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MG Midget and Sprite Technical - I Think I Broke It (Part Two)

I started a thread a few weeks ago in which I reported that my engine had started smoking badly after a track day. Various causes were suggested (broken rings, stuck oil rings, valve stem seals, worn guides, etc.). I have just got around to dismantling the engine to investigate and here are some of my initial findings.

On removing the carbs/manifolds I found the inlet ports on the head were soaking in oil (some oil had even found its way into the carbs). As the car had been standing about a week since last running, would I be right in thinking that this is a clear indication of oil leaking from the head (valve seals, valve guides, a crack) into the ports? I can't see any other way for oil to get there - or is there?

I went on to remove the head to investigate further and found some odd marks on the block. I attach a photo showing the dark marks on the inlet/exhaust side of the block. The head gasket showed no signs of having blown between cylinders but I wonder if these marks indicate that the head was not seating properly (perhaps even leaking a small amount of oil from under the head). Bear in mind that the top of the block was machined flat about 2500 miles ago and was unmarked when I put the head on around 18 months ago. Any thoughts?

Chris H (1970 Midget 1275)

looks like it's blown between 2&3
What HG did you use and what over bore is it?
Onno K

Definatly looks like a HG failure ... the question is why

My guess the head studs didnt do there job because it appears all 8 push rod holes leaked between the HG and drained onto the intake manifold

Ither the head studs where worn out and couldnt hold the torque, the torque wrench has gone bad, or there was standing fluid in the stud head holes in the block or the stud where more then finger tightened into the block thus not allowing the stud head nuts to torque to a proper spec

At any rate the give away is the burnt carbon along the leftside of the head and the intake manifold covered in oil

Its almost like the head got hung up on that far side when being bolted down last time

Prop
Prop and the Blackhole Midget

<<it appears all 8 push rod holes leaked between the HG and drained onto the intake manifold>>

I'm not sure how that happens, Prop!
Dave O'Neill2

I should add that a compression test before dismantling gave equal readings (200 psi) across all four cylinders so I don't think the HG had blown between cylinders 2 & 3 and the engine ran well (just burned oil). There was a bit of carbon build up on the HG between 2 & 3 but the 'ring' was intact.

Onno - I used the black composite MG Metro Turbo HG (can't recall the part number). The over-bore is +60. The studs are competition studs used twice so should be OK. I'm not sure I understand Props comments that:

"there was standing fluid in the stud head holes in the block or the stud where more then finger tightened into the block thus not allowing the stud head nuts to torque to a proper spec"

Chris H (1970 Midget 1275)

What about my first point that oil in the inlet ports points to valve seals or guides? I inspected a couple of inlet valves and the seals were definitely shot (gone hard and opened up wider than the valves). The valve guides did not seem bad though. Can bad seals on their own be sufficient to allow significant leakage into the inlet manifold and hence the smoke?
Chris H (1970 Midget 1275)

Hey chris,

I just cant imagine this would be the case of a head issue, because the black damage is on the deck, between the deck and the head gasket

The blackened damage goes the entire length of the deck and centers around the pushrod holes

Thats why im blaming the cyl head studs. I just think that whole side wss not torqued to spec because it appears everything escaped that side

What I mean ... the cly head studs are not to be installed in the engine block more the finger tight...the clamping force comes from the nuts on top of the cly head, not in the block

Fluid in the stud holes... what I mean, if there is cleaning fluid, coolant or oil in the bottom of the holes that the cly head studs screw into, then that can give you a positive false reading during your torquing procedures


Do you have photo of the bottom of the cly head and the head gasket

Prop
Prop and the Blackhole Midget

Shot valve seals will definately cause the oil in the manifold - but at 2500 miles new stem seals shouldn't have work hardened. You need to look for the little circular spring - if it's missing it's possible you have sufficient lift from the cam + valve train to crush the top of the seals. In this situation the spring will ping off and be lost and the seal will get baggy.If it turns out to be a lift issue the height of the guides may need dropping to lower the height of the seal,and keep them out of harms way.
F Pollock

Checking the picture it looks like the stud holes have pulled up.This would explain the staining and possibly the gasket burning between 2 and 3. Be worth checking this with a straight edge.
F Pollock

Hi Chris what carb setup and do you have a breather upstream of the inlet manifold?

