325 cam belt failure Update: rebuild in progress :)

[spiny]

Hi again everyone,
not my week with my 325 :/

just had the cam belt go this evening and i'm after pointers on how to go about checking and/or fixing it.

I was pottering along in traffic at about 20mph when a real loud rattling started, like a loose exhaust or something, I was about to pull over, when it stopped suddenly. I though it might have been something stuck in the fan, so carried on, but 30 seconds later it started again, by this time I was stopped in traffic, reving the engine felt very underpowered and rattly, as if it wasn't firing on all 6, then when i let it idle, it was erratic for 10 seconds or so, then cut out totally.

trying to restart gave the 'real quick starter' noise, and on checking the engine bay, there were flakes of cam belt all over the place and a bit sticking out from the plastic cover.

as it stands, I've just had the car recovered home and I am drinking beer.

my ideas:

1: presumably the best thing would be fit a new belt, then compression test all six cylinders and if all is well, try and start it ?

2: if all is not well in '1' , then pop the head off ?

is there a good guide on replacing the belt online ? the last one I did was on a 2l Cortina

[cecotto479]

I'd take the head off first. No point in putting a belt on it and doing a compression test in my view. There'll be bent valves at the very least.

[bmw9818]

if the belts snapped it probably has damaged some valves and if its rattling contact has probably been made, doesnt hurt inspecting it just pull the head off and have a look,

id probably just get another engine and drop it in if its smashed the pistons and damaged the bores etc

[spiny]

cheers guys.

[bmwbmwbmw]

sorry to read about your cambelt, but it is a engine change time for you, bad times, very bad times

[Andy325i]

Time for a 24v conversion

[spiny]

I know zero about engine swaps, but is this as compatable as the advert says it is ?

http://www.ebay.co.uk/itm/bmw-520i-engi ... 1c2a5b9d5e

how 'bolt in' are swaps in general ? is it juts a case of collecting the right parts, or is there fabrication needed ?

[mcbonio]

I'd just source a good m20b25 from one of the guys from here.!

[spiny]

I'd just source a good m20b25 from one of the guys from here.!

yes, that would probably keep things simple


I'll pop the head off over the weekend and see whats kanckered.

[mcbonio]

I think damage varies greatly when he timing belt goes, valves bent even busted through pistons! There was a fella on here who belt went and it only snapped a rocker arm. Have a look, might not be that bad.

[spiny]

I think damage varies greatly when he timing belt goes, valves bent even busted through pistons! There was a fella on here who belt went and it only snapped a rocker arm. Have a look, might not be that bad.

i'm crossing my fingers here, as it was running when making the 'very loud noises' and I could rev the engine. of course it could have slipped a few teeth and the noise was a piston being eaten, but i'm a glass half full person

taking the head off won't cost me anything other than time, and I'll learn something, so it's not all bad

the 'change the head gasket' wiki article seems to cover everything, even if it looks a bit daunting

[mcbonio]

Nah like anything it can only come apart and go back together one way. M20 engines are super easy to work on.... My brothers supra jza80 engine has broken a valve.. Not looking forward to fixing that ..

[Andy325i]

I know zero about engine swaps, but is this as compatable as the advert says it is ?

http://www.ebay.co.uk/itm/bmw-520i-engi ... 1c2a5b9d5e

how 'bolt in' are swaps in general ? is it juts a case of collecting the right parts, or is there fabrication needed ?

The easiest thing would be to pull the head off of yours, worst case you get another secondhand M20B25.

Engine swaps are well worth it, but aren't cheap, think £1k upwards.

Lol at the advert, don't think anyone would bother going to all that effort to fit a 2 litre 24 valve into an E30! Or anything else for that matter. Nice to see the seller lists it as fitting an E34 M5, nice eco mod for them

[spiny]

Nah like anything it can only come apart and go back together one way. M20 engines are super easy to work on.... My brothers supra jza80 engine has broken a valve.. Not looking forward to fixing that ..

it's the billions of hoses and wires that worry me

I've owned various VW buses since I passed my test about 20 years ago and they are nice and easy to work on my other project at the moment is a '70 MG Midget, another low hose/electric count engine, and when I had my cortina, swapping a head was about 1/2 an hours work (after a few goes practice)

[spiny]

ok, spent an hour dodging the rain taking the various hoses and things off to get to the cam belt and it's not -actually- snapped ?
there is a lot of defelection in it though, i can almost turn it 180degrees.

sooooo, could the loud noise i heard have been the missing bits flapping about, hence why it stopped suddenly (the noise that it) ?
also, and i'm crossing fingers here, could the stall and non-restart be because its stretched and slipped a few teeth ?

turning it over with a 22mm spanner on the bottom pulley seems to wortk and theres no obvious tight spots or nasty noises, and turning it over on the starter seems to go ok too, all the rockers move, though i guess if the bottom of a valve had punched through a piston it's not really possible to tell from the top of the head.

first Q:

how do i tell if the belt has slipped, presumably I follow the guide for fitting a new one and check the marks ?

some pics:







cheers, Phil.

[johnl320]

Check timing, renew belt, compression test

[spiny]

i checked the marks ane theybare out, so will try a new belt typing 9n my puone on a bus rght now, apologies for typos, bumpy road

[mcbonio]

Wow you got lucky.. why has the flat side of the belt worn out like that?

