Failed 172 Engine? But Why? some questions answered please

[MrStabby]

Well 2 weeks ago, the day after I changed my throttle cable on my Ph1, going to work, had done about 10 miles or so and lost all power. Coasted to the hard shoulder, turned off and tried to start, car was cranking,but not firing (not very good with engine lingo). Very odd noise it makes. Electrics seemed Ok (car cranks on ignition)

Had to get recovery to drop me to work. Next day started stripping off the inet etc, no metal shards found, oil seems Ok (no mayo etc). Checked AUX belt, ll in tact. Could hand crank the engine, and can see Cams moving so wouldn't say Cambelt has snapped. Tried a compression test but getting no reading whatsoever on any of the cyclinders?? Haven't bothered to take top mount off to inspect Cambelt and didn't see much point. The noise ins't healthy, but never heard a massive bang. Any ideas?? Spoke to a couple of tech's and they reckon Cambelt may have jumped a tooth or to. Reluctant to pay out to have the head removed, as would prefer to get a 2nd hand engine, have cabmelt, aux, waterpump and clutch done.

Was thinking about stripping lower inlets to see the state of the valves but seems like hastle Also the calm seemed alive (more free flowing, power delivery) the day after I changed the throttle cable, pressume this was just due to the old one being frayed and catching.

 

[Russ_16v]

If you have no compression then cylinders are not sealing, so my guess would be along the lines of the cambelt has jumped and bent valves, sorry to hear mate

Did it spin over quicker than mormal? less compression can make cranking speed faster due to less resistance (ie valves not seating properly)

 

[Dan519]

pulleys slipped and bent the valves imo. common

 

[Russ_16v]

How often do you see it out of interest Danny?

tis a shame, probably worth going for a 2nd hand engine if you can find a known working one, unless you can carry out the repair work yourself

 

[MrStabby]

Thanks for the advice lads, going to source a 2nd hand engine, since its a ph1 172 can I go for any lump?

 

[Danith]

pulleys slipped and bent the valves imo. common

Common due to incorrect cambelt fitment? Or common in general?!

 

[Dan519]

Common due to incorrect cambelt fitment? Or common in general?!

bit of both, usually incorrectly torqued bottom pulley bolt, or something gets tangled round the pulley (damaged aux belt etc)

Russ, don't see it much recently as fewer people pay for repairs. Cars usually sold for spares or fixed at home. Sure it'll hit mk3s soon enough

 

[Russ_16v]

Thanks for the advice lads, going to source a 2nd hand engine, since its a ph1 172 can I go for any lump?

yes mate

bit of both, usually incorrectly torqued bottom pulley bolt, or something gets tangled round the pulley (damaged aux belt etc)

Russ, don't see it much recently as fewer people pay for repairs. Cars usually sold for spares or fixed at home. Sure it'll hit mk3s soon enough

Cheers Danny

 

[Dan519]

id rebuild that. its only some valves, and youll end up with a rebuilt top end rather than an unknown whole engine

 

[Chip-mk1]

Suddenly having zero compression on all cylinders is always bent valves, head gasket going or rings going etc isnt as sudden or as conclusive (ie you normally get low compression not none)

The good news is that because the valves are relatively slim stems and are at a fairly steep incline it takes very little force to bend them badly, which means that the pistons normally survive.

Secondhand head or a secondhand set of valves are both cheap options, only made expensive by the fact that belt and gasket are fairly dear compared to a lot of other engines.

 

[MrStabby]

hmm decsions. What kind of costing would I be looking to replace the valves? Pressume this all reliant on the head being stripped and inspecting the damage, hoping only as you say valves are bent.

 

[ya53lhd_MATT]

I Just bought a full head gasket and valve kit (seals etc) for £140 odd quid, mk2 172 cup engine.

 

[mgoode180566]

that is precisely what happened to my phase 1. just stopped with all belts in place. checked compression and all cylinders had gone. i replaced it with another engine from a phase 1 . really pleased with it and by doing it myself worked out good financially. i did find my problem but i think it was quite unique. the bottom pulley fell in half and jammed the cambelt which caused it to jump a tooth. when i cut the aux belt off the bottom pulley just disintegrated into 2 parts.

 

[Chip-mk1]

I Just bought a full head gasket and valve kit (seals etc) for £140 odd quid, mk2 172 cup engine.

That doesnt include new valves themselves though of course (just in case anyone reading it thought it did)

 

[Laine_16v]

Dont use pattern part valves, i had a bad experience. I would take the plunge and buy new OE renault valves, or a set of 2nd hand renault valves and spruce them up.

 

[Laine_16v]

That doesnt include new valves themselves though of course (just in case anyone reading it thought it did)

It probably does, trechii is pretty cheap for all that sort of stuff, about £30 per set of 8 valves. (but they are crap)

 

[Chip-mk1]

It probably does, trechii is pretty cheap for all that sort of stuff, about £30 per set of 8 valves. (but they are crap)

Oh, good point, I completely forgot that people are still silly enough to put non genuine parts on these cars.

I would take a 100,000 mile old secondhand standard set over a cheap and nasty new sub-standard set every time!

NEVER put cheap valves in an engine doing 7Krpm+!

 

[mark123]

Ktec have genuine cambelt kit for 130 and genuine headset for 100. When I was looking around a couple of weeks ago pattern parts were no cheaper.

Head bolts are 76 on ktec for genuine but I did find them for around 30 quid from ecp etc.

hmm decsions. What kind of costing would I be looking to replace the valves? Pressume this all reliant on the head being stripped and inspecting the damage, hoping only as you say valves are bent.

 

[mark123]

Oh, good point, I completely forgot that people are still silly enough to put non genuine parts on these cars.

I would take a 100,000 mile old secondhand standard set over a cheap and nasty new sub-standard set every time!

NEVER put cheap valves in an engine doing 7Krpm+!

Unless you're in the know though. It is very difficult to know when pattern parts are ok or not.

 

[Chip-mk1]

Unless you're in the know though. It is very difficult to know when pattern parts are ok or not.

Agreed, in the case of the 172 engines though, people should just go with everything genuine or uprated, never cheap pattern parts.

 

[ya53lhd_MATT]

Just caught back up with this thread, ohhhh pants!!! enough said.

 

[ya53lhd_MATT]

Surley they must conform to some sort of standards? I've just bought a set of CAMTEC Valves, am i doomed?

 

[Laine_16v]

Mine were CAMTEC valves, like i say it didnt end well...

Should be noted the headgasket i used and headbolts were both CAMTEC too, and have used them on a couple of engines with no issues at all.

 

[ya53lhd_MATT]

Were the engines you had no issues with F4R's aswell? I've got a CAMTEC head gasket and head bolts too, all the valves are ground in now aswell :/

 

[Laine_16v]

I mean its not as if i was giving the valves an easy time, i was using 421 cams which will increase the stress on the valvetrain by a bit, and they did explode at 7500rpm.

But IMO F4R's should be able to rev to 7600rpm without issue, so i blame the pattern part valves.

 

[Dan519]

valve guide wear/damage, causing the valves to seat unevenly when they close can put a lot of extra stress on the valves.

That's a pretty good read:
http://bgautomotive.co.uk/Media/dow....8L - 2.0L 16v F4P-F4R - A5 FORMAT - 2010.pdf

I don't agree with every word of it, but it's a valid arguement