Author Topic: Cam chain jump guard  (Read 14670 times)

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Offline TomL

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Cam chain jump guard
« on: February 27, 2015, 12:15:59 am »
This is a copy of the information I posted on the old EuroKClub forum about the problem I encountered when my cam chain jumped after I had filled up with petrol after a weekend in Wales.

BMW K series slant four engine cam chain jump guard.
Those of you with BMWs with the K40-K43 engines (K series slant four engines) should by now be aware of the problems caused by the camchain climbing around the crankshaft sprocket as shown in this photo of my engine.

This problem can be prevented by fitting a camchain jump guard part number 111318526932 which costs about £7.

If you're not sure if this is fitted to your engine you can check by removing the large aluminium plug shown in this photo in the right hand clutch casing cover. This requires a T60 torx adaptor.



The cam chain jump guard is not fitted if the crankshaft sprocket teeth are visible to the right of the large hexagon on the end of the crankshaft.

When my cam chain jumped on start up the noise was horrendous. Luckily I guessed what had happened and decided not to restart it.

It cost me about £135 to change the cam chain, cam chain guides, camshaft sprocket and fit a cam chain jump guard. BMW recommend replacing the aluminium clutch cover bolts but I re-used the old ones.

The consequences of the cam chain jumping could completely wreck the engine with valves hitting pistons.
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Offline bobtail

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Re: Cam chain jump guard
« Reply #1 on: February 27, 2015, 09:25:56 am »
Paul, wasn't that rectified as a standard recall?

Bob
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Offline Costas

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Re: Cam chain jump guard
« Reply #2 on: February 27, 2015, 10:06:52 am »
Is was a recall but not a standard one, was left to local dealers world wide to have their back in the shop for the guard installation. So it appears that even today we have issues, it is still a very valuable info and anyone riding  a K bike should check with his dealer if the bike has undergone that recall.
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Offline bobtail

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Re: Cam chain jump guard
« Reply #3 on: February 27, 2015, 10:28:09 am »
Costas I do remember my dealer doing it when it went in for it's annual service maybe I've just got a very conscientious dealer.

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Offline Phmode

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Re: Cam chain jump guard
« Reply #4 on: February 27, 2015, 11:23:06 am »
To protect your engine from destruction you need the jump-guard together with the new-style, larger cam-chain tensioner, identifiable by being approx. 2.5" or 63mm tall.

The new cam-chain tensioner is the FIRST LINE of defence against the dreaded cam-chain jumping the teeth on the crankshaft sprocket.

The cam-chain is held in tension by a hydraulic system which is fed from the engine oil pump system. As the engine oil pressure builds up, this forces a piston down, which in turn pushes a sled against the chain to keep it tight and stop chain slap, noise and tooth-jumping. This problem is caused by the old-style tensioner leaking oil back into the sump after standing for a while with the engine off, particularly on the side stand.

If this happens, the cam-chain is slack on engine re-start and this slackness causes a VERY, or just a SOMEWHAT noticeable rattle for a few seconds when the engine is started. In extreme cases this slack can allow the chain to jump the teeth with potentially disasterous results.

If the chain does jump the teeth, this loses the synchronisation between cranckshaft (and therefore the pistons) and the cam-shafts (and therefore the valves) which can result in the valves and pistons colliding. Ouch! And very £€$¥ as this can result in bent valves and broken pistons which means a full engine strip and lots of new, expensive parts.

The new-style tensioner has an oil reservoir built in which in theory holds enough oil to ensure that the tensioner is fully up to pressure when the engine re-restarts.

The rattle on engine start is not, in and of itself, disastrous; it is merely a symptom of the problem existing and can mean one of two things, either you still have the old-style tensioner OR you have the new-style tensioner (which was fitted in production in 2011(?) ) AND it is getting worn. There is a small 'O'ring seal which costs pennies and takes minutes to fit and which will restore the ability of the tensioner to hold oil and in theory stops the chain becoming slack and noisy.

