Thread: BIG END BUSH REPAIR . IS IT POSSIBLE ??

Originally Posted by JDNSW

Many years ago (1963) I ran across a bloke driving round the gulf country in a Holden that seemed to be running very rough. I asked him about it, and he pointed out the piston and conrod on the back seat - it did a big end, so he pulled it out and kept oil pressure by wrapping the journal with a bit of a tin can and binding it with tie wire.

I have seen an engine which evidently had a similar problem - in the case I saw they packed a leather patch on the crankshaft where the missing big end went and held it in place with a jubilee clip around it. It worked this way on a farm for many years apparently.

Very few engines will let ya pull a piston and rod out from underneath as they have counter weights on the crank you cant get the piston past. Really old cars quite often dont have counter balancers on the cranl that will allow you to drop a puston out the bottom.

But a lot of stuff you could do back in the day wont work now as engines have much higher compression putting too much load for stuff like leather bearings

Not so much the compression as the high engine speeds and better breathing. Highest loads in any engine are from the power stroke and the reversal in direction twice per revolution. Compression load is much lower - remember that the pressure in the cylinder, and hence the load on the piston and big end is much less at the end of the compression stroke than it is a short time later when the fuel is burnt to increase the pressure for the power stroke.

Another factor that increases the load is the modern tendency to put turbochargers on everything - this enables more charge in the cylinder and as a result, increased combustion pressure.

Originally Posted by lyonsy

Very few engines will let ya pull a piston and rod out from underneath as they have counter weights on the crank you cant get the piston past. Really old cars quite often dont have counter balancers on the cranl that will allow you to drop a puston out the bottom.

But a lot of stuff you could do back in the day wont work now as engines have much higher compression putting too much load for stuff like leather bearings

To get the piston and rod assembly out of many pre-war engines you had to drop the bearing cap, push the rod and piston up the bore and remove the piston pin, take the piston off , and then remove the rod from underneath.

If you wish to test your ability as a fitter or engine builder, try putting an Offenhauser together having never seen one before and being presented with a crate of pieces stated to contain "three racing engines". These are beyond the ability of most A Grade Motor Mechanics. Like most aero engines.

Originally Posted by Bigbjorn

To get the piston and rod assembly out of many pre-war engines you had to drop the bearing cap, push the rod and piston up the bore and remove the piston pin, take the piston off , and then remove the rod from underneath.
.......

This applies to the Series 1 engine, and probably the six as well. To further complicate matters, you have to turn the assembly 90 degrees to access the gudgeon pin via the sloping top of the block and the exhaust port!

These are not a pre-war design, strictly. While the patents date to 1940 (obviously the design was earlier), production started post war, with the Landrover being the first to appear with them in 1948.

John

Well i would love to see ya pull a head off an offy. But then it was also designed to have the pistons taken out the bottom

I have a tool which lets you take a worn crank journal down to the next under size on most small engines with out pulling out the crank.
I dont think they are made now..........but still a great time and money saver if you know how to use the tool.
You just then fit a over size big end bearing and all is good again.

Originally Posted by lyonsy

Well i would love to see ya pull a head off an offy. But then it was also designed to have the pistons taken out the bottom

Head and block (called "case" in Offy talk) are cast in one. No separate head. They were methanol engines with compression ratios up to 16:1. No head gasket to fail. To remove pistons and rods one has to lift the block off the crankcase.

If you want a detailed study of these engines buy Ken Walton's most excellent near academic quality work "Offy, America's Greatest Racing Engine". This is the closest thing to an Offy workshop manual ever produced. Fred Offenhauser and later Lou Meyer and Dale Drake sold race engines to race teams, They assumed these guys didn't need to be told how to build and/or repair engines so no workshop manual

Edit- The book is available from the author direct. He lives just outside Kansas City. contact kenwalton@waltoncues .com