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Hi guys forgive my ignorance but I don't have a great understanding of how heads work. I am thinking of purchasing a 2000 bus with a brocks big bore and big cams. The owner has told me that it chews through the buckets?? Related to cams faster than it should. Is this a common issue for big bore big cam engines? Is this a symptom of a bigger issue? Any help would be great as I'm pretty interested to buy this for a hotrod street/drag bike. Thanks.
Regards
Dan
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betting it has something to do with stiffer valve springs = more friction in valve train = more wear on rubbing surfaces.
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I think its due to the size of the lobes rubbing on the edge of the buckets which wears the hardened surface off. Stock cam lobes wont touch at the edge of the buckets.
There is no strong performance without a little fanaticism in the performer
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I found out a bit more info. I think The cams are .368 intake and .388 exhaust I'm going to try and get a look at it this weekend. I'm pretty keen to be honest.
Regards
Dan
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So changing valve springs........is it hard?
Regards
Dan
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Head off, and buy a valve spring compressor kit from ebay, and a small magnetic screw driver
the buckets will either be getting damaged from the cam material incompatable with the bucket
or too light a spring causing valve float
or too tall a spring on compression coil binding and wiping hard
or the valve guides not pushed deeper on a hi lift cam causing the same problem as coil bind
or dry startup/no run in on a fresh build, new cams need running in usually initially with a moly grease on install, then fast idle for 10 mins, 2500rpm or so
shutting down when the temp gets hi and restarting once cool
good heavy duty springs should not cause the problem
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Hi Maj,
thanks for the reply. From what the guy has said the valve springs are 70lb units that are on the brocks website which i think are carpenter items? with the cams being .386in and .388ex i didnt think that was that high a lift so i had assumed the springs where too heavy and causing the issue.
How would i know if the Cams are incompatable with the bucket? they are OEM buckets from what i know and the cams are the brock cams up on his website.
From what ive been told its only happening on the exhaust side does that change anything?
If it was from no run in or dry start is there signs to look for on the cams to indicate this?
Thanks again.
Regards
Dan
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buckets and cams would show scoring or some roughness if it were a dry start, usually when that happens it just dishes the buckets real fast,
i use 70 lb springs on the big boost turbo stuff , but with smaller cams , never had an issue with too heavy
better off with springs that are too heavy than to light
probably mentioned this before but an analogy of big springs
put your finger on a bench and rest a hammer on it, then a bigger hammer , not necessarily uncomfortable with either
now lift the light hammer a half inch and drop it , bet it hurts
valve train is like your finger, get valve float and it will hurt something
Probably the only way to realy be sure what the issue is would be to strip the head and measure everything
i thought .400 lift or so more likely to cause guide clearance issues but still only guessing without measurement
and if it all measures out ok then a different brand cam may be needed ???
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Thanks Maj your a champ. I pick it up sunday morning so i will probably ride it round for a week or so until its sorta out of my system and then ill start digging into it and see what the go is. Thanks all for your replys its certainly given me plenty of ideas to try and tackle it.
Regards
Dan
CAM S HAYABUSA .395/.378
-----------------------------
SHIM V .015 SET OF 16 BUSA
or
SHIM V .030 SET OF 16 FOR BUSA
or
SHIM V .060 SET OF 16 BUSA
+
SPRING S V HAYABUSA 99-11 47#
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yeh Dan I think I know the bike. I have heard of it happening on another all motor busa also
There is no strong performance without a little fanaticism in the performer
70lb is far too much spring pressure for those cams.
Around 50lb is a better number unless your drag racing and pulling your motor to bits every 5 races
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hey Horndog any idea what caused it on the other all motor?
Hey gruntmax thats what i had initially thought aswell. Maj added some other possible issues so i think to start with i might order some APE 47lb springs and some shims(upto ~50lbs) maybe some of the shorter guides and just put them in see how it goes, relatively inexpensive, makes me feel better and it eliminates a number of the possible issues eg too high spring pressure, too low a spring pressure, to long a spring, guides not low enough. at the time i will also have a good look at all the buckets and the cams see if there is any sign of an issue with them and if there is ill replace the cam and affected buckets and make sure i use a very liberal application of assembly grease and give it a run in like Maj suggested. hopefully ill get away with just springs and guides.
I have also been thinking about oil and whats best to use given the extra displacement/heat. any ideas?
Regards
Dan
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