Compression testing

[Ahmedsinc 414]

Have you removed the ac pulley from the crank? As silver fox said those bolts might need replacing with shorter bolts

Negative dude, crank pulley is 100% unmolested

[Ahmedsinc 414]

Compression test should be done with plugs removed, throttle wide open and then cranked via the diagnostic socket so that no power goes to any other circuit, just the starter motor. The vanos should be left undisturbed/no power to it.

Seeing it is on a stand with manifolds and cams removed (so valves should all be closed), a quick way to check if you have bent valves will be to put some paraffin/diesel into each cylinder, replace the spark plugs and then invert the engine. if the valve/s are bent, the liquid will escape rapidly. Dont forget to drain the oil first. Alternatively you can use a leak tester. If this shows bent valves, then off with its head...

However, from your description, I suspect something has gone wrong with the chain/tensioner causing it to lock the crank from turning in either direction. (top end failure will normally not lock the motor solid in either direction unless it is a catastrophic failure, your work on it should not have this result). I would firstly remove the sump and have a look from the bottom. See if the chain is hooked up somehow. (It should be loose as the cams are out).

Let me know what you find.

Well I guess that answers the question. Grabbed a litre of kero on the way home, dribbled done into each pot and inverted engine with plugs in and sure enough, leaking out of exhaust ports, 3,4 & 6 definitely worse than the others

So I suppose the next question is am I better to use the heavier valves from the spare M50B25Nv head or the ones from the M52B28TU?

Bugger bugger bugger bugger bugger bugger bugger bugger!!!!!!!!

[Ahmedsinc 414]

Just whipped the sump off with engine inverted, can't see anything that could foul the chain. Whatever's caused the engine to lock must be in the head or bore/s.

Don't understand why it refuses to move counterclockwise though

[Ahmedsinc 414]

Just thinking some more........ if valves are bent is it plausible for them just to be on the exhaust side? I'd have thought bending all 12 on the same side would be pretty rare if not impossible.

Have seen a thread on bimmerfest where a poster suggested disintegrated timing chain rails were the culprit. Removing timing chain cover tomorrow to have a better look.

Watch this space

[polley 916]

A friend over revved his m52 (9000+rpm) and it bent all the exhaust valves.. Intake were fine.

[elmarco 56]

Guess it depends on the cam lift - it is feasible (and I have no idea what grind they have) that exhausts have higher lift than the intakes. Where did the motor come from & have you seen it running?....

[polley 916]

I believe that generally the intake would have more lift. No idea why the exhaust valves floated before the intake, but I noticed the same happened on my bike when it over revved, exhaust valves floated before intake - and it was only the ones on the rear cylinders (V4) which are known to run hotter then the front. So maybe its related to temperature / valve springs becoming softer with heat.

[Ahmedsinc 414]

Solved the seized crank issue. Flex plate bolts were reinserted on tte crank after comp testing. Took engine off stand, removed bolts and she moves free and easy.

It should also be noted that this was done after the head came off.

f**k!!!!!!!!

On the upside, everything is kosher within the block. On the downside, I need a new HG and bolts. Oh, and I'm an idiot.

[elmarco 56]

Give yourself an uppercut.....

At least you know now!

[Ahmedsinc 414]

I've been debating for months whether to replace the head gasket or not for peace of mind - I have my answer now

Back to an earlier question - will M50B25NV valves fit ok? I understand NV valves have stiffer springs and thicker stems - will this be of any advantage to an otherwise standard NA engine? Since I have to sort out the exhaust side I might as well do the inlet if there's any benefit

[polley 916]

The nv valves are heavier and stems take up more room in your ports

[Allanw 1051]

Suggestion: M54's have been known to strip headbolt threads in the block... Usually after over heating though.

If it were me, I'd timesert all the headbolt holes (I'd ONLY use Timeserts too - NOT helicoils (which can expand on the way out, and destroy the block, if you ever have to get the head off again)).

You can buy the kit (but it's about $500, though you can put about $40 worth of inserts back in, and sell the kit afterwards), or find a machine shop that has one - Someone in Auckland will have one, Shirley

[B.M.W Ltd 950]

I'd use Taylor Automotive to do the inserts

[Ahmedsinc 414]

I'd use Taylor Automotive to do the inserts

Any estimate on cost Glenn?

[B.M.W Ltd 950]

Any estimate on cost Glenn?

You'd best ring Tom 3778404

[thorburn 120]

I believe that generally the intake would have more lift. No idea why the exhaust valves floated before the intake, but I noticed the same happened on my bike when it over revved, exhaust valves floated before intake

Guess it depends on the cam lift - it is feasible (and I have no idea what grind they have) that exhausts have higher lift than the intakes. Where did the motor come from & have you seen it running?....

Intakes have more lift and longer duration.

The reason the exhaust valves are more likely to bend is because how the engine cycles.

When the intake is closing the cylinder is on the way down.

When the exhaust is closing the cylinder is on the way up.

Glad there isn't foreign matter in the engine.

[Ahmedsinc 414]

Intakes have more lift and longer duration.

The reason the exhaust valves are more likely to bend is because how the engine cycles.

When the intake is closing the cylinder is on the way down.

When the exhaust is closing the cylinder is on the way up.

Glad there isn't foreign matter in the engine.

True, 9.7mm vs 9.0. Explains that one nicely! Plus it means I only need to replace 12 valves, not 24.

Me too man, aside from 1mm +/- carbon deposits everything looks to be in good order. Placing the order for HG and bolts through Pelican tomorrow, anything else I should stick in the box?