Engine Life

[Lupine Lacuna]

How and why does and engine eventually die? Presumably they can always be repaired, it is more at what cost?

[Kickstart]

Hi

How long is a piece of string?

Wear of moving parts, failure of parts (which could include the crankcases), user abuse, lack of oil, under spec fuel, accident damage, over heating, poor attempts at tuning, etc.

Whether what is left is repairable will depend on what has gone wrong. Have an oil pump wear out resulting in very low oil pressure and you might well wrecked the crank, cams and head before you even get a oil pressure warning light. Cam chain snaps / jumps and you will likely land up with bent valves and wrecked valve guides along with possible damage to the pistons and big end bearings. Both would likely mean a 2nd hand engine is a lot cheaper than fixing what is left.

All the best

Keith
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[Howling TerrorOutOfOffice]

Whilst reading the thread 'CB500 Are they any good?'. I looked at wiki.

The 499 cc parallel twin DOHC engine was designed, according to Honda engineers, to last for 300,000 km. One bike was tested by Moto Revue from 1993 to 1996. Dismantled at 50,000 km (31,000 miles), the engine was in perfect condition. At 100,000 km (62,000 miles) only the distribution chain and the pistons were replaced, although, in the tester's opinion, it could have run with the original parts for longer with no problems.

It doesn't mention whether it did last 186,000 miles.
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[Babba]

Engines eventually die because they become obsolete or uneconomical to repair.

Besides mechanical friction wear, you also have the heating & cooling cycles a normal engine goes through.

Anything mechanical can be repaired, replaced or refurbished, but there comes a time when you just have to stop chucking effort & money at it.

How soon that happens is down to the initial design & build quality & also the life the engine has led.

[Wafer_Thin_Ham]

Normally the rest of the bike dies, or it's crashed before the engine gives up the ghost.

Lots of variables to consider of course, but the vast majority should be good for 100k +.
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[Cheeseybeaner]

[Howling TerrorOutOfOffice]

^^^Would allow for a thorough inspection. It was a test unit.
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[Kickstart]

[Cheeseybeaner]

[Andy_Pagin]

Well, my Landrover did about 350,000 miles before its first major rebuild.
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[Pete.]

Much lower revs though. Total piston cycle count will probably be similar to a 80-90k bike engine.
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[sickpup]

[Polarbear]

[sickpup]

[Howling TerrorOutOfOffice]

High mileage with lots of previous owners puts me off.
High mileage with a couple of owners not so bad in my eyes. Less likely to of skipped a service.

Nah I don't like high mileage bikes, they look tatty.
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[Teflon-Mike]

As Keith suggests; there are two ways an engine 'dies'.

It can just 'wear out'. Components rub together, gaps between them get bigger and bigger, until you dont have any compression in the cylinder, becouse it all leaks past the piston rings that are too loose in the bore, or out of valves that have worn so far that they dont close properly, or you have cams that wont open the valves properly, becouse the peak of the lobe has worn away, and the rocker pads has worn away and whats left barely takes up the gap before it moves the valve stem.

An engine 'wearing out' will tend to see a gradual drop off in performance, loosing power, throttle response and normally burning a lot of lubricating oil.

Then there are engines that 'Fail', and some part physically breaks and does mechanical damage to the engine.

Sometimes mechanical failure will be down to abuse, over reving the thing mashing down gears to fast, or after attempts to tune it.

Most often though, its when wear on a component sees it weakened to the point it cant take the loads placed on it.

Cam-Chains wearing slack, then snapping, as said, can cause consequental dammage, mashing postons and valves; a big end bearing failing from wear can see it 'jam' on the crank pin, snap at the little end and be 'thrown' smashing through the crank-case.

Anticipated 'wear' can usually be remidied by preventive maintenence; such as adjusting cam-chain tension, or adjusting tappets to close up clerances.

More advanced wear, usually requires 'reconditioning' and often component substitutions. So an engine that has worn out its cylinder bores, can be rebored to a larger size and new pistons fitted. Or a crank-shaft can be stripped and new bearings fitted to it.

Damage, usually can only be repaired by component replacement. So a bent valve and mashed piston from a snapped cam-chain would require the piston, valves and the broken cam-shaft replacing.

And engine that had 'thrown a rod', would obviousely require its broken rod replacing, but the crank case MIGHT be 'salvaged' the hole left by the broken rod, welded back up..... though in such a catastrophic failure such damage would probably damage so much of the rest of the engine, it wasn't worth repairing.

BUT yes, ultimately, almost ANY engine can be indefinitely repaired, given enough will and money.

Point of ecconomic repair, pretty much depends on the engine in question, and whether parts are ecconomically available, and what the value of the bike is worth.

There are a lot of one-off 'factory' racing bikes that are still used in classic competition, where there NEVER were proprietry off the shelf parts available for them, and the teams that maintain them, have to virtually hand craft every single component they need to keep them running... but the bikes are so valuable, or so important to thier owners, they deem the trouble worth while.

Fixing up old Honda CB125 'Super-Dreams', even with a fairly healthy supply of reasonably priced spares, often from china, on the other hand, I some-times question my sanity in going to the trouble!
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