92 replies to this topic

[camelotr]

Greetings Fellows!

I have a very nasty problem, and would like to ask Your help.

I have just rebuilt a 1275GT engine, and it is burning a LOT of oil. I will post pictures to let You see the depht of the problem.

The cranc was cracked between the cyl no2 and 3, thus it was velded and the bores sleeved back to std size. Pison-bore clearance: 0.06mms, ring clearance in grooves 0.05-0.06mms, ring gaps comp: 0.3, oil1: 0.25, oil2: 0.35. Cranc and head skimmed. Head rebuilt using brand new followers, valves. Oil seals on inlets.

Oil presure perfect hot and cold, at idle or reved. Engine is running smooth and fine. Willing to rev. No oil in water or water in oil. Compression tester shows 15-16 psi.

Crancase vent on clutch cover and valve cover, but not connected to inlet manifold. No gas on valve cover, some at clutch housing vent.

Smoking starts HOT. When cold it is not smoking.

Engine ran about 2-3 hours.

Tried yet without success:
- replacing head
- replacing oil (different types, brands 20/50-15/40)
- bypassing mechanic fuel pump
- using different head gasket


Please help a suffering mini nut...

[camelotr]

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[rotman1380]

looking at your pictures i would say its more than likely a cyl head problem, its unlikely that all four cyls (pistons) are going to burn that amount of oil. you say that you have replaced all the valves, are they the right ones ie; stem diameter, or is it possible that the guides are damaged in some way, though its unlikely that all four cyls would have the same prob if this was the case.
its gotta be worth checking before you start stripping the bottom half.
what a sickener!!
good luck.

[camelotr]

Unfrounatly the valve guides and valve-guide clearance were checked and rechecked.

I have replaced the cylinder head with another reconditioned unit and tried an old also. No difference.

I have recently striped the engine 3 times checked and rechecked again. All measurements look within tolerances.

[minidaves]

thats a lot of oil, and start with the simple things so take the head apart and check for tollerance (i dont think its that), if all good, try a oil drop on top of the pistons anout 100mlss or so and see how long it takes to disapear.

dave

[camelotr]

What kind of oil shell I use? Engine oil or diesel?

[mk3 Cooper S]

You need to perform a leakdown / comppession test to determine if it is the pistons / bores.

How much running has it done?

What type of oil ar you using to run it in?

[camelotr]

I have used first a low quality 15W40 for the first 5 minutes to run the engine hot and wash the engine inside.

Then removed the oil and replaced with medium quality mineral base 20W50. As I had opurtunity to change the oil a couple of times, I have always used different brand of oil. Always 15W40 or 20W50 all mineral base.

The engine had about 3-4 hours running.

[camelotr]

No leakdown test performed yet.
But the compression is fine (15-16 psi). Engine starts, runs and stops fine.

[mk3 Cooper S]

I think you need to compression test it.

Did you build it / fit the pistons into the bores?

[camelotr]

First time the shortblock was assembled by the mashine shop - a seal of warranty.
But I have dismantled the engine a few times. Even fitted new piston rings.

[rotman1380]

Unfrounatly the valve guides and valve-guide clearance were checked and rechecked.

I have replaced the cylinder head with another reconditioned unit and tried an old also. No difference.

I have recently striped the engine 3 times checked and rechecked again. All measurements look within tolerances.

rules that out then!
does the engine not smoke at all from cold?,if it really is only when its hot then (obviously) its a expansion problem, are the pistons and liners compatable? is it worth contacting the sleeve/piston suppliers, in case they have had this problem in the past?, is there ther some weird and wonderful running in procedure?.
i know im answering with questions, but you seem to of thought of/ or checked everything!

[Guess-Works.com]

Were the bores honed ?

As they look VERY shiney on the photo's, after only 3 hours running I would expect to still see fresh honing marks....

[rotman1380]

Unfrounatly the valve guides and valve-guide clearance were checked and rechecked.

I have replaced the cylinder head with another reconditioned unit and tried an old also. No difference.

I have recently striped the engine 3 times checked and rechecked again. All measurements look within tolerances.

rules that out then!
does the engine not smoke at all from cold?,if it really is only when its hot then (obviously) its a expansion problem, are the pistons and liners compatable? is it worth contacting the sleeve/piston suppliers, in case they have had this problem in the past?, is there ther some weird and wonderful running in procedure?.
i know im answering with questions, but you seem to of thought of/ or checked everything!

just thought, bores look awfully shiney for a engine thats done so little,if they are too shiney the new rings wont bed in properly causing your problem,could be worth glaze busting the bores.

[The Matt]

Yup, they look glazed, could just be the photo though?

I dunno, no signs of honing marks, which is odd.