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MG MGF Technical - Cam shaft pin failure
Just a quick post to see if anyone else had a similar problem to me. A month or so ago my MG F died (1.8 VVC UK spec full rover SH 20K R plate). A HGF has suspected so it went (under warranty) to a rover dealer for a fix.
After several weeks of hassle I moved it to a mg specialist who took the head apart and diabnosed the problem as a cab belt failure. On further investigation it appears that the first failure was the little pin that joins the cam shaft to the sprocket.
Has anyone else had the pin break or have any ideas as to why it broke on a relativly new engine.
Thanks in advance
|A german chap, regular to this BBS sometimes reported such a failure 2 weeks ago from his VVC.|
From my memory he talked about a kind of 'rolled pin' which already got bended from torque between cam shaft and sprocket? (spelling?).
I'll send him a hint, so he can explain himself here .
|Hmmm quite interesting.|
If the roll pin is being compressed then this is simply bad assembly. However over the last couple of weeks I have had the MGOC MGF in pieces for what was clearly it's second HG failure. (Dieter, it is an early 1997 car)
There was more than a gasket failure when stripped!! A mark in the head face directly under the gasket fire ring for number 3 cyl. This was allowing combustion pressure into the cooling system (hence a regular water loss adding to circumstances that could have caused this HGF)
When hand fitting the main through bolts for measurment checks the vast array of resulting measurments was eye opening. Some bolts would go all the way to the end of the thread whilst three locked up early and were beyond service limits - renewed. (Wonder if the bolts that were free all the way had been torque correctly as obviously no stretch had occurred. Lends more thought to this being another symptom that lead to the HGF)
Finally and most interestingly for this thread was the fact that when I removed the inlet cam wheel something dropped onto the floor. Yes it was the roll pin which raised some concern. Of even more concern was the fact that when I removed the head and examined the cam I found a piece of the casting had broken away with the fracture going through the roll pin hole.
Clearly the lip around the cam wheel had been holding everything in place until I removed it. I found the broken piece of casting and staining indicated a longer term fracture. I imagine that this was caused by incorrect location of the cam wheel and then the bolt was tightened and it passed the loading through the pin into the cam which failed.
Of interest was the cost of a single replacement cam was little less than a pair from Kent, so a pair of mild cams have been fitted to see what they achieve. The head took a very light skim, which was cheap and simple since obly the cams and cam carrier has to be removed, following which a damn good wash out is needed.
Starting was fun with a slightly raised compression and cams that threw a big wobbly into the vac signal going to MEMS. It actually started quite easily but wouldn't run clreanly at below 1500 rpm for a couple of hours. Even then a 20 mile drive was needed to allow reasonable settlement of MEMS to the new parameters. I still suspect a throttle pot fault to be present to be sorted next week.
|Just to expand on Roger's comments re the roll pin, the only purpose of the pin is to locate the pulley whilst the bolt is being tightened. Once the pulley bolt is torqued up the pin plays no part - it's has no inherent strength. So the original problem has not been caused by a failure of the pin, but the failure of the pin has been caused by the bolt coming loose (i.e. incorrectly tightened).|
|be4 the thread disappears to the archives.|
Christof seams to be off anywere in warmer locations.
From his email to me he mentioned about powerloss over all. Than they measured app 15 degrees wrong (late) angle of the outlet cam. At last they found the pin crunched, but he wrote that the torque to the cam wheel bolt was OK.
Anyway, the theory due 'assembling failure' can be right cause I know from him about other works at the VVC some month ago !!
Worth to think about it and keep it in mind.
very interesting findings Rog - but also a bit worrying to say the least ! There is one thing that is unclear to me about this cambolt /pin thing : How does it look like after a failure ? Is the bolt still OK (ie. not head or other part sheared off, the bolt has simply unwinded ) or is the remains in the cam only a piece of theaded bolt WITHOUT the clamping head and hence a broken pin ? Having not yet seen the assembly in situ taken apart - what part secures the fairly heavy load between camgear and the cam itself. As said it is NOT the pin , only the torque of the bolt clamping the wheel to the cam then ??