This is where the 'jump-guard' comes in. Despite having the new-style tensioner (and for all bikes with the old-style), the chain can still get slack if the 'O' ring seal goes and therefore the chain can still jump the teeth etc. etc.

The plastic 'jump-guard' that Tom so clearly describes, was fitted as a 'back-stop' and is the second line of defence in the sequence. If the chain gets slack and the chain attempts to 'climb up the teeth', the chain will make contact with the plastic sheild and NOT be able to jump the teeth!

So kiddies, we ALL need BOTH the new-style tensioner AND the jump-guard fitted to our K12 or early K13 bikes, noisy or not. There is nothing else between you and disaster; regular servicing and maintenance makes no difference. Make sure you have em or get em fitted now!

Brian (who never thinks sticking plasters are a satisfactory solution to a problem caused by bad design

Offline TomL

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Re: Cam chain jump guard
« Reply #5 on: February 27, 2015, 11:52:16 am »
My bike does have the latest tensioner fitted but it still jumped.

My bike started to rattle at start up and while I was at the dealers having another recall done, I asked the mechanic about the rattle on start up. You guessed it, he said "they all do that, nothing to worry about". Not being happy about it, I googled and found out what was causing the rattle and went back. They agreed to fit the new style tensioner with oil reservoir. They rectified the rattle by taking some shims out of the old tensioner with the excuse that they couldn't get hold of a new tensioner. I insisted and they fitted the later tensioner the following week.

I read about the cam chain jump guard on the internet and asked about it at the dealers. They hadn't heard of it. I went back to the dealers with the part number of the guard and they said that it had been discontinued. A few months after that my cam chain jumped. So much for the dealers. I'm so glad that I don't have to take my bike into a main agent for servicing or repairs.

It should be noted that on the first K1200S engines the crankshaft sprocket was bolted to the end of the crankshaft and was replaceable. On my engine it is part of the crankshaft meaning that when it is worn out the only way to replace it is to fit a new crankshaft. Good design??

For some reason the cam chain jump guard was never a recall and was replaced surreptitiously when bikes went in for servicing. What is that all about??
« Last Edit: February 27, 2015, 11:54:37 am by TomL »
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Offline Phmode

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Re: Cam chain jump guard
« Reply #6 on: February 27, 2015, 01:11:08 pm »
....and my dealer at the time recommended I have the tensioner fitted (at my cost) whilst it was in for service. They also fitted the guard FOC as a tickler for past sins on their part. Subsequently BMW authorised the dealer to re-imburse me for the cost of the tensioner.

Brian (who thinks the whole sorry tale was and still is, a debacle of mind-numbing enormity)

PS My comments were for the benefit of the wider community Tom. I had read your tale on the old site.

PPS As the chain must rub against the guard at some point in its life, one wonders if it is a serviceable item in future years or are BMW not expecting any of our bikes to be around that long.

PPPS What year did the one-piece crank assemblies arrive? Mine is an Oct 2004 so should be OK!

Offline chriscanning

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Re: Cam chain jump guard
« Reply #7 on: February 28, 2015, 09:33:21 am »
When you guys have a minute google BMW 330D cam chain problem I only stumbled across this while looking for one it's seems to be in BM's DNA  ::)

Offline Phmode

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Re: Cam chain jump guard
« Reply #8 on: February 28, 2015, 09:40:48 am »
Er, yes! While looking for the supplier of the manual adjuster I was amazed at how many BM threads there were for cars with the same problem!

Brian (who can imagine the conversation in the BMW boardroom when they wanted to change their biking demographic; 'we'll get the car boys to do it, they know a thing or two about sporty motors'

Offline TomL

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Re: Cam chain jump guard
« Reply #9 on: February 28, 2015, 02:03:12 pm »

PPPS What year did the one-piece crank assemblies arrive? Mine is an Oct 2004 so should be OK!

