Question about crankshaft balancing after knife edging

Road-race engines and ancillaries - general discussion
Post Reply
gazzol

Question about crankshaft balancing after knife edging

Post by gazzol »

Hello and thank you for taking the time to read this question.
I have started to build a BMW 3.5 straight 6 engine and I have made some inquiries with regards to having my crankshaft knife edged at a local engineering firm. I then made some inquiries with a company which undertakes balancing. I chose this company on the basis of my perception of their reputation (I cannot say too much in case I give away their identity) and the person I spoke to (the owner) proceeded to warned me about removing too much metal as it may then be impossible to bring the reciprocating mass back into balance. Obviously this person then proceeded to tell me that they would be only too happy to undertake this work for me thus guaranteeing that I wouldn't end up with a pile of junk. The cost would have ended up in the region of £600 which if I'm honest seemed a little excessive. I have my suspicions about what this person was saying but I'm no expert.
So is it possible to remove too much metal from the balance weights and thus ruin the engine?
Thanks in advance
gazzol
robert kenney
Posts: 161
Joined: July 11th, 2007, 2:23 am
Location: La Verne Calif, USA (A)
Contact:

Re: Question about crankshaft balancing after knife edging

Post by robert kenney »

On an in-line 4 or 6 the crankshaft needs to remain dynamicaly neutral when spun by itself. The recip. masses on an even count inline engine dynamicly offset each other. Any machining that will not remove material in a symmetrical manner will need to be corrected but there is a method to accomplish this. Any balance shop will have this knowledge.

When crankshaft needs more counterweight for either knife edging or other reciprocating mass changes, often "Mallory" (machinable heavy metal like mass of carbide) is inserted perpendicular to the counter weight face into drilled holes. Done every day when a V type of engine is stroked in order to offset the larger effective bob weight calculation.
Robert Kenney # 111
gazzol

Re: Question about crankshaft balancing after knife edging

Post by gazzol »

Thanks for taking the time to reply Robert. I have since spoken to two people who have advised against knife edging the crank so the question is redundant now.
Thanks once again.
gazzol
Post Reply

Who is online

Users browsing this forum: No registered users and 35 guests