[daimlerman]

Wow you got lucky.. why has the flat side of the belt worn out like that?

Cambelts should be changed at three years or 30k miles,end of.

Belt costs £10ish,rebuilt M20?
Not much change out of £1.5k....

[B7]

Looks to me like the tensioner may have failed or come loose.

I would strip the front of the engine right down (which you need to in order to change the belt), check theres nothing jammed which has been chafing the belt and fit a new tensioner and belt. then turn it over again with the plugs removed and ensure it turns over ok and all the rockers are moving.

Then put it all back together and start it. I reckon you caught that just in time!!!

[spiny]

I'm off to my local GSF to get a belt kit in a minute

as far as I can tell from the paperwork I have, the belt has only been on for about 18k miles, but.... it was done about five years ago, my bad !

I'm hoping that part of the broken belt got inbetween the belt and one of the pulleys, making the belt slip.

well, the weather here is nice, so I should have the time to strip the rest down and check everything.

I'd also like to thank whoever fitted the last viscous fan, as they seem to have copperslipped it as it came off really easily

[spiny]

Ok, whats the trick for removing the second tensioner pulley bolt ?



it appears to be stuck solid, i've tried a 12mm on the bolt itself and the 'two nut' trick to try and wind it off, but it doesn't want to move, I don't want to force it, as if it snaps off, it'll be game over.

should the tensioner move 'freely' with the top bolt out ?

I have a new tensioner to go on, just in case.

thanks:)

[spiny]

doh, the 17mm 'washer bit' is the trick

[daimlerman]

If it's not too late.....

When you re-assemble,turn the engine two complete turns using a 22mm spanner on the crankshaft nose bolt,then re-check that the timing marks line up.

[spiny]

ok, something is amiss ...


I did the 'turn twice' check and everything stays lined up after two rotations, but when I tried to start the car, it seemed to spin quite quickly (though this could be my imagination) but wouldn't fire. I tried a few times after rechecking al the wires and on the third try it still wouldn't start, but did make a massive backfire.

soooo, I took it all apart again and everything was still lined up, so I did a compression check which showed zero on the four plugs nearest the front of the car (my plug socket is too big to do the back two) I did check the gauge on my MG to make sure it wasn't broken, and it isn't :/

sooo, then I took everything apart again and span it on the starter with all the covers off, and everything -looks- like it's setup correctly, trying to start in gear makes the car move too.

the no compression is obviously the worrying bit here, presumably there isn't anything that can cause this that isn't smashed valves / pistons ? :/

one last question, it is possible to time it 180 degrees out ? I did wonder but I guess that on an interference engine it's not possible to rotate the bottom pully one complete revolution without the pistons hitting valves ?

yours, very sad.

[Brian28]

Most likely bent balves on front cylinders, 180 out wouldn't make any difference to not having compression. With any luck, you will get away with head off and a handful of valves. Spinning over quicker isn't your imagination - no compression

[spiny]

arses.

oh well, time to take the head off then.

[FinalD]

Yeah, sounds like you've had some piston on valve action, just hope it isn't as 'good' as mine.

It is entirely possible to line it up 180deg out, I pretty much did that when fiddling about with the dead engine. The timing marks on mine are a complete pain to see properly, luckily my replacement engine is all timed up correctly on a new belt and tensioner.

My old one had a failed tensioner which resulted in the belt running slack and skipping which caused the above (and snapped a rocker).

[spiny]

I'll be making a start this evening, got the torx tool on order to get the head off, so I'll be stripping everything off ready.

I feel like I could change a cam bely my feel along now, the amount of times I've had the front of the engine in pieces ..

[spiny]

ok, three of the lower manifold nuts are totally rounded off - a 12mm socket just spins and an 11mm one doesn't quite fit.
is it game over ? theres no way to get it onto ramps as it's parked on a gravel drive.

[Grrrmachine]

7/16ths socket, hammered on. Or slitting discs on a Dremel.

If you can, get a 12mm socket with 6 sides, not 12. They have a better bite to them. You might only find them in 1/4", so you'll need an adapter to a beefier wrench.

[Brian28]

If you're stuck take the head off with the manifolds attached, it's a lot easier if you can get a mate to give you a lift with it.

[spiny]

I nearly gave up there ..

my 7/16 was too tight, but I did find some cheapy long reach sockets that were six sided, and with some gentle encouragment smashing an 11mm on then tapping a 12mm on after, I've managed to get them all off.

all bar three have wound the studs out too, but none have broken, which is a relief.

time to read more on the wiki and see how much of the inlet side needs to come off.

presumably, i'm gonna have to crane the head off ? as I'm guessing it's not light ?

[clipper]

presumably, i'm gonna have to crane the head off ? as I'm guessing it's not light ?

It's not that heavy !

I'm about 5' 7" and 8 and half stone and do no sport and I lifted my M20 head off on my own.

(Called a 6 ft tall mate with black belt in Karate to place it back on for me though )

[bmw9818]

its quite heavy, i had my car on stands cause i was doing the struts so it was a bit difficult to lift it up and off, but i did it use the inlet and exhaust ports to grip it and pull it off