Oil in cylinders after rebuild - MG-Rover.org Forums
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post #1 of 13 (permalink) Old 22-12-2016, 10:43 Thread Starter
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Oil in cylinders after rebuild

Hi, I am Ash, I live in NZ and I have a problem, I like MG's. That feels good to get off my chest.
I am actually going off my MG a little. I bought it to compete in a series called 2K Cup and also in the European Classic Series in NZ. The first motor came pre cooked so that came out pretty quickly and I was lucky enough to find another VVC motor from a frontal crashed MGF. Both motors are '96/97 so they have the same issues. The second engine already had a new head gasket and was apparently a good runner before the crash, I serviced the motor, put new belt, tensioner and water pump on before sticking the lump back in, all seemed fine until a few weeks later it ran a big end bearing during qualifying.
Once I stripped it down I realised how bad the internals were chocked up from lack of servicing, even the VVC plunger was caked in gunk inside the unit. I cleaned it all up so it was shiny as the day it was made and I put it back together.
The crank was too badly damaged to use so I used the crank and pistons from the first engine which had cooked, given that they were in good condition. I thought it best to keep the crank and pistons together and assumed that they would be OK in the good block of engine #2. I installed new pistons, gapped them and clocked them but once back together the rings would not seat and the oil was flooding the cylinders. I hadn't honed the liners as they looked OK, but I should have done that so, I pulled it back down and honed the liners, checked ring gaps and clocked, still OK. Popped it all back together and it still smokes like a coal plant. I can't get the rings to seat on the freshly honed liners.
I have used SAE 30 to help the running in process.
Has anyone done a rebuild and experienced a smoke screen from the car afterwards. I'm not talking puffs of smoke, I'm talking about enough smoke to get arrested.
I took the car out at dusk today to see if a few Kilometres of high revs would help, it didn't.
I do have a sump baffle in, has anyone experienced issues after installing a baffle/windage tray?
The pistons are really sucking up the oil but I don't see how so much oil is getting to the bottom of the pistons in the first place, its not like the crank touches the oil in the sump.
The head has been done and all stem seals were renewed as was every other gasket in there. It now has the MLS gasket with steel shim.
It did not smoke before the change of crank and pistons.
PVC and hoses are all OK too.
I am thinking of installing new liners and pistons to hopefully fix this issue, but that seems extreme when it could be something simple.

Sorry for the long story, I tried to keep it relevant to the issue.
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post #2 of 13 (permalink) Old 22-12-2016, 15:25
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From what you said, it's about the tolerance of, and between, pistons and liners. Have you compared the dimensions of the original pistons with the replacement pistons? Are the liners you are using round and in tolerance? Did you refit the rings in the same position and the same way up? If you change orientation or position of the rings it can lead to greater oil consumption. If you like the dimensions and match of the pistons and liners, you could try new rings. It can get expensive though...

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post #3 of 13 (permalink) Old 22-12-2016, 18:22
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Do I take it that you have fitted the pistons from one engine in the bores of the other?
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post #4 of 13 (permalink) Old 22-12-2016, 18:37 Thread Starter
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Both motors had done around 135,000kms and the pistons and bores were very close on both, in condition and size. We clocked the rings to factory spec so I expect that they are in the same position, although I didn't check that.

I have put new rings on, but I wonder if we should use the old pistons and see if that that works.
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post #5 of 13 (permalink) Old 22-12-2016, 21:25
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Barking, I've just re-read the op and I think you are correct, first time I read it I thought pistons and liners had been moved but that's not what is said. You could well be on to something there.

By the way NZMGF, awesome job! Would love to see some pics of your work in progress stuff if you can.
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post #6 of 13 (permalink) Old 22-12-2016, 22:10 Thread Starter
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Yes, I had one overheated motor and one with a run bearing, I took the crank and pistons from the overheated motor as they were in great condition, then transferred them into the engine with the run bearing as that hadn't overheated.
The head and block from the cooked engine is no good, the crank in the run engine was no good, so I combined them, but its not a perfect match. The liners are still in the block which had the run bearing, the pistons from the cooked motor. New rings and fresh hone but there must be too much piston clearance.

Hopefully this works for some photos














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post #7 of 13 (permalink) Old 23-12-2016, 05:51
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What material are you referencing to get the sizes, tolerances and orientation of the liners, pistons and rings?

Do you have the MGR manual?

From memory there are different sizes/grades of liners and pistons.


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post #8 of 13 (permalink) Old 23-12-2016, 10:09
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With new rings and honed liners there is only one way the oil can get past.

The ring grooves in the pistons must have much too large a tolerance.

The oil is getting in by going round Behind the rings.
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post #9 of 13 (permalink) Old 27-12-2016, 08:55
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Ahh the 2K cup... You should win the 1.6 to 1.8 litre class in a VVC powered MGF.

If you're in Christchurch, try Cashel Caravan. They used to wreck MGFs and a reasonably priced for second hand parts.

BTW I have a home made hydragas pump if you need to pump up your suspension
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post #10 of 13 (permalink) Old 10-01-2017, 20:11 Thread Starter
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So I have removed the head and re-honed the cylinders and check the ring gaps and clocked positioning, all seemed OK there and the piston to liner gap is well in spec, the liners look great although one needed re-seating after it came loose.
Put it all back together and the problem is still there. Must be the valve seals.
I removed the head again and found that the seals which came in the new gasket pack are a slightly different shape, feeling confident that new, correct seals would do the job, I cleaned the head again, checked the straightness again, lapped in the valves again and put it all back together. This hasn't helped, the cylinders are still getting oil in them.

The compression is still good, over 200psi on each cylinder, there is no mixing of the coolant and oil and there is no evidence that the oil is passing the head gasket. So I feel happy that we can eliminate the head, block and gasket as being an issue, unless it is badly cracked and not visible.
The good compression would lead me to believe that the new rings are OK but that could be a red herring.

Is there any chance that huge oil pressure could force oil past the valve seals even if they are good and tight? I don't know what the oil pressure is and I will be checking the oil pressure relief valve tonight but I don't think that will be the issue.

If I do new liners and pistons, is it essential to remove and skim the block?
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post #11 of 13 (permalink) Old 11-01-2017, 07:33
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Are you giving it time to bed in?
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post #12 of 13 (permalink) Old 11-01-2017, 11:59
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Are you sure it is oil entering the cylinders/being burnt off?

Perhaps it could be a cleaning agent you used on the head i.e. behind the valve heads?

What about the possibility it is coolant being burnt off, via the Inlet Manifold Gasket for example?

What happens to the oil and coolant levels after some running with the engine as it is?


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post #13 of 13 (permalink) Old 11-01-2017, 13:33
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And is the oil level correct and the cam breathers installed correctly. Not sure if there is a one way valve in them - there is on the turbo.
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