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308 timing chain stretched >15,000 km
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Hi guys,
I am just putting a fresh bottom end in my motor.
anyway
i put a new rollmaster double row chain 13,500 kms ago, i went to trasnfer it over to my new bottom end and noticed there is at least 10mm inflexion in the chain slack.
I cant remember how it was new, but this appears way excessive.. particularly as another OEM timing set on the changover motor appears to have less stretch (apparently 80,000kms old).
now my question is.
1) is this stretched or normal???
2) why is it so poor? i drive it gently.
3) would it have anyhing to do with consistenly breaking rocker gear?
4) WTF do they not run timing chain tensioners, I can move the cam without the crank pulley moving.. ie there is so much play?
any advice, past experience with timing chain stretch?
Cheers
Ed
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Holden originally built their homegrown V8 with a timing chain adjuster. It was just a rubber pad on a steel carrier that bolted to a boss to the RH side viewed from the front. It was deleted some time in the early 70's as it wasn't deemed necessary anymo |
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oh ok, so its a case of wide tolerances here.
I do have the threaded holes in each motor for the tensioner, although have never seen a tensioner.
i bought the roll master 9 key way timing chain set (this is the one which is nicely stretched now) so
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I've probably got some old chain tensioners off old motors at home somewhere. I can COD post you one if you like. I think they are just held in by 2 x 3/8AF set screws with star washers, just like sump screws and the tensioner simply has slots to adjust c |
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Hi Ed.
This comment set my alarm bells ringing,
"3) would it have anyhing to do with consistenly breaking rocker gear?"
You shouldn't be hurting rocker gear. Holden rocker gear is pretty durable for street use, with a stock or mild cam. If you'v |
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Hi Dr Terry,
I am worried too.
the cam is a very mild grind from COME. I deliberately kept the lift mild with just street cruising in mind. The heads were fully reco'd by Terry at Dominator so I have faith these are OK.
the lifters were new it
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Ed.
Don't mix the lifters up. If you have they will have to be replaced. They must go back on the same lobe in the same engine.
To be honest I missed the breaking rocker gear text, so i'm glad Terry raised it. I'd be carefully checking for spring bind. |
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Hi Guys,
checked the cam timing on the weekend.
perfectly spot on, reached spec on the cam lobe lift and centrelines for intake and exhaust were dead on spec.
looks like the cam chain is always that slack and is normal.
checked the lifter prelo
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Byron,
yep all the rockers, pushrods, lifters were laid out in order.
Cheers
Ed
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Did you use new lifters though? You shouln't re-use lifters in another block, even on the same lobe of the same cam.
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Thanks for the advice Byron.
Will now go and get some new lifters.
Do i have to observe the same 20 minute break in for new lifters?
im assuming so as the contact surface would need to be work hardened.
Cheers
Ed
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Yes. Also double check with your engine builder as well. It never hurts to get at least 2 opinions.
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308 timing chain stretched >15,000 km
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