74x92 rebuild

[1432]

Hey guys,
Long time reader , lurker or what have you...lol

I'm in the process of rebuilding my engine and ran into a problem with the crank counterweight hitting the cam lobe and wanted some suggestions on what route to resolve this issue. I do have another cam on order and it may clear the counterweight but if not what would you do?

Clearance the crank, then have someone rebalance?

Clearance the cam lobe?

Thank you in advance.

Video of issue...

http://youtu.be/nkf97zFJpNQ

[Marc]

You say this same combo was together and running...the ONLY way that could've been possible is if you now have the cam misindexed. I see you have one of those "Dial-In" cam gears. I'm not a fan of their cams, they all have excessively long clearance ramps which bleed compression and limit seat time so the valves have less chance to transfer heat.

Look at the timing mark on the gear - it should be lined up with the slot in the end of the shaft.

I once had a Scat crank that had this problem (and it was only a 69mm stroke) and a cam with smaller base circle was out of the question for the engine I was using it in - I had the counterweights cut down and then the crank rebalanced.

[1432]

Hi Marc, thanks for posting...

I have triple check to make sure the cam to crank is indexed correctly, but will follow up with some pics. This is exactly how the engine was ran prior to me tearing it down. I was very surprised to see the rub/grind marks on both the cam and crank after mocking it up. The crank will pass the cam but needs to be forced.

Now I just need to figure how to load them pics.

[Marc]

viewtopic.php?f=18&t=127818

[1432]

Thank you again Marc for you help.

Here is what I'm looking at...

Crank gear dots lined up with cam




Then, cam gear orientation on cam.






So, am I missing something or do I need to clearance crank/cam?

[Marc]

Looks correct - incredible that it ran that way without problems before now, normally one allows ~.020" of clearance to allow for case & crank flex and bearing wear - and you have less than zero. Hopefully the new cam has a smaller base circle and/or less lift.

[1432]

I know it's crazy it ran that way. Well, I do have another cam on order (w100) and hope that the lobe clears the counterweight. I'm going with the small cam because I will be turboing this engine and wanted good idle/spool up of turbo.

Would I be able to use that "dial in cam" gear for the new cam or should I just purchase a new cam gear?

More pic of damage...

Cam lobe wear on left hand side.




Crank counterweight wear.

[1432]

Ok, not much to talk about. I contacted the supplier last week and was told about two weeks out before I have my parts. I'm mainly waiting for the connecting rods and cam to get this engine mocked up. Again, I'm hopeful that the new cam will clear the crank counter weight.

I was in the garage looking for something to do besides clean up and thought I could make a crank holder for assembly. I know a lot of guys just weld a flywheel gland nut to their engine stands, but didn't like the height of where it put the crank. So I looked at the scrap metal that I had and this is what I came up with. I used a piece of angle iron and cut it in half then welded the two halves together to make a square tube. Then welded the gland nut to the end of the (now) square tube and now I can mount my crank up higher in my vise. I know it's not a big deal, but I need something for assembly and more then that, just bored.








A video of this circus act: http://youtu.be/yLbwzfZ9k0c

[art.b]

Nice tool! I think I'll make one to!

[1432]

Thanks Art, I can't take credit for it though. I've seen others go this route and liked it myself.

[1432]

I received the new camshaft, connecting rods and some misc. parts that I've been waiting for to move forward on this build. I have to say that I'm very pleased because I didn't expect these parts for another week. I can now start the mock up of this engine.

So, I put the cam gear on the new cam (W100) and installed to see if it would clear the crank counterweight and it did! I took a measurement between the two parts and it came out to .012 gap. I decided to take off a little more material on the crank counterweight to end up with a total of .020 gap between the cam and crank. I don't plan on having the crank rebalance because the upper rpm range of this engine will only be in the low 5000 range and feel the material that was remove is insignificant.


I cleaned up the area that was hit by the previous cam and then filed another .008 from the highest point on the crank, between the two black lines.




Now here is the .020 gap between the crank and cam lobe furthest to the right.




Video of new parts and cam mock up: http://youtu.be/_BWcb1pTatk

[Marc]

Now that looks better!

[1432]

Thanks Marc, I'm very happy too!