big end bearing question,

[artyb]

hi guys,
a question for you mechanicaly minded folks,

i have built a few engines,
and a friend f mine has a vw 1600 flat4 engine that was rebuilt 500ish miles ago,

it sounds as if one of the main bearings, is worn a heavy knock on exceleration
if it it is possible, any idea what would cause it
and if we strip it down could we get away with new shells,
the engine had a new crank pistons and barrel, not sure about con rods,

 

[calumscott]

If you have such a knock then get it checked as soon as possible. Each knock is doing more damage to whatever it is.

If you put in a spanky new crank surely you would have put in new bearings at the same time?

If you didn't - you are in the position where you have a perfectly smooth surface on the new crank, but a ridged and pitted surface on the bearing shell. Those will busilly wear themselves to fit...

...or really not fit.

And if there is any slack in there - you get knock. And if you get knock it's going to hammer the remainder of those shells into some weird shapes - usually out the side of the big end and that's not a good place to be.

I'd get new shells in ASAP and see where you go from there.

 

[artyb]

nice one callum... :thumb:

i would imagine the guy who done it should have done the shells as there only 9 quid...
but who knows...?
im sure it wont become evident until we have bits all over the workshop... :lol:

 

[TRXnMe]

Best to strip the engine, a nice easy job on a VeeDub flat four.

Get the crank out, mic it up against the spec (check it at as many points around 360 degrees as you can), if it's in spec replace the bearings and rebuild the motor.

While it's out it's worth checking the main bearings in the crank case as well.

Lovely simple motor to work on, and one of the easisest to get out of the car :)

Once rebuilt make sure the oil pump is working and developing pressure, it would be annoying to find the new bearings knackered in another 500 miles.

 

[artyb]

great inspiration there.. thanx
how do we check the oil pumps working... :hmm:

 

[TRXnMe]

great inspiration there.. thanx
how do we check the oil pumps working... :hmm:

With the crankcase built up, and filled with oil, turn the crank over several times you should get oil out of the oilways up the head to the valve rockers, if you don't then it might be knackered, either too much play around the gears or the drive might have broken.

If if it's still built I think there are a couple of external oil ways on the VeeDub motor, you can use these as a pressure take off point, fit a guage to that, you should be able to get a cheap one off eBay, and see what the oil pressur eis when you start it up. Don't expect the guage to show the required pressure, you will be losinng some due to the knackered bearings, but you should still be close.

 

[TRXnMe]

The oil pressure gauge in the link isn't cheap, but it does use the current pressure switch as pick up so easy to fit.

http://www.bus-boys.com/bbvdo.htm#pressure

This one is cheaper, but not specific to the Bug, so worth giving the seller a bell to see if the adaptors will fit :)

http://www.ebay.co.uk/itm/Tim-Oil-Press ... 3f11891d95

 

[screamlead]

Just my 10p worth i used to rebuild beetles and always heard somewhere there were always probs with oil circulation and something to do with small holes in the case getting blocked with gunk over time.
Never actually took an engine apart but removed a few so agree thats the easy bit.
Think the oil filter is the naff bit too. Good luck anyway.

 

[artyb]

had a listen to this engine today,
and the knock is barely audible...
i spoke to the guy who rebuilt it,a keen amateur mechanic,
he rebuilt it as a valve hit a piston,

the heads were replaced,with decent second hand ones,
he used;
brand new..
crank,
barrels,
pistons
oil pump,
shells,and other external parts,
reused the conrods,

it ran really well for 500miles

he reckons a shell has gone/slipped

 

[Bru4u]

When you strip it, rod out and then blow out all the oilways, it really sounds like oil starvation, you can get small rods and brushes for this. One of my subscriptions on utube is this a bit geekish but for an engineer and machinist, pure porn

 

[artyb]

:thumb:

im tending to think an oil way is blocked,

 

[TRXnMe]

Do still check the crank for tolerance and make sure it is still round.

It is almost certainly a big end shell, or plain bearing, that has gone, so that is probably loss of oil pressure, probably caused by a blocked oilway, enjoy shoving pipe cleaners into small holes for a while :)

 

[artyb]

for those that know these engines..
there is no play on the pully ie no end float,

 

[TRXnMe]

That's Good :)

If this is explaining the obvious, I apologise, but a couple of your posts seem to inndicate you might not know much about the inside of an engine, so here we go mechanics 101 :)

The crank is the bit that is connected to the pistons, and the clutch. The pistons force the crank to turn, as it turns it delivers power through the clutch to the gear box.

In order for the crank to spin it is mounted in bearings, usually plain bearings (a sheet of metal, rather than ball bearings) as they can take greater pressures.

There are two sets of bearings involved with the crank, the main bearings are mounted in the crank case, if you'd got end float it might indicated wear on these. The main bearings allow the crank to rotate in the crank case.

The other set of bearings involved in the crank's rotation are the big end bearings. These are at the point the con rod meets the crankshaft, they allow the crank to rotate as the conrod moved up and down in the cylinder bore (generating power), they are also most often plain bearings.

The bearing at the point the conrod and crank meet is called the big end bearing, it's this one that is most likely to be making the knocking noise, the oil is usually supplied to these bearings through small tunnels in the crank itself, if these get blocked (as has been suggested) you're in trouble, but they can be cleaned,you will need to remove the crank though.

 

[TRXnMe]

I'll see if I can google up some images to show what I'm talking about if you want?

 

[artyb]

thb
ive built a couple of 2.1 pinto engines for kit cars,
and a couple of v8s too,
so ive seen all the components... :whistle:

but never seen a bug engine close up b4

im gonna get to know one intimately soon though,

 

[TRXnMe]

It's no different to the pinto really, just 'flatter'

I like them, not had to work on one for years though as motorbikes are my passion and I can't have two 'toys' at the same time due to lack of space and funds :)

 

[artyb]

fair play ... :thumb:
i have a gsf 1200 bandit in the garage ... :party:

 

[artyb]

heres a free table i knocked up a couple of years ago,
with bits of pinto engines i had left over that were scrap..

the flywheel,crank and pistons topped of with a piece of welsh slate

 

[TRXnMe]

Nice table, ever thought of offering to flog it to Top Gear?

There's an Aprilia Falco in my shed, it's in bits but on the way back together after minor 'heart surgery' to the beast, cash permitting it will be out and about in June.