Wishing to get the picture ,
regards , Carl.
i am just back and the guy, to whom happened the problem with the pin, too. In my case the pin was compressed. The pin is made of "spring steel" and if he suffer a big load he get compressed, I think.
In my opinion the pin has to transmit nearly the whole load from the sprocket to the camshaft. The torque of the screw to bolt the sprocket only presses flat surfaces together. There is no conical flange or so which could climb(?) both parts (camshaft and sprocket) together. Normally on other cars instead of a pin there will be used a key, a metal piece in shape of a half moon.
I could not absolutely exclude that the compressing would have been caused by a bad assembling. But I already then should have noticed incorrect timing of the camshafts. This was not the case. Nevertheless about 1000 miles after reassembling of the whole VVC-mechanism by myself, a sudden loss in power and uneven idling appears, caused by the compressed pin and the resulting incorrect timing. In my case I had only to change the pin and the car was driving well as before. Additionally I strengthened the hollow pin with a piece of a thread which fitted quite easily into the pin.
In my opinion the pin is too weak for the intended purpose. But I couldn't examine the real reason for the defect in satisfactory manner.
|Those roll pins are used on all Rover 16v engines (including T16) so are 'usually' enough for the job.|
The pin doesnt take much load until the bolt is loose.
The failure would have been the bolt first, then the pin collapsing.
Changing the roll pin for a piece of rod may be a worthwhile addition. (ill be doing this to mine now ive read this!!)
BUT its not the answer to the problem of the bolt un-doing. (loctite or similar may help, also adding "is the bolt done up" to your weekly checks may prevent it)
|:) nice it worked contacting Christof.|
Suppose we will necer know what happened at first. (Bolt or pin).
Anyway, I know of different types of this roll pins. And from out of the sight of a designer they should get used on less precise centering of two independet drilled parts.
BTW the right technical english spelling is obviously 'elastic dowels' or 'Slotted Spring Pins' (US) and 'coiled spring pins' (US)
(Copy and paste the link)
Interesting responces. I am a bit af a newbie with MG F's so please excuse my ignorance. I was told by me garage that the bolt was OK but the little pin was sheared. I had a look at the assmbly (I have the camshaft and sprocket) last night and could not really see how they fit together.
Are there any links to a workshop manual or detailed digrams.
On another note. I am interested to hear of weekly / dailyt checks on an F. What should I be checking and how often?
Thanks in advance
|As Drew said above the bolt usually fails first ,this can happen if the bolt is reused instead of being replaced, ALWAYS use new bolts and loctite.|
As a matter of interest does anybody know if Rover recommend these bolts are replaced when removed?
|I've never replaced the camshaft bolts - it's a big bolt for the amount of torque that's applied (can't remember what it is off the top of my head - 45 lbft perhaps?).|
Christof - there's no way the pin is supposed to take any loading. It's entirely normal for bolts to be in tension, relying on the force between two surfaces created by the tension in the bolt to transmit force from one component to another - that's how the crankshaft tranmits the torque generated by the engine to the flywheel.
|Mike you are right it is a big bolt for the torque loading but after witnessing the failure of this bolt(remember Sophie Ross's engine last year?) we asked the manufacturers (Atlas) to test 20 sets , we found the bolts failed very near to the required torque settings on their advice we have changed the specifications . They certainly would not recommend re-use.In fact they did not recommend this type of bolt for this application! However their recommendations doesn't mean that the engine manufacturers would take the same advice or recommendations as they have different parameters. I asked Rover for the calculated loadings on this component but they declined to offer this information.If anyone is in doubt ask Mike Coward for a look at his bill for the repair work on his engine because this bolt was not changed at the cambelt change by his local mechanic.If you feel lucky re-use 'em;-)|
Thanks for the responces, I spoke to the mechanic who fixed it last night and he says that the bolt had sheared. Obviously I have no idea whether it was changed or replaced previously.
