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MG Midget and Sprite Technical - 76 1500 head gasket

hey, just pulled head off 1976 midget, coolant getting into oil found 2 middle cylinders with coolant but could not find no tell tale sighn of gasket failure or cracked head any take on the subject.
c.e.s. Charles Starke

Hi Charles,

If you ever get an answer to your thread could you let me know. I've a similiar problem but I have not pulled the head off yet. Cross contamination. The car ran fine on the way home last time. Came to change the coolent before a classic track night an low and behold.

Rgds
Neil
Navigator

There are two styles of gasket for the 1500. One is for flat topped blocks, the other has an extra thickness fire ring on one side, designed to sit in the groove around each bore. Maybe you have the wrong type of gasket fitted, so it has "failed" without appearing to have done so.
Deborah will know.

Guy
Guy Weller

Guy I think you are confusing the 1500 with the earlier 1300 blocks.


1300 blocks to serial number FH25000E were flat topped like the earlier small cranked 1300's and the 1147's.

1300 blocks from serial number FH25001E had recessed bores.

ALL 1500's have recessed bores.

I'd suggest checking the head isn't warped - good straight edge + feeler gauges.

Failing that, if it's not the gasket it's likely you have a cracked block or head.
Deborah Evans

As Deborah say's they're ALL recessed bores on a 1500 engine. I asked this not so long back.

IIRC Deborah, you said you machine the block to do away with the recesses and fit a "normal" 1300 gasket?
D Tetley

OK, I got that wrong so sorry for wrong advice - or rather, suggestion.

At least I got it partly wrong. When I had my 1500 I blew the head gasket whilst on a touring holiday in Scotland. I got a new gasket sent up from Glasgow and fitted it whilst staying at a camp site. On re-starting the car it blew again with 100 yards. When I stripped it I found that the gasket didn't have the proper offset fire ring to match the recessed 1500 block. Maybe it was for a different (non MG 1500) version of the triumph engine. I ordered a correct gasket with the fire rings and it was fine with that. So my conclusion was that there somewhere out there is a 1500 version without the recessed block. Either that or it was a rogue gasket of some sort.

Guy
Guy Weller

Guy,

The recessed bore of the Triumph 1500 engine is a problem in that it limits overboring to 20 thou.

Why BL did this is a mystery to me - they claimed it gave better fire ring sealing but there had (in my experience) never been a problem with the non recessed bore blocks.

I think they did it to bring the 4-pot motors in line with the MKII 6-pots in the same way that they increased the journal sizes in line with those of the 6-pots.

Additionally on tuned motors the recessed bore can act as an initiator for detonation.

Accordingly (as Mr Tetley correctly recalls), what I do when rebuilding these motors is deck the block flat, trial build and deck the pistons.

I then use the earlier style 1300 gasket (in the old days I would use a copper/asbestos gasket but these are about as rare as rocking horse droppings - they were rare 20 years ago) - I only use Payen gaskets now.

As you experienced, if you use a non recessed bore gasket (ie an early one) on a recessed bore it will blow in about the square root of F all time.

Conversely, were you to use a recessed bore gasket on a flat deck block then you'd have fluids gushing out the side of the motor between head and block (not just water in the cylinders). This would become apparent as soon as you filled the coolant system prior to first start up.

The confusion arises because the bore of the 1500 motor is the same as that of both the small crank 1300's and later large crank 1300's.

The difference in the 1500 is the stroke and the design of the webbing inside the block between the bores.
Deborah Evans

I guess what I was supplied with first time was a 1300 gasket in error. It certainly didn't last long!
Guy Weller

Two years ago I had a customer who decided to change his own busted valve spring, and dropped the valve down hole.
Then called me!
Cleaned it up, put it together with correct gasket, retorqued everything when hot, drove about 1/4 mile and blew all the water out.
Turned out that #4 had been sleeved (more than 20 years ago) and the sleeve was set too far down, so they filled it with epoxy, which looked just like CI on normal cleanup, except some of it scraped off in cleanup. Measurement and magnification showed the problem, cleaned off the rest of epoxy. There was a bevel around the OD of the sleeve as well as the depth problem.
As an emergency (IE cheap!) fix, I put a ring of copper wire around the counterbore in the groove formed by the bevel on the sleeve, and screwed it together - been fine ever since.
I'm convinced the counterbore scheme resulted when the last brain cell at Triumph died. The only gasket problem they ever had before this abortion was the oil feed at the LR corner. And I suppose it was practice for the Stag/Saab/TR7 cyl head fiasco.
FRM
FR Millmore

My erroneous diversion onto gasket failure, recessed and flat topped bores isn't really helping Charles. I think the conclusion to that particular red herring is that if a wrong gasket with the normal flush fire rings had been fitted then it would have blown in a very short space of time anyway so it doesn't sound like the problem.

If there is water in the oil and in 2 cylinders, and assuming that you drained the cooling level well down below the top of the block before you released the head, then there are only 3 possibilities that I can think of.

Leaking head gasket - not always very obvious. It may not have actually ruptured but look for water staining on the head and block surfaces. Check head with straight edge; it may need skimming.

Cracked head - crack may only open up when hot so look very closely or get it magnaflux tested.

Cracked bore - may also only open up when hot and could just look like a scratch on the bore. But would this cause water to fill 2 cylinders?

Hope it turns out to be the first of those! Good luck!

Guy
Guy Weller

This thread was discussed between 01/06/2009 and 16/06/2009

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