Engine odd noise

[vibrodolly]

Have noticed a very odd new noise.

Imagine a really loud pinking type noise upon acceleration. It is hard (ish) to start and sluggish.
Only about 70% of power.

Tried disconnecting spark plug to see what cylinder it might be. 3 and 4 make little or no difference to overall power.
Valves are good. Head is 3000 miles. Have retimed valves. All push rods in place. No broken springs. What I can see is ok, yet this noise is bad. Don't notice it on idle, but much less revs on idle and will usually stop after 5 seconds.

Crank shaft? broken cracked con rod? Not really sure about the bottom of the engine workings.

It is a 1958 948cc 2 door saloon.

If engine knackered, possible solution is fitting a known good 1098 engine I have. I have the gear box too.

My questions...
What might be wrong with the current engine?
Can I straight swap a 948 engine out 1098 in?
Needs the 1098 matching box?
Anything else I might need to change if the newer engine?

Thanks everyone.

[shoebone]

sounds like your head gasket has blown .. check compressions

[oliver90owner]

Shoebone is likely correct.

If it is the gasket, do check for flatness of head (and possibly the deck). Is it possible the head was changed only 3k miles ago? It will likely fail again if the reason for the failure is not rectified.

RAB

[bmcecosse]

If 3 and 4 doing nothing - it's the head gasket..... Interested to know how you 'retimed' the valves.... Don't run the engine again till you lift the head.

[firehor5e]

Re torque after the first heat cycle too.

[vibrodolly]

Yes that makes sense.
I had a similar noise on a A40 once.
Would the noise not really be apparent on idle?

I can whip the head off no problem. done that before

[bmcecosse]

Of course! You are only running on two cylinders....

[vibrodolly]

Yup - blown between 3 and 4. Replaced head gasket.
No apparent damage or cause.
Some head bolts were not so tight at that end.

Thanks for the direction and help

[oliver90owner]

No apparent damage or cause.

Did you check for flatness of the head? If it is banana shaped, you will likely have another failure. I advise anyone who has a faied head gasket to check it out. More expense, but it will likey require that same cost, or more, when it next fails.

Only a couple of weeks ago there was a thread where someone simply replaced a blown head gasket, only for the poor owner to be faced with a £200 bill when it failed shortly afterwards. It is always sensible to find the cause and rectify the fault found before replacing with a new gasket. It only requires a few minutes with a straight edge and a feeler guage (or even a bright torch) to verify flatness of the head.

There is also a more recent thread where louisem had suffered a blown head gasket and the head required skimming to avoid a repitition of the failure.

RAB

[vibrodolly]

Ta thanks. The head has been skimmed 7000 miles ago. It was fully reconditioned.
It was more likely I hadn't torqued it properly as some bolts were not at all tight.

Thanks

Nick

[bmcecosse]

Always re-torque to 44 ft lbf after the first heat cycle -then reset valve gaps of course, with 15 thou on the ex valves.

[vibrodolly]

Oh dear - I got that wrong. Water out of the back of the engine between head and block.

[bmcecosse]

Off with it's head! Sure it's not just a leak at the heater valve ??

[vibrodolly]

Well I did think that, so will check properly when I get back after a few days. But, I'm fairly sure I can see water coming out between the block and the head. It stays in until I take the radiator cap off.

[oliver90owner]

Does this mean you have to replace the head gasket twice within a week? One good thing is that your rad cap washer is sealing well. You have under pressure in the cooling system while the cap is on. Likely the coolant would flood out if it gets hot and becomes pressurised.

Do you have a torque wrench? If so, has it been calibrated ever? Are you tightening the head in the correct sequence? Better check that head for flatness, this time! Replacing the head requires more care than 'whipping it off'! Presumably you have the correct studs and nuts (seen that once before, on an engine).

Reading back through this thread, I seem to note head at 7000miles , head 3000 miles, head three weeks ago and now head again? If this is a good time line, I think you need to check for flatness. The block deck as well, I would suggest.

RAB

[vibrodolly]

Yes - I'll check everything now.

If I've done more damage than is reasonably repairable, I have a spare 1098 (good) engine. Is it a straight swap?

[philthehill]

The top of the block must be checked for trueness especially the lands between the cylinders.
It is no good just checking the head - it takes two to tango as the saying goes - so both head and block must be true otherwise the head gasket will fail.
Phil

[bmcecosse]

My money is still on the heater valve - especially as it only 'leaks' when the rad cap is removed. But yes - if you have a 1098 it can be swapped over for either a 948 or 1098. Just retain the backplate and flywheel that's on your engine at the moment.

[vibrodolly]

And.... Heater valve wins!!

The base plate had lost it's thread.

I did think I knew what I was doing on a head, and it is torqued down correctly.

Thanks
Nick

[bmcecosse]

Easy fix then !