rod bearings and crankshaft drag

[bill jones]

-When we used to use timing chains we had the "tight" chain problems similar to what you have, where it would lift the crank up off the bottom of the bearing.
-This sometimes gives you a noise that about drives you nuts from the compression pulsing the crank nose up and down.
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-Same thing happens when you tighten up the alternator belt.
-I have seen where the top of the front main bearing (biased towards the alternator) on daily driven street engines has shown wear.
-Personally I would probably machine up a slightly smaller spacer or modify the spacer so that I could adjust the tension like the Danny Bee BB Ford belt drive, make use of an eccentric.
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-I don't see how it messes up your clearances at all, it just means that the belt will get tighter when you start the engine and get some downforce from the combustion pushing on the rods.
-The main bearing clearance is still there, it's just that the crank isn't sitting dead in the middle of that clearance when at rest.
-The crank can move around inside the bearing that .002" clearance like when you roll the engine upside down the gravity always holds the crank down, but now you have the belt acting against the natural gravity.
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-I don't see where it's a major issue especially now that you have recognized the problem, might just create a little more wear on the front cambearing.

[bill jones]

-Speaking of the needing a little extra rod bearing clearance, I have gone thru that on more than one occasion, where I had select fit say one shell at a time of a .001" oversize to get the exact .0004" or .0005" clearance I wanted and that is a very tedious job.
-What I would do is to get a set of eight .001" extra clearance bearings and that gives you 16 choices on the first rod and 8 choices by time you get to the last rod by using only one of the oversize shells in conjunction with the standard bearings.
-Be sure to check the radius's of the crank to the bearing chamfers for interference.

[JOHNZ]

Thanks Bill, I will read and comprehand your post later....my 4-year old is draging me outside in 40 deg. weather to play starwars!!!

The Comp belt is made by Danny Bee, or the other way around....they are very similar if not exactly the same.....here is a pic of it...

http://store.summitracing.com/default.a ... 0&x=19&y=8

Thanks again for your help...

[ChrisU]

I would sell the the Comp piece and get a Jesel without an idler pulley. I do all I can when building an engine to keep from using an idler pulley. There are many instances where I have heard of idlers failing, not necessarily a comp unit, as I would rather not use this site to bash products.

Generally, the whole reason companies use an idler is to use a standard belt from a supplier that is generally available, so they don't have to pay for the design of a new, custom belt.

Chris

[JOHNZ]

thanks Chris, don't some of the Jesel belt drives use tensioners as well?

They make things tight, but I would think once the engine is running the belt will loosen up some...

[Adger Smith]

I have had to throw those rollers up in the lathe & turn them smaller in some cases. Comp sells different sizes too. you need more thrust clearance too. I usually go between .010 & .014. .007 will bind when it gets hot. Call Tim Cole @ Comp cams. He & I run Splayed valve V-6 engines that are similar. They are hard on belt drives & the Comp seems to last a little longer. I have customers that run both Comp & Jesel & the roller on the Comp seems to take the "FLAP" out of the belt & it lasts longer. The design of the Comp belt seems to stay in the gear a little longer than the Jesel. Never tried to measure the pitch, but it could be the pitch of the gear/belt that causes the extra load.