Assessing bearing damage (big end)

[EFA]

here is a picture of the #1 main and big end journals from my enginne following its short trip less oil pump last weekend.

 

I'm confused what to do.

 

The journals on 4-3-2 are fine, the shells from the big ends having picked up very slightly.

 

On cyl 1 there is slighht wear to the front side of the shell on the main, and the bearing is just starting to break up on the big end.

 

The only visible damage to the crank is some very slight scratches around the #1 big end journal. These are at most 0.001" deep, but non the less are present.

 

I'm looking for opinion on whether to replace the shells and fingers crossed or completely strip and rebuild the engine - if an intermediatry option is to polish the journal in situ, how can this be done?

 

Opinions please......

 

Fat Arn

Visit the K2 RUM website

See the Lotus Seven Club 4 Counties Area Website here

 

[Swiss_Tony]

Arnie

 

Sorry to hear about the engine trouble.

Its hard to tell from the picture.Going by the description of the journals I have seen worse and not had any wear or oil pressure problems.

If its any help I have got some Plastigauge. It may help to confirm the depth of the score marks. Also a good idea to check for ovality to be on the safe side.

 

James

Su77on Se7ens

Up to my neck in K-series and Duratec engines!

 

[F355GTS]

Arnie

 

if it's any consolation (I'll post a pic of my crank early next week and by comparison it's completely knackered) I'm sure yours just needs a polish but I've never heard of it being done in situ

 

Mark

 

Edited by - F355GTS on 10 May 2003 19:11:30

[sjwb]

Sorry to hear the news Arnie. Difficult to tell but if the dimensions are OK and the rods haven't pulled oval; build with new shells.

You certainly cannot polish in situ because of the danger of getting grit down the oilways. As the scratches are radial I wouldn't wory too much - taking into acount your depth assessment.

 

Steve B

[Bare]

Yes replace ALL the Bearing Shells (Mains and Rods).. they are easy and cheap.. Foolish not to:-)

General rule of thumb.. if you can't feel the damage with yer fingernail.. it's not worth machining to remove... Unless you are assembling a Compettition engine, in which case all tolereances should be exact.

Good luck.

 

[AMMO]

Arnie

 

The place to feel for damage is the underside of the big end journal. The opposite side from the visible part in the photo. This is usually the place where most damage would occur. If you cannot feel any wear just replace the shells.

 

To polish the journal in situ cut a strip of 1200 wet and dry the same width as the journal, long enough to wrap completely around the journal. Spray journal with WD40, wrap a boot lace a few times around the wet and dry and journal and pull the boot lace to and fro for a minute or so. Clean with contact cleaner or WD 40 and white kitchen towel. Be careful during the whole process not to let any WD40 / abrasive fall into the engine.

 

If you can see or feel scores after polishing the journal like this you then have to decide if you want to have the crank reground. If you can't decide this for yourself seek the advice of a competent engine builder. You just need someone who has seen a lot of cranks over the years for an opinion.

 

From what I can see of the journal it looks like it will go again. Woudn't mind seeing the uderside of the journal as well. Feel free to post more photos or email me direct.

 

AMMO

[oilyhands]

Second what Ammo says on the polishing, I've done it many times in-situ although with P2000 rather than 1200, just make sure you clean the crank oilways of any residual WD40 which may have carbide particles in suspension.

 

Look carefully on the thrust face for deposits of bearing material, if these are present be sure to polish them off.

 

Oily

[neilsjuke]

Hi Mr Webb sorry I think you should strip it if only to clean the metal thats now around the engines bits & bods ☹️

[Peter T]

Arnie, you would be foolish not to strip engine! This way you can accurately see any damage caused by lack of oil pressure. Just because the main bearings are easy to replace with the engine in situ, it does not mean that further damage has not been caused , best check every bearing in the engine, from small end to camshaft. If you were to 'Hope' that the only damage was visable via a non engine stripdown, then it is possible that further bearings having allready sustained oil loss, could without warning completely disintigrate, causing mass engine failure!

 

On The Starting Blocks!

[Swiss Tony]

If you replace the bearings make sure you get the right sort.As all reputable VX experts know there are two types available. You want Lead Indium type not Reticular Tin in a high revving engine. Pretty sure that QED & SBD sell these. Swindon certainly do.

 

Reticular Tin aren't up to the job.