Peter
Peter Burgess Tuning

My thoughts:
For a 2500 mile engine you do have quite a lot of oily carbon build up in the cylinders - consistent with leaking valve guides. Do you use valve seals on all 8 valves, or just the inlets?

The fire rings appear to have remained intact other than between 2 and 3 where there's a bit of damage.
The fact that the fire ring contact areas are intact suggests that the marking across the block on the push-rod side is because the gasket has not clamped down fully, allowing combustion gasses to creep from between 2 & 3 between the block and the low pressure area of the gasket.

There are bright rings showing around the edges of the head stud holes. Suggesting perhaps that the block has "pulled up" as the bolts were tightened down. Is there a raised ring around the bolt holes when checked across the block with a straight edge? This would prevent the gasket from clamping fully down against the block. I can help to chamfer the edge of the hole slightly to avoid this happening.
Guy W

Can you put up a picture of BOTH sides of the head gasket?
Lawrence Slater

I am not familiar with the Metro Turbo gasket - but normally the reinforcers round the fire rings between the cylinders are placed on top of the gasket - they have clearly left marks on the block - are you sure the gasket was fitted the right way up?
Chris at Octarine Services

Thanks for all the comments so far.

Guy - the engine may have only done 2500 but the head was a lot older and IIRC the valve seals were not replaced (penny pinching) when the head was transferred from old engine to new. The valve seal I took off had a top hole much bigger that the valve stem despite the spring and would not stop anything. It also felt hard or at least not as flexible as I would expect. Clearly there is a use by date for these.

Peter
Carb is a HIF44 on a Titan manifold. The breather goes to the carb take off which is inboard of the carb body (usual HIF44 set up). I checked when running and smoking and there was no oil or smoke coming out of the breather pipe although there was slight (barely detectable) pressure coming out of the pipe.

Lawrence - I'll go resure the gasket from the bin and photo it later!

Chris - pretty sure it was the right way up but I will double check.

Chris
Chris H (1970 Midget 1275)

Just checked (1) gasket was on the right way up and (2) stud holes have not pulled up. Can't explain the bright ring around the stud holes other than they match the holes in the gasket.

I have forged 1.5 hi-lift rockers. They were fine when fitted but they now have quite badly pitted faces. I guess they would add to the normal sideways forces on the valve stems and that will not help oil leakage (and may even have worn the guides). I'm going to replace with roller rockers when I rebuild.

Gasket picture later (gasket recovered from bin but SWMBO is telling me it's teatime).

Chris
Chris H (1970 Midget 1275)

Here are pictures of the gasket as requested by Lawrence. Not sure what can be got from them. The gasket looks good apart from a little crustiness on the ring between 2 and 3.

Here top view:

Chris H (1970 Midget 1275)

And the view of the bottom of the gasket.

Chris H (1970 Midget 1275)

Is it crustiness or ring failure between 2&3

Prop
Prop and the Blackhole Midget

Hi Prop
There is burnt carbon on the ring directly between 2 & 3 but I don't think it has failed there.
Chris H (1970 Midget 1275)

Not quite sure if it's the light. But are you sure you have the top/bottom views marked properly? Can I see the imprint of writing on the block, and on the "top" view of the gasket, between the two pushrod holes?
Lawrence Slater

On the 1st photo by blowing it up really large it looks like its imprinted AF-470

Prop
Prop and the Blackhole Midget

I've been looking at the valve seals and I think F Pollock (Fergus) may have spotted a key issue. The seals show signs of mechanical damage and the only thing that could cause that (especially round damage at the top of the seal) would be contact with the bottom of the spring retainers - suggesting the valve guides need lowering a 1mm or so to give clearance.

Chris H (1970 Midget 1275)

You say 1,5 ratio rockers. Did you recalculate the valve lash accordingly? Other wise there might not heave bee enough play on the valve - rocker combo resulting in (over)heated exhaust valves.
Alex G Matla

This thread was discussed between 24/11/2013 and 06/12/2013

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