How to / DIY > Engines

Rebuilding ST1

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Farmer:
I'm in the process of rebuilding an ST1 that ran for a short time with low oil.  The two main crankshaft bearings show signs of damage, but the crank journals look good with no damage.  The crankshaft rod journal bearing has more damage and the crank has some discoloration.  I can't feel any damage to the crank surface, but I'm wondering if I need to do something to clean the surface of crank journal?  With the tools I have I can't accurately measure the crank to determine if it is out of round.  Thoughts?

Also, I have a parts and shop manual for the engine.  Is there an operator's manual available for this engine?

Thanks in advance for comments and advice.

cobbadog:
G'Day Farmer.
If you dont have the tools to acurately measure the journal then a pair of outside  calipers could do a good enough job. If you have a large enough spanner to be a snug fit try it on the journl in a few places. I would simply clean the journal with a length of fine emery paper not to remove any discolourisation but to clean it up ready for assembly. I would replace the main bearings because if you can see sings of wear then its time to  replace.
AS for a hand book / operators manual I dont know but if you do a Google search you may find one. Is there anything in particular you need to know about start ups etc?

ajaffa1:
Hi Farmer, I think the crank will be fine unless it already had a lot of wear in it, bearing shells break down without oil much faster than crankshafts. Did the engine seize? If it did the chances are that it was the aluminium piston seizing in the bore. The camshaft has brass/bronze bushes and should be ok, as should the governor mechanism.
I would take a good look at the condition of the small oil pump, it is situated under a plug in the bottom of the engine and driven off a lobe on the camshaft. It is a simple piston pump and could easily be damaged by lack of lubrication. No point in rebuilding an engine that will restart it`s life with low oil pressure.

Bob

Farmer:
Thanks for the comments.  I had some crocus cloth and I went ahead and lightly cleaned up the crank journal.  There was no roughness, but with a bit of careful effort, I was able to remove much of the discoloration from the bearing journal.  While at my local NAPA store, I rediscovered plastigage.  I checked the clearance and it's between .0055" and .006".  The maximum spec is .0055, but I think I'll go ahead with the rebuild (any concerns?).  Good comment re the oil pump.  I took it apart and found one of the o-rings was broken, but the clearances appeared good ok so I purchased the two required  o-rings along with a gasket kit for the engine.  I've also lapped in the valves as there was evidence of leakage.

As I've never been around one of these engines, and I'm replacing the piston and cylinder. I am looking for any break-in information as well as starting and operating information.  This unit has an electric starter so it should be easy to get it going.

Thanks for your comments
One last question, what is the oil reservoir and plunger that is screwed into the intake manifold?

ajaffa1:
Hi Farmer, I think the crankshaft should be OK, unless you are going to be relying on this engine as your primary mover. The crank could easily be reground, bearing shells come in under sizes of 10, 20, 30 & 40 thousandths of an inch. What condition is the little end bush in? Not a difficult/expensive replacement, some need reaming to size after fitting.
Diesel engines are a little different to petrol engines, when running them in it is essential to have a sizeable load on the engine or the bores will become glazed and you will not get good compression.
The plunger mechanism is exactly what it looks like: a syringe. You fill the reservoir with engine oil and push the plunger down, this oil then sits on top of the piston increasing the compression ratio for easier cold starting.
Starting these is relatively simple, especially with an electric start. Check the injector pump rack is fully open, bleed the fuel system at each point, there are little bleed screws on the fuel filter and etc. Work your way from the fuel tank to the injector pump, once you have fuel flowing from the top of the injector pump fit the high pressure pipe, do not do up the nut at the top where it fits onto the fuel injector, leave it slightly loose. Crank the engine over until you get fuel squirting out around the loose nut, now do it up. Crank the engine over a few times and it should start.

Good luck.

Bob

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