Oh B*****r - thoughts please

[mep12345]

I'm pretty sure I know what I need to do but just want to canvas opinion before I do it. I re-assembled the lower half of the engine this week and guess what - I forgot to "mis-align" the piston ring gaps. So I set about removing the pistons and set the alignment before re-installing - luckily all went well the job was very easy and done in less than an hour. However in doing this I noticed one of my new big end bearing caps was scored; had I not made the earlier error I would never have found this. I investigated the scoring and found that the crank journal for piston 4 had a small dink in it with a burr, the burr causing the scoring of the bearing face.

Thinking back I think I know how I did this (basically caught the conrod on the journal face when intsalling the piston) and am really p*****d off clearly, but sometimes things happen. Anyhow, I have dressed off the burr with a stone and now have a very small indent on the crank journal that is just visible and just able to be felt by hand (about 0.75mm diameter and probably much less than <0.1mm deep). The crank journal still measures as round as it was basically the burr I removed and not journal material although the "colour" from the journal material was removed in the proximity of the dent. The dent no longer marks the bearing face on hand rotation of the engine. I believe my options are:

1. Stick with current dressed crank and change bearing again for this piston only using one bearing from a new bearing set or one of the old bearings (all were in excellent condition when removed and only changed because the engine was stripped). - minimal work and expense

2. Remove crank and replace with my spare (higher mileage but still within original tolerance and in excellent condition) and replace damaged bearing as above with either new or one of the old ones. - a few hours work and minimal expense

3. Remove the crank and have re-ground using an underside set of big end bearings max work and expense but closest to returning to new spec.

I think I need to follow option 2 with new bearings but would really like to not have to disassemble the engine again if it can be avoided so your thoughts sought just so I know I have made the correct decision.

Cheers

Mark

Oh by the way - does this get me the dunces cap for this week?

[jwoffshore]

I think you will be fine with option 1 if the bruise is as small as you say (0.75mm).

That bruising is usually caused by the sharp threads on the end of the con rod bolts after you have taken the cap off. As a precaution, once the cap is off but before starting to push the piston/rod out, wrap some tape around the end of the bolts or slip some rubber tube over them. Leave the tape or tube in place when re-installing the piston/rod until you have the rod sitting properly on the crank.

I've learned that by making the same mistake as you!

[phillpot]

jwoffshore said:

I think you will be fine with option 1 if the bruise is as small as you say (0.75mm).

+1

maybe even re-use bearing shell (after clean up) on another journal



if the hat fits.....