17 replies to this topic

[Kip123]

Hi ,if the timing chain breaks on the 1275cc cooper engine,would the pistons hit the valves?

[bpirie1000]

The general rule is yes. How did the chain snap. Usually stretch first causing poor driving..

All engines are about the ' right time bang..'.

[Spider]

With standard parts (cam and rockers) no, however, depending in the actual cam angle when the chain breaks, the Rod Big Ends may foul on a Cam lobe.

[absx2]

Interesting to know as I never thought about the crank touching.

 

I wonder if the OP is just asking a hypothetical question as for such a small and weak by modern standards part I don`t recall one ever breaking but no doubt they can and do I suppose.

 

I would still trust them over the modern stuff with the " death rattle " and self destructing cam belts immersed in oil 

[sledgehammer]

After all these years , it is likely to be a non std cooper 1275

so may have head skimmed , different valves ,  pistons ,  cam , rocker gear ,

 

head gasket , even valve clearance will make a difference .

 

At idle - probably no kissing

 

at 7000 rpm down hill - probably yes . 

 

also a new cam with a higher lift lobe , cut from a blank , will probably hit the con rod's ...

high lift cams cut from old cams should be smaller than std , so should miss (in theory).

also rockers with different ratio's from standard , may allow valve to kiss the piston

All the above is in theory 

Back in the day I worked on several Pinto's 2.0 - non interference with snapped belts .

 

pistons hit the valves - engines were being ragged to death at the time , cam fingers snapped as well

 

I think a series cam chains snapping is very rare - usually just very noisy 

 

but I have seen a tensioner break up which will cause problems

[gazza82]

 

Back in the day I worked on several Pinto's 2.0 - non interference with snapped belts .
 
pistons hit the valves - engines were being ragged to death at the time , cam fingers

Lost a belt on my 1.6 Pinto on M4 ... no internal damage but it was the low compression "company car" version. New belt and started first time.

My 2.0 TSpark Alfa was a different matter. Turned ignition, spun up engine and awful noise. Several bent valves - one so bent they had to snap it to remove it, damaged guides .. and all because a tensioner seized and stripped section of belt teeth. I have the belt and bend bits to remind me to get belts replaced regularly! One year one from rebuild big end went .. the impact from valves on piston squashed a bearing shell.


I've not heard of an A-series chain snapping ... a crankshaft yes!

[mab01uk]

BMW had a lot of cam chains stretch and/or the chain tensioners break up and self destruct the engines in recent years. Even worse was the 'new' design of engine had the cam chain at the rear of the engine which means removal of engine or gearbox to replace it. Depending on the value of the car some were uneconomic to repair outside of warranty....

[coopertaz]

these chains also snap without warning, happened to a work collegue as he was leaving after a night shift no noise prior to it luckily close to workplace so car was recovered. Never heard of a mini one going though they tend to make so much noise when stretched you would not drive it

[Shooter63]

BMW had a lot of cam chains stretch and/or the chain tensioners break up and self destruct the engines in recent years. Even worse was the 'new' design of engine had the cam chain at the rear of the engine which means removal of engine or gearbox to replace it. Depending on the value of the car some were uneconomic to repair outside of warranty....

The BMW chain problem is mainly due to the stupid service intervals BMW state, you cannot expect a high power turbocharged oil burner to go 16k between oil changes, Jaguars service intervals are even longer hence those engines letting go at ridiculous low mileages, throw in the insane Ford wet belt fiasco and it makes you wonder where it all went wrong. My Mk1 still has the original engine, no doubt fed all sorts of weird and wonderful fluids over the years yet still rattles along and probably would for plenty of years to come. To change the timing chain is a half day job max. Advancement isn't all it made out to be.

Shooter

[DeadSquare]

Does any one know how long a stroke crank could be cut if the cam shaft was replaced with a 3/8" shaft to drive the oil pump, and a BMW twincam conversion ?

[Shooter63]

Does any one know how long a stroke crank could be cut if the cam shaft was replaced with a 3/8" shaft to drive the oil pump, and a BMW twincam conversion ?

If you grind/turn the lobes off the camshaft to turn it into a plain jack shaft, there is no need to time the camshaft in, I'm sure you can get an 86mm to fit. A warning camshafts are HARD!!! unless you have an industrial size lathe it's slow going, ask me how I know.

Shooter

[DeadSquare]

 

Does any one know how long a stroke crank could be cut if the cam shaft was replaced with a 3/8" shaft to drive the oil pump, and a BMW twincam conversion ?

If you grind/turn the lobes off the camshaft to turn it into a plain jack shaft, there is no need to time the camshaft in, I'm sure you can get an 86mm to fit. A warning camshafts are HARD!!! unless you have an industrial size lathe it's slow going, ask me how I know.

Shooter

 

88.3MM would be nice, it would make 1,498cc with 73.5MM pistons.

 

I know what you mean about HARD.  I'm told that the way to do it is, slicing the lobes with an angle-grinder and then rounding the shaft off on a grindstone.

[Shooter63]

Does any one know how long a stroke crank could be cut if the cam shaft was replaced with a 3/8" shaft to drive the oil pump, and a BMW twincam conversion ?

If you grind/turn the lobes off the camshaft to turn it into a plain jack shaft, there is no need to time the camshaft in, I'm sure you can get an 86mm to fit. A warning camshafts are HARD!!! unless you have an industrial size lathe it's slow going, ask me how I know.

Shooter

88.3MM would be nice, it would make 1,498cc with 73.5MM pistons.
 
I know what you mean about HARD.  I'm told that the way to do it is, slicing the lobes with an angle-grinder and then rounding the shaft off on a grindstone.

I took the lobes off with an angry grinder, then set the camshaft up between centres for the final finish, but it is slow going, my lathe is a Harrison M250 and it really didn't like it, fine cuts and slow speed and a very fine feed were the order of the day, if I remember correctly I done 4 or 5 tips. In all honesty if you were going with that type of spec I would take a block, gearbox and transfer case to KAD and pay them some money and later pick up a complete finished power unit.

Shooter

[1968andyf]

The Ripspeed rally cross mini ran a 91mm crank with 74.7mm pistons giving 1598 to ru in the up to 1600 class, would imagine regular engine changes with that spec

[viz139]

Customer of mind broke an A series chain and it snapped the bottom sprocket in two. New chain, sprocket and cover and it was good to go.