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Jim Mock Cams and chain / engine rattle? 

 

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Posted: Fri Aug 15, 2008 11:15 am 
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balizticbobo wrote:
Using a reground cam won't move the cam closer to the crank...
But skimming the head will.
Please feel free to correct me if i'm wrong, but aren't most Dev5's out there complete engine rebuilds? Therefore, the block deck would most likely have also been skimmed, a s**t also skimmed off the head, and a timing chain that is now way too long. Which also means that the tensioner has run out of travel, and cannot take the slack out of the chain. Chain is now free to rattle about and slam into the guides and simply destroy everything in its path. How would you like being whipped thousands of times every minute by a hot oil soaked timing chain. How many kms would you be able to handle it for before you finally broke?
The only way I can think of checking for this is to run the engine with the rocker cover off, also preferably over an unliked neighbours front lawn! And watch the timing chain to see if it's free to shake.

If so, try a new tensioner, it may also be necessary to modify the tensioner with the addition of a spacer JB WELDED onto the end, or modify the guide itself.

Remember the tensioner has the same operating characteristics as a hydraulic lifter. When it's run out of travel, it's going to make noise. Noise means increased wear = BAD!

I have the Head, Cam and Vernier gear off a complete JMM DEV5 that spat the chain and guides, also cracking a piston and bending some valves.

VL's are notorious to snapping off the cam belt tensioner when fitted with a decompression plate. Belt is too short = massive load on tensioner in fully released position.


Now there's a smart man, got the answer in the first go.

I have zero noise and problems with my Dev 5 cam, but only after I have set it up properly and taken into account its and my engines characteristics.
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Posted: Fri Aug 15, 2008 12:16 pm 
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So, what can I do to remedy my situation?

Different cam?

Different head?

 

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Posted: Fri Aug 15, 2008 12:51 pm 
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Shorten the chain if its too long.

I have added shims under the tensioner spring to keep a tighter tension on the chain. Plus it ensures it will push the tensioner out a little further to keep adjustment.
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Posted: Fri Aug 15, 2008 12:58 pm 
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I would suggest different cam, especially if you are goinf forced, you don't need the lift the dev 5 has, I would suggest something from wade, and spend the extra money and get a billet cam, Not suggesting there is anything wrong with a regrind, I run one myself, BUT if I was gonna blow my motor I would be looking for a billet, wade can provide this for you. there a few guys running blown motors with wade cams, they have one that suits a blown motor in their range too.

Next I would be looking at the head trying to find out how much was skimmed off the head to bump up the comp ratio. my understanding is that JMM skims the head, and pulls meat out of the ports, and cuts out the valve guides to what they deem a minimum amount remaining.

I would suggest you get BPT to have a look at the head, they will not be able to see too much with it on the car though, I would say maybe drop the exhause manifold and have a look in, If you have a decent digital camera try and get a clean shot of the inside of the port and post it on here, someone will be able to make an educated decision as to how much has been taken out and if it remains suitable for turbo'ing. as long as the head has not had too much taken off it, it should still be suitable.

The cam I would definatly change, as previously suggested, yes you are definatly suffering from backlash. change of cam will fix this 95% of the time.

 

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Posted: Fri Aug 15, 2008 1:24 pm 
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This is a slight bummer, since I am trying to keep the 40-50 rwkw advantage that the JMM gear gives me ...and maintain that advantage when I boost too.

I think I'm gonna leave her in BPT's capable hands, and see if they can sort something for me ...even if it takes a little modification or engineering to achieve it.

Maybe they can shorten the chain, or shim the tensioner as Arm79 suggested?

Can someone post the link / model no. of the Wade cam I should be looking at?

 

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Posted: Fri Aug 15, 2008 6:14 pm 
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Another suggestion ...DOUBLING-UP on my AU MLS head gaskets?

 

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Posted: Fri Aug 15, 2008 10:02 pm 
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see if BPT can modify the tensioner for you so it puts the correct tension on the chain.

 

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Last edited by fritzz on Fri Aug 15, 2008 11:40 pm, edited 1 time in total.

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Posted: Fri Aug 15, 2008 10:06 pm 
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arm79, do you have pictures of the shims you have put on the tensioner?

i dont believe this problem is specific to JMM cams, it will happen with any cam that has a steep profile when using stiff valve springs.
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Posted: Fri Aug 15, 2008 10:25 pm 
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fritzz wrote:
see if BPT can modify the tension for you so it puts the correct tension on the chain.


