Model 20 Twin Bigend - oil problem

johnnyb · Post by **johnnyb** » Sun Jun 13, 2010 1:31 pm

Hi guys,

I have been chasing a problem where after warn up (5 min) I lose all oil flow to the rockers. I have changed the oil pump, removed metering plugs etc etc (detailed in a previous post).

While I had the barrels off I checked the movement in the big end. There doesn't seem to have any up and down play (i have 50 w monograde oil in the bike which could be taking up the slack) however there seemed to be a lot of movement if I rock the conrod from side to side.

I have convinced myself my oiling problem is caused by big went wear, where the engine heats up and the big ends expands causing oil pressure to drop due to excess play.

Any advice on bigend play or oiling issues after warn up? Its going to be a big job to do the big ends...just wanted to ask before I went too far.

cheers
john

paul knapp · Post by **paul knapp** » Sun Jun 13, 2010 1:46 pm

Have you checked the oil pressure with a gauge?

Eric · Post by **Eric** » Sun Jun 13, 2010 2:45 pm

You do need to check the oil pressure, but is there any audible indication of big end wear?

Mine would develop a knock when accelerating and pulling before going quite as you eased the throttle. But many section members who tried it at the time said it was OK.

When stripped it needed to go through two re-grind sizes because the crank had worn oval the bearing shells were down to the copper backing.

What I am trying to indicate is that the slightest hint of a noise probably means the big ends are almost certainly worn. Trouble is other things can also make a similar noise.Edited by - Eric on 13 Jun 2010 1:49:02 PM

Groily · Post by **Groily** » Sun Jun 13, 2010 6:36 pm

To add to Eric's thoughts - when I was in a similar situation to his (but only one regrind size needed!) there was no loss of top end oil feed. I'd be surprised if slight wear in the ends would cut off the supply completely. Like Eric's, mine were lightly audible.
Was it running fine for ages and miles and miles and this suddenly happened, or is this something that's happened since it's been played with? I'm thinking of all the changes in the oil system over the years, the filter etc, the state of the oil distributor bush, etc etc, the oilways to the top end, the rocker pillars and shafts, the whole lot. Are the cylinders and cases correct for the year ('53?), with annular grooves on the upper part of the lower spigots on the barrels and plain throats in the crankcases? (This was reversed on later ones.) There are a few nasty reasons why the oil system might have become deranged, especially if someone unfamiliar with the differences has been at it. (Don't ask me how I know - I was once far too unfamiliar . . . .)

laxy · Post by **laxy** » Sun Jun 13, 2010 9:58 pm

Johnny, how do you know oil is getting to the rockers during the first five minutes then stopping? have you run the engine from cold with the rocker covers removed?
If as you say youve checked oilways are unblocked etc then perhaps the oil distrbuter is suspect.They changed design slightly over the years.You may have the wrong one or the right one in poor condition.With the end cap removed can you see it turning as the engine revolves using the k/start

Don Madden · Post by **Don Madden** » Mon Jun 14, 2010 12:37 am

The oil restricter started with just a brass jet & later changed to the rotating distributer with a hole in the side to index with the oil passage. The hole size was increased at least once, & in 1956 was replaced with a flat. The 1953 should have an early distributor with the small hole, which may be blocked. I suggest you clear it out. Be careful about just replacing it with the later type as they also experamented with oil jets in the cases or heads to control flow. Seemingly, the flat type, while less prone to clogging, passed too much oil to the heads without restrictors. Cheers, Don.

johnnyb · Post by **johnnyb** » Mon Jun 14, 2010 1:24 pm

quote:
Have you checked the oil pressure with a gauge?

Hello Paul,

I haven't check the oil pressure with a gauge to see if the pressue is dropping off dramatically after warn up. It will be a good idea before splitting the cases.

regards

johnnyb · Post by **johnnyb** » Mon Jun 14, 2010 1:34 pm

quote:
You do need to check the oil pressure, but is there any audible indication of big end wear?

Mine would develop a knock when accelerating and pulling before going quite as you eased the throttle. But many section members who tried it at the time said it was OK.

When stripped it needed to go through two re-grind sizes because the crank had worn oval the bearing shells were down to the copper backing.

What I am trying to indicate is that the slightest hint of a noise probably means the big ends are almost certainly worn. Trouble is other things can also make a similar noise.Edited by - Eric on 13 Jun 2010 1:49:02 PM

Hello Eric...no audible noise from the big ends. I'm very surprised with the conrob rocking movement that there isn't any noise however some people don't seen to worry to much about this movement....I'm more used to working on dirt bikes and Ducati's from the 80's where this movement is minimal if non existent.

johnnyb · Post by **johnnyb** » Mon Jun 14, 2010 1:45 pm

quote:
To add to Eric's thoughts - when I was in a similar situation to his (but only one regrind size needed!) there was no loss of top end oil feed. I'd be surprised if slight wear in the ends would cut off the supply completely. Like Eric's, mine were lightly audible.
Was it running fine for ages and miles and miles and this suddenly happened, or is this something that's happened since it's been played with? I'm thinking of all the changes in the oil system over the years, the filter etc, the state of the oil distributor bush, etc etc, the oilways to the top end, the rocker pillars and shafts, the whole lot. Are the cylinders and cases correct for the year ('53?), with annular grooves on the upper part of the lower spigots on the barrels and plain throats in the crankcases? (This was reversed on later ones.) There are a few nasty reasons why the oil system might have become deranged, especially if someone unfamiliar with the differences has been at it. (Don't ask me how I know - I was once far too unfamiliar . . . .)

Hello Groily,

The bike has been running fine for some time until I noticed excess tappet noise. I check and found a rocker very worn on the shaft due to lack of oil. This is how I discovered this oiling issue.

The only reason I suspect the bigends is I running out of ideas however you guys are giving me great information which I can use to try and solve this issue.

The heads and cases are a match however I will have to confirm the rest.

johnnyb · Post by **johnnyb** » Mon Jun 14, 2010 1:51 pm

quote:
Johnny, how do you know oil is getting to the rockers during the first five minutes then stopping? have you run the engine from cold with the rocker covers removed?
If as you say youve checked oilways are unblocked etc then perhaps the oil distrbuter is suspect.They changed design slightly over the years.You may have the wrong one or the right one in poor condition.With the end cap removed can you see it turning as the engine revolves using the k/start

Hello,

I have been running the engine (stationary..not riding) without the rocker covers. When I first start the engine from cold oil gets to the rockers (takes a minute to get there) however after about 5 minutes of running the oil stops getting to the rockers.

I have checked the oil ways several time and even removed the metering plugs.

I think the next move will be to chenge the oil distributor with a later version (with cutout).