I guess you could get them to change it with a new cam belt if you were paranoid.
|Blimey, thanks for that Mike. I know lots of people who have done numerous cam swaps, head rebuilds etc. on their Ks and none have ever replaced the camshaft bolts (nor experienced a failure - yet!).|
When you say you've "changed the specification" does this mean you sell an uprated bolt?
|Mike, yes the bolts are upgraded to a 12.9 grade steel unplated flange bolt(set screw) with self locking head,torqueis recommended @65Nm. For what they cost it's not worth risking using 'em twice :-)|
|I've just had my cambelts replaced (by SanSpeed - excellent service), but there was no talk of replacing the cam bolts. Is it necessary to remove the bolts to change the belts? |
|Hugo as you said belts I assume you have a VVC ,if this is the case then the rear belt replacement requires the front gear wheel and bolt to be removed ,the front belt can be changed without removing the gears /bolts but the bottom crank pully has to be removed.Hope that is clear 8-]|
|Going back to the failure I have encountered. It is a cracked edge from the front part of the cam casting, with the crack passing through the rollpin hole. In an assembled form there was no problem as the bolt thread was untouched and the torque was still very much apparent. Only on dissasembly did bits drop away.|
I find the testing resuilt very interesting. As a matter of interest what is the shear torque with the new bolts?
|If I remember correctly there was a recall a little while ago to remedy the rear cam sprockets coming loose on the VVC head. I currently have 11 VVC heads in my garage which have suffered failures of one kind or another, 5 of them have suffered loosening of the rear sprocket on the inlet side, this immediately causes the roll pin to take forces it's not designed to handle with resulting failure and mangled valves.|
|An update on the bolts! After stripping a new Steptronic/Stepspeed to-day we discovered the bolts have been changed to un-plated bolts but still the same strength steel also the cars now have the new steel dowels to locate the head so the later cars should have a better HGF failure rate.|
On another note(same car) I noticed a possible reason for HGF that hasn't been observed before and caused us to have an hour or so of head scratching! The head bolts on cylinders 3/4 on the front of the engine when screwed in to check them for length were binding and not screwing down enough on checking the threads they appeared to be under some stress 8-[ After checking the available thread depth it appeared that the bolts were in fact hitting the sump pan and if assembled would not give the correct torque between the head and block.The sump does in fact have a raised section in this area and is very near to the bottom of the bolt especially the one between cylinders 3 and 4 to the front.Solution was to shorten the bolt by 5-6 mm.The old gasket was fractionally thicker at this point indicating full torque hadn't been reached,the car had covered 7200Km.
Food for thought!
|>Food for thought!|
was this effect of to short thread in the block visible also at the bolts end in any way ? 'shining marks' or any scratches ?
Anyway, looks like always check the length not only by measuring the single bolt, but screw them to the block and measure than whether the height is equal, is it ?
I have a few questions for Dave and other´s involved in the K-serie engines. How come that this engine is the only one I have come across during all years as a car-maniac and DIYér that has NO washers (english?)under the cylinder head bolts ?? Looking beyond the torque settings and angeled settings - what figures in torque does the final settings give? When releasing the bolts one can easily use the torque-wrench "backwards" and get some indication... I am fully aware about the stretch moment in the bolts but clearly this does respond to some torque figure that possibly could be checked after about 60000km or any convinient interval.