Thanks mate ...I'm pretty sure that's what they'll do.

Jim Mock suggested that they use a couple of washers to do just that.

 

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Posted: Sat Aug 16, 2008 12:25 am 
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galapogos01 wrote:
arm79, do you have pictures of the shims you have put on the tensioner?

i dont believe this problem is specific to JMM cams, it will happen with any cam that has a steep profile when using stiff valve springs.


No I dont. They were just washers about 1mm thick. Cant remember if I put 2 or 3 in there. My understanding is the chain should have no more than 2mm deflection on the cam sprocket when its resting. So I followed that guideline.

And yes, its more a cam profile and spring issue than the cam. Could happen with any cam.
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Posted: Sat Aug 16, 2008 12:43 am 
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balizticbobo wrote:
Please feel free to correct me if i'm wrong, but aren't most Dev5's out there complete engine rebuilds?


Nope, they're just reco head packages.

 

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Posted: Sat Aug 16, 2008 1:46 am 
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DEV 5 is..

"DEV "Street-Fighter" Headers (Extractors), Modified Cat, 2.5" Hi-Performance mandrel bent exhaust system, Hi-Flow Intake Kit, DEV5 Cam kit, valve train modifcations, Vernier adjustable Timing Gear. "Race-Series" Head, extensive porting and head performance alterations to race standard, compression increase and Special valve springs. All installed with new gaskets & seals. Top class Performance Street package also suits Street / Strip use with excellent fuel economy"

 

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Posted: Sat Aug 16, 2008 10:02 am 
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arm79 wrote:
No I dont. They were just washers about 1mm thick. Cant remember if I put 2 or 3 in there. My understanding is the chain should have no more than 2mm deflection on the cam sprocket when its resting. So I followed that guideline.

And yes, its more a cam profile and spring issue than the cam. Could happen with any cam.


thanks mate.

where did you stick them? you put them between the removable tensioner part (for want of a better name) and the piston (the only place I can think to put them), right?

I suppose that wouldnt interfere with the spring lock mechanism as when you unlock the tensioner (which springs out where the washers would sit) you have the removable part out.

Might give this a try. My old tensioner was jammed (metal filings around the piston, had to hammer it out), and I used to get a clack only when cold and only from 1500 to 2000rpm. Now with a new tensioner it will do it when hot also - but its a lot less noticeable. 1mm of washer might be enough.
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Posted: Sun Aug 17, 2008 5:36 am 
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galapogos01 wrote:
arm79 wrote:
No I dont. They were just washers about 1mm thick. Cant remember if I put 2 or 3 in there. My understanding is the chain should have no more than 2mm deflection on the cam sprocket when its resting. So I followed that guideline.

And yes, its more a cam profile and spring issue than the cam. Could happen with any cam.


thanks mate.

where did you stick them? you put them between the removable tensioner part (for want of a better name) and the piston (the only place I can think to put them), right?

I suppose that wouldnt interfere with the spring lock mechanism as when you unlock the tensioner (which springs out where the washers would sit) you have the removable part out.

Might give this a try. My old tensioner was jammed (metal filings around the piston, had to hammer it out), and I used to get a clack only when cold and only from 1500 to 2000rpm. Now with a new tensioner it will do it when hot also - but its a lot less noticeable. 1mm of washer might be enough.


I ended up putting them between the left end of the spring and that little removable metal thing (f**k if I know what its called) that the allen key goes into.

I didnt want to put them down the other end for fear of them getting crushed or damaged by the piston and outer retainer and actually causing the tensioner to lock. But then I didnt use perfectly sized washers. I couldnt find them.

But it seems to have done the trick for the past 6 months.
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Posted: Tue Sep 23, 2008 11:00 pm 
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mark, did you get anywhere with this?

after leaving mine rattle for 1000km (with a new tensioner - markedly worse than when the tensioner was jammed open), its gone and broken the passenger side guide on me. so its back off with the timing cover to fit a new chain and guides this time.

hope like f**k it doesnt do it again after this - would appreciate any more advice on shims/springs in the chain tensioner or other tricks (i am thinking something attached to the guide where the piston runs?) otherwise will use the washers mentioned above...

Jason
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