I'm doing a rebuild for a friend of mine on an 85 12a for his home built Lotus Super 7. And everything looks great after initial tear down. The only thing that raises an eyebrow for me are the rotor bearings.

I should preface this by saying that the engine was running strong before tear down, but did have some smoking at high RPM's. The Oil Control rings were shot and are being replaced with a good used set.

The bearing surfaces have some copper showing through but no scoring that can be seen or felt, even with a fingernail. The E-shaft journals are nearly perfect as well so there's no signs of an oil failure other than the smoking.

The build itself will just be a medium sized streetport for daily driving and some track days (autocross not drag).

I will try to post some pics this evening but wanted to see what you guys think, I'm a bit of a perfectionist so I have to pull the reigns on myself when trying to keep a build under a budget. Just wanted to get your guys opinions, how much copper is too much? Or should I just run with it, since it won't be a 10k rpm monster?

 

Post the pics. BUt the answer to your question is a personal one. The appropriate answer is to replace the bearings; however, if the engine is on an economy budget and had no major issues prior to teardown, it should be okay. But lets take a look at the pics.

The scoring is the issue, and it sounds like youre okay.

 

Check the clearance between bearing and journal per the FSM.

I personally wouldn't use bearings showing asymmetric wear (copper showing some places but not others) unless the copper was only showing slightly at the bearing seam, but the clearance check is the crucial number. Everything beyond that is a judgment call.

 

As DivinDriver states, you'll need to first establish the actual clearance from the bearing to the journal surface.

THEN and only then, will the bearing become either "clearance is too loose, i need to replace it" to "clearance is ok, but the copper showing through still concerns me" type of situation.


From my own experience, any copper showing is a good reason to replace the bearings even if the motor did not exhibit and other issues.

It is very much a toss up when it comes to the budget builder.....
because you never know.... the worn bearing can eventually destroy the rest of the motor. But then again.... a new bearing could have the same effect if the rest of the engine is not checked and double checked.


I would venture out enough to say that i would at the very least check ALL the tolerances on the engine. irons, apex seal grooves, side seal grooves, eccentric shaft etc etc...

 

thanks for the input guys... going to checking tolerances in the next couple days.... I'll let you know how it goes.

 

If they're not scored, they are probably okay.

 

good oil pressure is a must. i'd replace them, but that's just me. gl with the build and let us know how it goes.

 

+1. IMO measuring everything really removes the need to make judgement calls...

copper showing is ok, but the bearing must be round and be at the right clearance

 

Bearings in general will last 2 rebuilds unless there's been an oiling issue or severe over heating. In most tear downs the copper will be showing at the bearing seam and the exposure is quite uniform. If copper is showing elsewhere other than a narrow band at the seam, replace them.

 

have you checked the e-shaft for runout

 

E-Shaft checked out fine... rear bearing was the worst and measured out of spec, so just going to go ahead and replace rotors and mains... you know what they say about an ounce of prevention...