Overthrown Crank ?

[Nige F]

as title - re a Saab engine - WTF ? can't find any info on t'net. It appears in an ad for a used Saab on eBay. Thanks

 

[Keithmac]

Over square?.

 

[Mursal]

Maybe a polite way of saying it has a hole in the side of the engine where the crank/con rod came through?
But just contact the seller, before you bid .........

 

[Burnerman]

The crankshaft throw is the distance between its centre line of the main bearings to the centre line of the big end journals so yes, its the stroke of the crank at the end of the day.
John

 

[Paintguy]

Beats me, and I've been working on cars for 35 years

Unless he means the crank has been modified / machined / changed to increase its throw, thus "overthrown". A bit like increasing the bore size would be called "overbored"

 

[Keithmac]

You'd normally say it's been stroked, maybe best off sending him a message.

If it's been stroked it will have custom con-rods/ pistons or both.

 

[Mottie]

As I've always understood it, the crank pin is reground off centre so that the piston will sit slightly higher in the cylinder if using standard con rods. Often the top of the piston will need machining if the compression is too high or if there is a chance of it hitting the valves. This will give the piston slightly more travel down the cylinder and increase the cubic capacity. Often done in conjunction with boring the cylinder out to its maximum permisssble wall thickness. Really only done in competition engines when you are trying to wring every last drop of power out of them.

 

[Paintguy]

As I've always understood it, the crank pin is reground off centre so that the piston will sit slightly higher in the cylinder if using standard con rods.

Yes, that's the process I was thinking of, but I've never heard it called "overthrown" before. As Keithmac says, normally you'd say stroked.

 

[Nige F]

Thanks guys ! Reground off centre makes sense. Had me well puzzled No intent of buying it, just looked as I reminisced about an old 900 I had once,

 

[Burnerman]

Fitted a new turbo and alternator to a 2002 SAAB a couple of years ago.....looked like a Vectra engine to me had to take one of the headlamps out to get there
When the engine started up, the turbo pipes visibly bulged - there must have been some pressure in there!
John

 

[Paintguy]

Fitted a new turbo and alternator to a 2002 SAAB a couple of years ago.....looked like a Vectra engine to me

Yep, really old SAABs used a Triumph based engine, but the more modern ones were mostly based on Vauxhall lumps.

Vectra rear suspension and stuff too I believe

 

[Keithmac]

GM bought Saab a fair while back iirc?.

 

[Paintguy]

Didn't seem to help though as they still went bankrupt.

I hear rumours that SAAB may return, but we'll see.

 

[DaveHerns]

Really, really old Saabs used the German Ford V4 engine. At least Saab reworked the Triumph Dolomite engine so the head gasket problems were cured.

 

[Burnerman]

I got to know the SAAB two stroke engine quite well.....hearing it in the distance it sounded to be doing the ton at least but when it appeared a snail could have blown it off
Remember the V4 lump too, if it was the one fitted to the original Transit - con rods shared the same crank pin and the head gaskets would pop if the sun came out
John