best regards , Carl
|Dieter, the thing to check is the height of the head, say this measures 100mm, screw the bolts into the block before the head is fitted finger tight and measure the remaining height from block to bolt flange, the gasket will account for 1.5mm but ignore this for safty margin, if the remaining height is approaching the 97-100mm then it is time to investigate the problem , the bolts will leave a healthy margin on cylinders 1/2 as the deep part of the sump is below the danger areas, as I mentioned above, is on cyl 3/4 on the front two bolts where the sump is close to the oilrail/clamp plate. |
The bolts are approx 412 long with 72mm thread,the block is 282mm height and the oil rail is 25mm thick.The critical bolt is the front one between 3/4 cylinders because if the bolt is fitted to the block the measurement before it hits the sump is around the 99mm mark,from block to u/s of bolt head. So if you have a head skimmed and it is say 99.5mm when bolted in position there is a strong danger of this bolt bottoming on the sump and not stretching as it was designed.There is approx 72mm thread on the bolts into a 25mm plate so removing the 4/5mm will not affect the depth of thread in the plate as the bolts protrude 8-9mm below the plate into the sump area. I doubt there is a danger of the bolt running out of thread as the block and head measure approx 382 and the unthreaded section measures about 340 this would mean the bolt would have to stretch some 42mm!!!The ideal solution is to have bolts that measure 405mm long IMO. I hope this is clear enough but to summarise the bolt between cyl 3/4 on the front of the engine needs to have a safe margin of say 97mm protruding above the block face when screwed in finger tight.IMO.If this is NOT the case remove 3-5mm from the end of the bolt,ensure the threads are recut as this would affect the torque settings.
|Thanks a lot !|
Hope I never need the instructions myself but would like to put it to the HGF repair website to Rogers brief description if you agree.
May I use ? with credits and copyright, of course.
|Hmmm.........All the specialist skill you need to develope if you own a MGF!|
|Not really Mega this site is for enthusiasts that like to be informed and have a certain satisfaction in working on their cars , specialist skills are just that, skills required by a specialist, just like any other trade.|
Dieter use the information as you wish I hope it helps someone.
Dunno whether it helps. Was only one of 76.000 you found as trouble..... until now.
Anyway, makes the webside stuff more comprehensive and the bolts seam worth to be double checked if the head is off in any way.
|In reply to Hugh of London's query you should not need to remove the cam shaft drive wheels/sprockets when changing the cam belt.|
|OK, thanks for the replies. Assuming that the SanSpeed mechanics didn't crossthread the old bolts when they reused them, the tension in the bolts should be the same if they were re torqued to the correct value. So I think I can live with the old bolts being reused (although if I'd had the foresight to specify new bolts, I would have asked them to use them!).|
And then the question arises - what's more reliable, a proven old bolt, or a new one which has never been used....
Old cynic, me.
|The head bolts are 'flange bolts' which in common with a lot of modern fasteners have an integral washer, this simplifies manufacture/assembly and cuts costs, provided the underside of the head is lubricated then this arrangement is satisfactory. The stretch bolts are designed to give even clamping force over the whole head and stretch to give a force of around 55-60ft/lb. Th whole idea of the bolt 'stretching' is that it gives and maintains a consistent clamping force which should not need revision or checking.|
The bolts can be re-used up until their overall length exceeds the published figure, in practice this generally allows 3-4 re-uses.
>>If anyone is in doubt ask Mike Coward for a look at his bill for the repair work on his engine because this bolt was not changed at the cambelt change by his local mechanic.If you feel lucky re-use 'em<<
And John mentioned:
>>In reply to Hugh of London's query you should not need to remove the cam shaft drive wheels/ sprockets when changing the cam belt.<<
I guess I am feeling a little confused after reading this chaps. Are we looking at the difference in procedure between VVC and 1.8i or can the cam belt be changed without resorting to touching the cambolt on both engines??? :o§
If the cam bolt needs to be loosened/ removed, should the 5year/ 60k mile cambelt change be performed with a replacement of the said bolt as Mike clearly infers?
