm up. 1800 has us cruising at 7kts…

No need to rev the nuts off it to ensure a marine diesel is under load.

 

[westernman]

Our Beta 50 sees high load (in terms of torque) from 1200 rpm up. 1800 has us cruising at 7kts…

No need to rev the nuts off it to ensure a marine diesel is under load.

It is important not to overload it either. This is usually done by ensuring that the engine can reach its maximum RPM at maximum throttle.

If your engine cannot reach its max RPM it is overpropped. You need to be careful and ensure that once you have reach the maximum attainable RPM you back of the throttle so the RPMs drop a bit - say 200 RPM to ensure the engine is not being overfueled.

 

[Beneteau381]

Our Beta 50 sees high load (in terms of torque) from 1200 rpm up. 1800 has us cruising at 7kts…

No need to rev the nuts off it to ensure a marine diesel is under load.

Correct sir. People forget that the "throttle" only sets the revs, it doesnt address the load, the governor does that. So 1200 rpm is nominal, try to stall it by increasing the load and the governor pours more fuel in within limits. The issue of enough air going in is another side show.

 

[Tranona]

coopec

That is correct, but actually the starting point is the propeller and then working back through the shaft speed and the hp required to turn it. With a fixed pitch prop it is only efficient at one speed and the aim when sizing is to get that speed within typically 10% of the rated maximum rpm of the engine. The prop does not care what engine is providing the hp or at what speed the engine is running - the reduction box sets the shaft rpm.

 

[PaulRainbow]

I'm not sure what you are getting at. (RPM for a 4.236 too high? "Idle speed: 750 rpm, Rated speed: 2,000 rpm, Max. torque at 1,300 rpm )

When the propeller specialist "propped" my yacht he used a computer program similar to this (see link below) to work out the prop diameter/blades/pitch. (Forumites might like to play with this calculator)?

Free to use Propeller Sizing Calculators

"It is important to have the right sized/pitch propeller fitted to get maximum thrust under load at 2550-3000 rpm."

Those revs will be too high for most marine engines (OK, some modern ones will be OK at high RPM).

My Westerly ran for over 40 years at about 2000 RPM max, still going strong.

My current boat has a pair of turbo diesels that max out at 2500rpm, but run happily at much less.

 

[coopec]

Our Beta 50 sees high load (in terms of torque) from 1200 rpm up. 1800 has us cruising at 7kts…

No need to rev the nuts off it to ensure a marine diesel is under load.

Well you shouldn't run your motor without a load as it will glaze the cylinder.

Feb 2018 — Running a diesel engine at low loads for long periods causes the pressure inside the cylinders to drop, impeding proper combustion and leaving ...
Since diesel engines are not designed to function at a small fraction of their maximum load for extended periods, the best way to prevent glazing occurring is to avoid idling (or driving at particularly low revs) for extended periods, especially during the first few months of an engine's working life

https://sundsvallsboule.com/2018/02/02/glaze-runner-what-is-cylinder-glazing-and-how-can-i-prevent-it-happening-to-my-diesel-engine/

 

[fisherman]

I had a Ford mermaid turbo 6 cyl 188hp. Had the pump serviced and could not get above 1800 revs, out of 2600. The engineer hadn't known it was a turbo so had set the pump for naturally aspirated. On the phone he or Mermaid, can't remember which, told us how to adjust it, a nut inside the side cover, he said to unscrew it under load until we got the revs we were used to and a slight haze of smoke.
My Mermaid 135 would start to smoke just a bit when the air cleaner got gooey, unburnt fuel of course. Could have done with better engine room ventilation.

 

[Beneteau381]

Well you shouldn't run your motor without a load as it will glaze the cylinder.

Feb 2018 — Running a diesel engine at low loads for long periods causes the pressure inside the cylinders to drop, impeding proper combustion and leaving ...
Since diesel engines are not designed to function at a small fraction of their maximum load for extended periods, the best way to prevent glazing occurring is to avoid idling (or driving at particularly low revs) for extended periods, especially during the first few months of an engine's working life

https://sundsvallsboule.com/2018/02/02/glaze-runner-what-is-cylinder-glazing-and-how-can-i-prevent-it-happening-to-my-diesel-engine/

" causes the pressure inside the cylinders to drop, impeding proper combustion and leaving ..." Really? I suspect a bit of poor translation.

 

[Tranona]

Well you shouldn't run your motor without a load as it will glaze the cylinder.

Feb 2018 — Running a diesel engine at low loads for long periods causes the pressure inside the cylinders to drop, impeding proper combustion and leaving ...
Since diesel engines are not designed to function at a small fraction of their maximum load for extended periods, the best way to prevent glazing occurring is to avoid idling (or driving at particularly low revs) for extended periods, especially during the first few months of an engine's working life

https://sundsvallsboule.com/2018/02/02/glaze-runner-what-is-cylinder-glazing-and-how-can-i-prevent-it-happening-to-my-diesel-engine/

Lot of misunderstanding about the causes of bore glazing, but just to be clear it is not about running an engine under load at relatively low rpm, but running with little or no load, for example to charge batteries where the alternator does not put any real load on but needs the revs to provide the charge. Another scenario is unique to boats when using the engine to supplement sail power where because sail power is providing most of the speed there is less load being placed on the engine by the prop for a given propeller speed.

