Place your bets!...

[DaveF-SkinnysAutos]

So, I've just taken into the workshop today a beautiful 1986 Mk1 Toyota MR2 (AW11).

Absolutely zero compression on any cylinder, but I can see on cranking that the timing belt is turning?!

However, when placed into gear and rocked forwards and backwards to try to move it to TDC the pistons aren't moving?!

The only background is the owner started it up in his garage, drove it out 5m and there was a bang!!

Stripdown starts tomorrow, how catastrophic do you think it will be?!?!

Place your bets, no prizes though!!

[E-bmw]

OK, a couple of questions.

Did you try hand-cranking the engine from the crank pulley? (pardon my ignorance if it isn't possible on that car)

Did he then manage to reverse it back into the garage?

When the bang happened did it stop running?

[paul_c123]

DaveF-SkinnysAutos said:

So, I've just taken into the workshop today a beautiful 1986 Mk1 Toyota MR2 (AW11).

Absolutely zero compression on any cylinder, but I can see on cranking that the timing belt is turning?!

However, when placed into gear and rocked forwards and backwards to try to move it to TDC the pistons aren't moving?!

The only background is the owner started it up in his garage, drove it out 5m and there was a bang!!

Stripdown starts tomorrow, how catastrophic do you think it will be?!?!

Place your bets, no prizes though!!

How have you determined the following:

1) Zero compression
2) Timing belt turning during cranking
3) Pistons not moving when turning engine (are you even turning the engine?)

[stevieturbo]

DaveF-SkinnysAutos said:

So, I've just taken into the workshop today a beautiful 1986 Mk1 Toyota MR2 (AW11).

Absolutely zero compression on any cylinder, but I can see on cranking that the timing belt is turning?!

However, when placed into gear and rocked forwards and backwards to try to move it to TDC the pistons aren't moving?!

The only background is the owner started it up in his garage, drove it out 5m and there was a bang!!

Stripdown starts tomorrow, how catastrophic do you think it will be?!?!

Place your bets, no prizes though!!

Usually the timing belt and pistons are not visible without some teardown.

So have you actually stripped part of the engine ? You say none of the pistons are moving ? Well clearly it would have no compression then.

A lot of info is missing here. Nor do you state whether the pistons are at a sensible height in the bore despite their claimed lack of movement.

[DaveF-SkinnysAutos]

More to come! I just wanted your early views on the info available from a very quick visit on site with no toolbox etc!

The facts from the customer were, he drove the car out of the garage, no more than 5m, he then couldn t get it into gear and there was a loud bang and had to get help to then push it back into the garage.

I turned up on site to have a look. No obvious holes in the engine block! It went into and out of gear when trying the gear selector at the gear stick. When you crank you can hear there is no compression. You can pull back the timing belt cover and visually see the belt turning on crank and turning the crank pulley and camshaft sprockets.

Spark plugs removed and car rocked back and forth to try to move it to TDC but the pistons dont move when rocked in gear.

Pistons do move when you hand turn the crank by hand.

Compression test shows no compression on any cylinder!

I just wanted to see all your ideas and train of thought before I start stripping it down, it was only transported over to me late yesterday so I ll update you as I go along.

I’m going for two issues, one gear related and one top end to do with valves and lifters?!

I’m not after your help in particular, the engine is likely coming out, I just thought it was an interesting initial problem to get your thoughts! If I need to I do a compression test on site I usually rock the car to find TDC rather than try to get to the crank pulley, hence initially having a real head scratch moment when I realised the pistons werent moving!

Edited by DaveF-SkinnysAutos on Thursday 26th March 09:51

[trevalvole]

DaveF-SkinnysAutos said:

I m going for two issues, one gear related and one top end to do with valves and lifters?!

Edited by DaveF-SkinnysAutos on Thursday 26th March 09:51

I'll play. My wild guess, in two parts as you suggest, is:

1. Clutch or diff;

2. For there to be no compression on all cylinders, something must have failed that is common to all of them, so my guess is that a camshaft has broken between the sprocket and the first valves.

[E-bmw]

Timing has slipped/jumped a few teeth.

Valves & pistons have clashed causing loss of compression.

The inevitable sudden stop has either trashed the clutch or the G/B input shaft.

[Peanut Gallery]

I'm going to put my money 50:50 on a broken crank near the flywheel or a broken flywheel.

Note that my money is Zimbabwean dollars, so worth zero.

[Megaflow]

Peanut Gallery said:

I'm going to put my money 50:50 on a broken crank near the flywheel or a broken flywheel.

