Big End Bearings Urgent Help Needed!

[m5nut 0]

I have a 1.9 that's developed a slight knock (almost inaudible over the engine) from the bottom end. I know the sound all too well as my previous engine seized due to this

 

My question is: What size/undersize shells do I go for without the need to regrind the crank? I need the car on the road asap and can't afford to waste time having the crank out etc.

 

Gonna be running some silkolene silkolube 20w-50 to aid oil pressure and act as a thicker buffer, plus will be fitting a grp A oil pump spring.

Should this fix the knock or am I being hopeful it doesn't need a rebuild?

 

Whatever happens I need the car very soon, as riding the bike to work is getting very cold and slippy.

 

Thanks in advance

Bob

[Miles 331 1 Cars]

you will need to take the crank out, Sticking in new bearing's is false economy as even if the crank looks OK without measuring it you don;t know, Also depending on how bad the knock is you may need a new Con rod too

[Tom Fenton 1,541]

Yep absolutely right. A guy I know did the same thing, replaced the big end shells without having the crank out. It had spun a shell in the rod and ran for about 30secs on the new bearings before it started knocking again. I rebuilt it for him, full strip, crank grind, it had knocked just over 12 thou out of the big end journal and the rod also needed to be resized. The normal oversize shells are +0.3mm, running it again had knocked 0.35mm out of the journal, luckily we managed to get a set of +0.5mm big end shells to be able to reclaim the crank, as otherwise it would have been scrap.

 

So basically if its knocking it needs the crank out to sort it.

[m5nut 0]

Miles thanks for the bad news

I was almost gonna buy a set of shells off your eBay store. Tom thanks for the details, but I have a question;

 

If the crank is worn by 12 thou, does that journal need to be ground back 12 thou all over to make it circular? Basically do they wear oval? If so, a reground journal is now 12 thou undersize and the rod is .35mm over. So what size shell would this example need? ie. .35mm + 12thou = what? :edit: found out it's .65mm, so in the case of the engine you rebuilt Tom, wouldn't there still be .15mm play in the bearing or is that close to the specified tolerance??

 

Oh well time to get a winter run-around and store this bloody moneypit till the better weather comes and i've the money to do it

 

Thanks for the help guys

Edited December 7, 2008 by m5nut

[nick 3]

If this is just an 8v, it would be far cheaper and less time consuming to just bung a decent s/h engine in. You should get a known good one for less than a ton and then just spend a day fitting it. You can then rebuild the old lump at your leisure.

 

Nick

[Tom Fenton 1,541]

I think you've misunderstood my example. A standard crank uses standard size bearings. When the guy changed them he just put standard size replacement shells back in, but this was no good as the crank journal had been knocked undersize by the bearing failure, and the rod bore was oversize from the bearing spinning in the rod bore.

 

So first off the rod was resized back to its standard size, so the cap and rod have a small amount of material removed from the mating faces, and then the cap and rod are bolted up firm and the hole (which is now oval) is machined back to round, the correct standard size.

 

Next onto the crank. The common oversized (smaller hole in them) bearing shells are 0.3mm. However the crank on this engine even though it hadn't been touched before had worn due to the knocking and shells spinning so that it had worn more than 0.3mm. Therefore I got some 0.5mm oversized shells, and had the crank journals ground to suit these bearings and give the correct running clearance when they are installed.

[Miles 331 1 Cars]

All dome and gloom but the cranks can also bend when this happen's, I;ve found more often than not small knocks do the most damage and big knocks can be got away with

[m5nut 0]

Thanks Tom for the clarification, I now understand completely. Will any precision engineer be able to the machining of rod and crank? Or is it best to take them to an engine builder? Hiflow Heads is 5 miles away so I guess taking it to Andy is the logical thing.

 

Nick....not wanting to go through the hassle of doing anything to it right now. It's too cold, too dark and I'm too sick of working on it. I'll wait to Spring when I'm not so desperate to get off my motorbike and into something with a heater and a roof. Plus it's still to be mot'd and taxed before it goes anywhere

All dome and gloom but the cranks can also bend when this happen's, I;ve found more often than not small knocks do the most damage and big knocks can be got away with

Oh for fcuk sake it never rains but it pours doesn't it? Thanks for that Miles, I'll get it checked closer to the time of rebuild.

 

But for now I'm looking for something with a years ticket that's sub £500 and close by.

 

Thanks again guys

Bob