It is not clear from any of the parts lists available to us when the one piece crank started. I've only just realised that the Rainbow parts list does not delve into details such as the actual year of the bike.
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Offline gramey

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Re: Cam chain jump guard
« Reply #10 on: March 20, 2015, 09:12:40 pm »
Having bought my bike last Saturday I phoned BMW as although the service book is stamped there were no past invoices with the bike which had been serviced at the Emergency Services workshop in London. BMW told me it had not been for four recalls which as they described them to me were , cam chain guides ( not sure if he meant the tensioner or the jump guard referred to here), something to do with the fuel pump, a rear suspension relay link?, and a something to do with the brake reservoir. Having read about the rear wheel flange recall I asked them and they said BMW would write to me about the rear wheel flange if it affected my bike.

Sorry I've gone off topic a bit but how do I check if I have the later cam chain tensioner, it's going into the dealers next Tuesday?  :)

Offline chriscanning

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Re: Cam chain jump guard
« Reply #11 on: March 20, 2015, 10:14:37 pm »
Blimey where do we start ;) having seen your posts on the American site the paint you need you can get from here.

http://www.rsbikepaint.com/en-gb/colours.php

It will probably be the tensioner and the jump guard and until you have both I wouldn't be overly keen on using the bike.

The new Tensioner will look like this



You can take the cover off the side to check for the jump guard but little point as the chances are you haven't got it.

The rear suspension is this it isn't actually but that's what they change because water can get in behind the photo is the Sandbar version.



But to cure 'Tank' feel of a stock K make sure you have 55 rear tyres and a set of these or similar

http://www.sandbarcomposites.co.uk/displayproduct.php?product_id=645&category_id=120

The fuel pump is no big deal and as for maybe having a dodgy flange Ooh Errr you can check that yourself but BM UK get through stuff like that fairly quickly
« Last Edit: March 20, 2015, 10:47:39 pm by chriscanning »

Offline TomL

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Re: Cam chain jump guard
« Reply #12 on: March 20, 2015, 10:30:02 pm »
Having bought my bike last Saturday I phoned BMW as although the service book is stamped there were no past invoices with the bike which had been serviced at the Emergency Services workshop in London. BMW told me it had not been for four recalls which as they described them to me were , cam chain guides ( not sure if he meant the tensioner or the jump guard referred to here), something to do with the fuel pump, a rear suspension relay link?, and a something to do with the brake reservoir. Having read about the rear wheel flange recall I asked them and they said BMW would write to me about the rear wheel flange if it affected my bike.

Sorry I've gone off topic a bit but how do I check if I have the later cam chain tensioner, it's going into the dealers next Tuesday?  :)
Take a look at the photos at the start of this post and I explain how to check if you have a cam chain jump guard fitted. The tensioner will require attention if there is a clatter on start up that goes away after a few seconds. 
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Offline Phmode

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Re: Cam chain jump guard
« Reply #13 on: March 20, 2015, 10:40:47 pm »
....and the rear suspension linkage (the dogbone link) is a potential killer! The rear suspension can seize and the resultant rock solid rear end can give way at the most inopportune moment; I believe the first appearance of this was a guy sliding down the M4 a few years ago after his rear seized in lane 3 in heavy rush-hour traffic.

BMW paid for a new bike, replaced all  his clothing and suitable compensation.

Brian (who is shocked at the emergency services cavalier attitude to their rider's safety)

Offline chriscanning

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Re: Cam chain jump guard
« Reply #14 on: March 20, 2015, 10:45:38 pm »

[/quote]
Take a look at the photos at the start of this post and I explain how to check if you have a cam chain jump guard fitted. The tensioner will require attention if there is a clatter on start up that goes away after a few seconds. 
[/quote]

Even with the new tensioner and 5/40 mine will still rattle when it feels like it and I know Timbox's used to as well and he'd got a trick seal on his to help the job along.