Note that my money is Zimbabwean dollars, so worth zero.

That is where my mind first went to, but an engine of this age will have timing belt at the opposite end to the flywheel, so if the timing belt is moving on cranking, then the crank must be in one piece.

[Peanut Gallery]

Megaflow said:

Peanut Gallery said:

I'm going to put my money 50:50 on a broken crank near the flywheel or a broken flywheel.

Note that my money is Zimbabwean dollars, so worth zero.

That is where my mind first went to, but an engine of this age will have timing belt at the opposite end to the flywheel, so if the timing belt is moving on cranking, then the crank must be in one piece.

Doh, serve me right for skim reading, I read the bit where he turned it by hand..

Oh well, at least its only 50 billion dollars.

[DaveF-SkinnysAutos]

E-bmw said:

Timing has slipped/jumped a few teeth.

Valves & pistons have clashed causing loss of compression.

The inevitable sudden stop has either trashed the clutch or the G/B input shaft.

All interesting thoughts to date! I’m not an expert on the AW11 engines, but initial research suggests they are non-interference?

Anyway, I better get back to stripping it rather than reading these posts!

[ARH]

It's not going to make any compression if the pistons don't move surely.

[Megaflow]

That's the bit that is confusing me, how can the crank be rotating, but none of the pistons...

[TwinKam]

Megaflow said:

That's the bit that is confusing me, how can the crank be rotating, but none of the pistons...

Because the crankshaft isn't rotating when he 'rocks the car in gear', only on the starter... the centre has ripped out of the clutch.

[finlo]

TwinKam said:

Megaflow said:

That's the bit that is confusing me, how can the crank be rotating, but none of the pistons...

Because the crankshaft isn't rotating when he 'rocks the car in gear', only on the starter... the centre has ripped out of the clutch.

But how would that affect the compression?

[DaveF-SkinnysAutos]

Lunchtime update!

Defo two separate issues.

Crankshaft turns the pistons when turned by hand, but zero compression because only half of the valves are lifting suggesting some bend valves in there! So much for the ‘non-interference’! Timing looks a tooth out so its definitely jumped.

Flywheel is turning with the crank and nothing obvious missing, so fingers crossed no bottom end damage and the issue is gears or clutch related for crank not turning while in gear.

Something gearbox side has locked the crank causing it to jump the timing and smash the valves?

[E-bmw]

DaveF-SkinnysAutos said:

Lunchtime update!

Something gearbox side has locked the crank causing it to jump the timing and smash the valves?

Sounds feasible & if it turns out to be true, I was pretty close, well see when you get it fully apart, either way I am definitely watching.

[TwinKam]

DaveF-SkinnysAutos said:

Lunchtime update!

Defo two separate issues.

Crankshaft turns the pistons when turned by hand, but zero compression because only half of the valves are lifting suggesting some bend valves in there! So much for the non-interference ! Timing looks a tooth out so its definitely jumped.

Flywheel is turning with the crank and nothing obvious missing, so fingers crossed no bottom end damage and the issue is gears or clutch related for crank not turning while in gear.

Something gearbox side has locked the crank causing it to jump the timing and smash the valves?

There's very little inertia in the valve train, certainly not enough for it to do that, else it would happen every time you stalled!
Two events, as you said, but somehow linked: clutch centre fails, drive is lost, engine over revs... is the exit from the garage uphill or over a ridge, requiring a burst of power?

[DaveF-SkinnysAutos]

TwinKam said:

There's very little inertia in the valve train, certainly not enough for it to do that, else it would happen every time you stalled!
Two events, as you said, but somehow linked: clutch centre fails, drive is lost, engine over revs... is the exit from the garage uphill or over a ridge, requiring a burst of power?

Nope, exit from garage is completely flat.

Bit more detail for you mechanical detectives! Customer knows nothing about cars (but it's a real Mint car that he's had since new, only 45,000 miles on it since 1987!) The background as conveyed to me is, in October 2025 the clutch pedal just dropped to the floor, he had out a mobile mechanic who changed the clutch. Since then it's only driven a mile at the most. He went to take it out last week, got it 5m out the garage, heard a pop and it wouldn't start. The next bit is a bit confused but the thinks he couldn't push it back into the garage as it wouldn't move like it was in gear. A friend helped him and they got it out of gear and pushed it back into the garage, but he isn't really clear on this part.

Anyway, hopefully got the head off tomorrow to look at the top end, but still some head scratching at the flywheel end for now!

[E-bmw]

In that case the only issue will be the clash of valves with pistons and a dragging calliper or similar.