If the prop is correct for the engine it will happily run at half power which on modern high speed engines is typic ally 65-70% maximum revs - which is exactly what Yanmar recommends. Moat of their small engines max at 3600 (as do many Volvo and Beta) and normally would cruise at 2400rpm. Look at the power curves for this type of engine and you will see why they need to rev like that. Compare with low revving, usually larger engines such as the Perkins under discussion which in its different forms max at anywhere between 2000 and 2800 (I believe the M version is 2600) which produce more power at lower rpm so cruising revs would normally be around 50% maximum - so 1400rpm.

Generally speaking, overpropping is worse than light load running, usually evidenced by black smoke and sound of the engine labouring and new engine commissioning will require the engine to meet the recommended maximum revs range (3300-3600 on my new beta). This range is given because it is often impossible to hit it right as 1" of prop pitch is equivalent to roughly 250-300 rpm (depending on actual shaft speed). So when my last boat was commissioned by Volvo it achieved 3100 out of 3200. My current Beta is over propped and goes to 2900 (we know why) and the pitch will be reduced to raise the revs although we will do more trials before we decide exactly how much.

 

[jdc]

Bore glazing - a plea. Does anyone have decent articles on the cause and prevention in reasonably modern (eg Kubota of Yanmar) Diesel engines? I'd like to understand it (I've no axe to grind and no preconceived ideas, but a healthy skepticism of hearsay).

I haven't found many despite searching - the second one posted above by Coopec definitely doesn't meet my test of 'decent' being (i) hearsay/unscientific and (ii) about petrol engines on cars as far as I can tell - but academic papers seem few and far between and inconclusive. For instance one from the US military says that running diesel generators at low load (but high revs) for ages and ages (think all winter) does no harm, and another covering a problem on a fishing boat found the only effective thing was using 100% synthetic oil with very low (0.8%) SAPS, implying oil type is an important factor.

 

[westernman]

Bore glazing - a plea. Does anyone have decent articles on the cause and prevention in reasonably modern (eg Kubota of Yanmar) Diesel engines? I'd like to understand it (I've no axe to grind and no preconceived ideas, but a healthy skepticism of hearsay).

I haven't found many despite searching - the second one posted above by Coopec definitely doesn't meet my test of 'decent' being (i) hearsay/unscientific and (ii) about petrol engines on cars as far as I can tell - but academic papers seem few and far between and inconclusive. For instance one from the US military says that running diesel generators at low load (but high revs) for ages and ages (think all winter) does no harm, and another covering a problem on a fishing boat found the only effective thing was using 100% synthetic oil with very low (0.8%) SAPS, implying oil type is an important factor.

If you have not already seen this you might want to take a look:-

Bore glazing and polishing in diesel engines

 

[coopec]

Bore glazing - a plea. Does anyone have decent articles on the cause and prevention in reasonably modern (eg Kubota of Yanmar) Diesel engines? I'd like to understand it (I've no axe to grind and no preconceived ideas, but a healthy skepticism of hearsay).

I haven't found many despite searching - the second one posted above by Coopec definitely doesn't meet my test of 'decent' being (i) hearsay/unscientific and (ii) about petrol engines on cars as far as I can tell - but academic papers seem few and far between and inconclusive. For instance one from the US military says that running diesel generators at low load (but high revs) for ages and ages (think all winter) does no harm, and another covering a problem on a fishing boat found the only effective thing was using 100% synthetic oil with very low (0.8%) SAPS, implying oil type is an important factor.

Why not do a google on "Causes of bore glazing diesels" and take your pick!
I notice one there by Cox Engineering
Bore glazing and polishing in diesel engines [NOTE Westerman you beat me to it!]

When I've researched the subject I invariably find statements like
"This is engine damage caused to generators either through misuse or poor sizing. A diesel engine is designed to operate at above 60% of it’s maximum load and ideally closer to 75%."
"Glazing," the biggest maintenance issue with generators.

If the yacht is being motored at 3knts then the diesel motor is no doubt well below 60% of its maximum load?

Both my B-I-L s worked for Caterpillar (and are boaties) and they confirm the above.

 

[Tranona]

If the yacht is being motored at 3knts then the diesel motor is no doubt well below 60% of its maximum load?

This really is a non issue for sailboat motors. Most people if using their motor will load it well. a cruising speed of a 9-11m yacht with an engine in the 20-40hp range will cruise between 5-6.5 knots which will require 50%+ of maximum load and usually higher, particularly with smaller engines. The issue with generators is well known, but is not transferable to yacht use. As I suggested earlier the only situation where you might get long term light load running is using the engine to "top up" sailing speed, but this is not common.