Thanks for the clarification
Although, I have never done it myself, from looking at the manual and as Mike says above in reply to Hugh, you don't need to remove the cambolts/gear for the 18i BUT you need to remove them to change the REAR belt on the VVC (the 18i has no rear belt).
|Thanks for that clarification Spyros :o)|
Guys, I am working on a 'MGF Recall' page to include the VVC cam bolt recall that is relevant to the information being passed here. Mike, Roger, Andrew are you all OK with me reproducing in part what you've all said?
|Spyros, again for purposes of clarification, is replacement of the rear cam belt bolt specified in the MG-service schedule? It seems pretty clear from Mike Cowards' previous post and Mike Satur's posts here that failure to replace the cam-bolt lead to the destructive failure of Mike's engine.|
I cannot find any mention of using new cam bolts in the work shop manual. Not even in the section about removing the cam gears. It just says "fit bolt ... and tighten to ... " .
What I find interesting is that the new manual I have (edition 7) has a bunch of warnings about timing belts that where not present in edition 3. For example it says the belt MUST be replaced if the cylinder head is to be removed.
|Rob, the cam gears do not have to be removed to change the cam belt on the 1.8 or VVC it depends on how each mechanic prefers to work, the bottom pully has to be removed and if the cam belt is slipped over the two top gears then over the crank gear there is no need to remove the gears at all, the gears have to be removed if the head is being removed as in a HG replacement because the cam gear cover is fastened behined these gears and onto the block/head. The rear VVC belt is fitted by removing the front gear wheel, there is no tensioner on this belt as it is quite short.Hope that makes it clearer.BTW I think MGworld is doing an article on this very subject next(?) issue.|
|I'll look forward to reading that article Mike.|
Thanks for that clarification. Basically from what I understand from what is being said here is if the cam belts are replaced as per Rover instruction (I presume that there is such a thing and MG technicians are specifically trained), then there is really very little risk of failure. If however you use an independent garage for the service, and the technician decides to remove one of the cams, there is potential there for things to go worryingly and destructively wrong if the cam bolt is then re-used- as happened in Mike Coward's case?
Jeepers... the worrying consequences of innocently doing things a little differently... :o(
if you like pictures in high resolution from mgf-net site for the recall documents, than let me know.
Mike Coward gave permission by email the other day and his from the picture collection is already on my HGF collection page in low resolution.
|The independent local garage followed advice from Windsors of Wallasey (Rover) and bought all the necessary parts for the cam belt change. Replacement cam gear bolts were not supplied since Rover use the old bolt when changing the belts :-/|
As far as I can see, the local garage did exactly what a Rover garage would have done.
I have no legal clout since the breakdown was a 'mechanical failure of the bolt' and (apparently) not the incompetance of the garage :-(
Also, the car did nearly 10,000 miles since the cam belt change, 5 months prior to having the engine trashed.
Southport (when in the UK)
|>>if you like pictures in high resolution from mgf-net site for the recall documents, than let me know.<<|
Thanks Dieter, that'd be great. Either the pix or hyperlinks would be ideal :o)
Thanks Mike for permission to use the pictures for the 'Recall' page- much appreciated :o)
Feel free to use the info.
|In my opinion, there are a couple of reasons for the failure of this bolt in Mike Coward's engine: the bolt was over tightened setting up stress fractures in the metal and leading to it eventual failure, couple this with the fact that the 'old' bolt was used which had been stretched the first time around . The surface treatment of the standard bolt is a zinc finish by the process of zinc plating the threads become rough and surface damaged, have a close look at a unused bolt, this can lead to incorrect torque readings and a relaxing of the bolt during service with obvious results. I believe the zinc process also embrittles the bolt which could lead to these types of failure, shearing and relaxing. During independant testing the bolts failed at quite a large range between the highest and lowest, indicating a unsuitable specification for this application. If the bolts are used with a locking agent there is less risk of the bolt failing. It is important that these bolts are replaced with un-plated bolts of the correct strength and are degreased before use. |
The VVC seems to be more prone to this relaxing, this could be due to the greater torque loading of the cam wheels and the 'imbalence' of the VVC assembly.
This thread was discussed between 19/11/2001 and 08/12/2001
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