Rv8 - Chasing a knock - distributor removed
Discussion
Since going to coilpacks, my Serp 4.6 seems to have developed a whirly knocking that could appear to run at half engine speed. No noticeable effect on performance and listening around the engine with timbers and tubes etc hasn't located it
After seeking the wise counsel of V8D, had a delve in the sump yesterday and popped a few caps off with no obvious shell damage evident, bores and cam also seem in good health from what I could see from underneath. No metallic debris in the sump pan. I'm just wondering if the dizzy on this engine serves to locate the cam or whether some other retention system operates? If not, could cam float conceivably be the cause (and is there a fix short of reinserting the dizzy)?
Prolly clutching at straws but worth a Q as I'm running out of ideas...
After seeking the wise counsel of V8D, had a delve in the sump yesterday and popped a few caps off with no obvious shell damage evident, bores and cam also seem in good health from what I could see from underneath. No metallic debris in the sump pan. I'm just wondering if the dizzy on this engine serves to locate the cam or whether some other retention system operates? If not, could cam float conceivably be the cause (and is there a fix short of reinserting the dizzy)?
Prolly clutching at straws but worth a Q as I'm running out of ideas...
I'm not an engine builder, so this is just based on what I've heard and read from people who know better. The people at V8D would be the ideal ones to ask.
As far as I understand it, the cam will have a different nose depending whether it's serp/intermediate or pre-serpentine. The dizzy drive would put a gentle end-load on the cam and it's entirely possible that you would get cam walk with it removed, unless the cam has the right nose (or a spacer button added etc). Although I haven't ever heard it, cam walk has been described as causing a sequence of very heavy knocks that happen sporadically as the cam floats out of position and then gets knocked back.
If you have space to refit it, I would be inclined to reinstall the dizzy and see whether that stopped the noise. If it does, I'd say it confirms your diagnosis.
As far as I understand it, the cam will have a different nose depending whether it's serp/intermediate or pre-serpentine. The dizzy drive would put a gentle end-load on the cam and it's entirely possible that you would get cam walk with it removed, unless the cam has the right nose (or a spacer button added etc). Although I haven't ever heard it, cam walk has been described as causing a sequence of very heavy knocks that happen sporadically as the cam floats out of position and then gets knocked back.
If you have space to refit it, I would be inclined to reinstall the dizzy and see whether that stopped the noise. If it does, I'd say it confirms your diagnosis.
All the 4.6 blocks I've seen had a cam retaining plate (just different versions int-sagem-bosch I guess???), if it hasn't been fitted well... I thought all V8D cams come machined ready for the retaining plate so fit in any of the blocks or front covers.
Do you not know what went into the engine? All the intermediate TVR front covers I've seen under had a cam retaining plate, even with the dizzy's fitted - but not knowing the origin of yours Gary?...
Do you not know what went into the engine? All the intermediate TVR front covers I've seen under had a cam retaining plate, even with the dizzy's fitted - but not knowing the origin of yours Gary?...
Ok, cheers... it's a V8D sourced unit with an H404 but I've never had the front cover off. TBH Rob was good enough to spend quite a while having a good listen around it (sorry you got a belt Rob 
) and didn't suggest this although he did comment it could have been coming from the cover area (really difficult to tell), just me thinking through other possible after not finding anything obvious in the bottom end.
Next step will be to strip out the valley so I might be able to see whether it's a possible from there...
ETA no longer have the dizzy to try and the power steering pot now lives there
) and didn't suggest this although he did comment it could have been coming from the cover area (really difficult to tell), just me thinking through other possible after not finding anything obvious in the bottom end.Next step will be to strip out the valley so I might be able to see whether it's a possible from there...
ETA no longer have the dizzy to try and the power steering pot now lives there
Edited by Pupp on Thursday 13th August 08:57
The pre serp engines did not have anything to locate the cam shaft .. a teflon button was added to some to stop the cam moving fore and aft.
All serp engines have the locating plate..
The noise could be the cam chain.. it could be old and worn. Also - there is not a lot of lubrication in there - I believe..
If it has the morse type chain - that can wear quickly - stretch and break off a tooth.
All serp engines have the locating plate..
The noise could be the cam chain.. it could be old and worn. Also - there is not a lot of lubrication in there - I believe..
If it has the morse type chain - that can wear quickly - stretch and break off a tooth.
350Matt said:
Being as you've got the sump off you should be able to look up into the timing chest I believe?
Small torch and dentist's mirror might be the order of the day?
Had a go Matt but there's not enough access to have a decent look. Sump's back on now; I'll have a go from the top...Small torch and dentist's mirror might be the order of the day?
Ok, after stripping out the valley stuff, the one cam lobe that I couldn't see from underneath (cyl 7, second lobe from the back) is half gone. All the rest seem pretty fine really and the motor has about 45k on it. No idea whether this would account for the noise of itself but as the cam needs changing, I'll whip it out tonight and see what's occuring behind the front cover. Anyone able to point me to an image of what this retainer arrangement looks like?
I'm assuming there's no huge pitfalls inside a Serp front end to make this (or reassembly) a horrendous task?
I'm assuming there's no huge pitfalls inside a Serp front end to make this (or reassembly) a horrendous task?
Pupp said:
Anyone able to point me to an image of what this retainer arrangement looks like?
Its like a horseshoe shaped plate with 2 bolts that hold the cam in place, you'll see it behind the timing gear when you pull the chains & sprockets off. If it's there it will be pretty apparent. The v8 overhaul manuals spec all the tolerances to check for cam float (& the oil pump?), they do suggest replacing the retaining plate if it is worn, but I would guess that requires uber mileage? There are a few different slightly retainers IIRC although they all look very similar (just don't line up when you try to fit them, as I found out after I mixed some parts up in the washer
)
Well, that's cleared all the gumph off the front so I can have a clear go at the timing cover next session (who specced all those screws for a water pump? 
)... sorry for all the Q's but am I correct in thinking the sump can be left in situ if the front fasteners are removed? Guess the oil filter should be spun off to avoid sloppage?
)... sorry for all the Q's but am I correct in thinking the sump can be left in situ if the front fasteners are removed? Guess the oil filter should be spun off to avoid sloppage?Pupp said:
Well, that's cleared all the gumph off the front so I can have a clear go at the timing cover next session (who specced all those screws for a water pump? )... sorry for all the Q's but am I correct in thinking the sump can be left in situ if the front fasteners are removed? Guess the oil filter should be spun off to avoid sloppage?
You can leave the sump in situ, but unless you have completely drained all the coolant from the block you may get some fall when you remove the timing cover. )... sorry for all the Q's but am I correct in thinking the sump can be left in situ if the front fasteners are removed? Guess the oil filter should be spun off to avoid sloppage?Also, even with the front sump studs removed , it isnt easy to remove and refit the front cover without damaging the sumpgaset.
Ant. said:
Pupp said:
Well, that's cleared all the gumph off the front so I can have a clear go at the timing cover next session (who specced all those screws for a water pump? )... sorry for all the Q's but am I correct in thinking the sump can be left in situ if the front fasteners are removed? Guess the oil filter should be spun off to avoid sloppage?
You can leave the sump in situ, but unless you have completely drained all the coolant from the block you may get some fall when you remove the timing cover. )... sorry for all the Q's but am I correct in thinking the sump can be left in situ if the front fasteners are removed? Guess the oil filter should be spun off to avoid sloppage?Also, even with the front sump studs removed , it isnt easy to remove and refit the front cover without damaging the sumpgaset.
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