Last build on my 355 was a shade loose and I couldn't carry very good oil pressure at 6800 even with 20w-50. So now that Im back apart I was thinking of closing up a little by using 1 half of a +1 set on the rods and mains. I've heard of this before. Any opinions? Which side should I put the oversize in or doesn't it make a rats butt.

Thanks
Steve

 

Steve,

Yeah you can do that it doesn't matter which side goes where but I usually put the tight side on the top.

At least get some NEW plastiguage if you don't have a bore guage so you know what the main clearances are.

Bret

 

Thanks,

I'm gonna dial bore gage them this time to make sure. I'm not real comfortable with plastigage.

Steve

 

That's a good idea. Make sure you check the crank with the same mics you set the bore gauge with and you can get the exact clearance.

Bret

 

Yep, good idea. I know how easy it is to get mics off a couple of tenth. Usually happens when someone uses them as a C-clamp

Steve

 

make sure you know how to use the dialbore and mic properly, poorly used tools like this are worse than plastigauge!

 

Steve,
what clearance are you currently running on the mains and rods? It is certainly not recommended to run offset bearing sizes. Obviously you will have a short oil wedge on one side, not to mention vertical eccentricity. Would you buy a crank .0005 OOR?


You would be much farther ahead polishing the crank and running a +2. Remember that the stock oiling system is designed for a total wedge of .0011 . If you have more clearance then this, I would recommend looking at the oiling system. I feel that the factory tolerance is far to tight for an application like yours.

Good Luck
Dennis

 

Every real engine I have ever seen has had mixed bearings like SStrokerace suggested and that includes NASCAR 75G Cup engines and Pro Stock engines. It's done everyday in almost every real race shop in the USA.

 

Thank you Erik, at least we can agree on something!

Dennis,

Can I ask what your experience is with grinding? Grinding .0005 off of a crankshaft evenly where the crank is not oval shaped on the main or rod journals is hard.

And I'd love to know who sells +2 bearings?

Bret

 

Bret,
I don't remeber saying anything about "grinding .005 off?"


I indicated that the oil wedge would be ecentric by half a thou....

I also indicated that I felt he would be better to go smaller on the pin, and run a larger bearing set (+2 being worse case scenario). Normally roll polishing takes a couple tenths off. This should get him into atleast a full +1 set. But no one is talking clearances so it is all speculation at this point. In a low RPM application, I believe you can go as tight as .0018 on the rods and .0022 on the mains...but keep the oil wedge constant.

bret,
Both clevite and FM offer +2's in their lower performance lines of bearings. You can also get clearance sets from fm performance if you get the right guy in sales. they are nothing more than overplate blems.

Erik,
I have seen this operation of cluster fornication before also. That certainly does not make it correct. Its basic physics man... round pin, round bearing.

I am not sure where you were going with the "real" stuff...maybe the fictional engines that I work on require more care the this "real" stuff you work on.

whose cup and pro stuff are you working on? Some of the worst workmanship I have seen has been in cup motors. Although of the big 5 doing pro work that I know of, I would certainly hope none are playing these games.

Have you had a chance to play with the -3 heads yet?

Good Luck
Dennis

 

Dennis,

If you are that **** about bearing clearances and would rather use the lower end of the scale on bearings and trade off bearing embedibility for a +.002 size I don't know where your priorities are.

My point of grinding .0005 off (not .005 big difference there) is how else are you going to get a bearing clearance in spec when the spread is .0020-.0025 for example. If it's at .0027 or .0017 you have to add or subtract a .0005 to get it in spec.

BTW Polishing is for surface finish and to have the grain lay over in the direction of rotation, not to remove stock. Then again what do I know about grinding, our family has just done it for 40 years.

Bret

 

Thanks
Dennis

 

FWIW, If I recall my bearing clearances were between .0025" and .0030" as measured with plastigage on a new Eagle forged crank and H beam rods and King Acular (sp) bearings. My eyeballs could not really distinguish anything in-between that with the plastigage method. I was running a stock pump and pan. Even with marginal pressure and a season worth of 6800RPM passes, the crank journals look perfect. I will certainly dial bore the bearing bores and mic the crank to get more accurate numbers on this winters refresh job. I plan on running a HV pump and Canton pan this coming year. If I'm correct, all bearings have some eccentricity built in. Yes?

Thanks for all of your responses.

Steve

 

Well I really don't know about all that Dennis! ALL professional engine shops I have ever seen in drag and endurance do this (although most drag racers don't even measure bearing clearance). Bearings are not round in the first place either. Not even close! They have much more clearance horizontally than vertically on even medium eccentric bearings like the H series. There are even rod bearings where the tops and bottoms are asymmetrical on purpose.