Hi I've got my motor completely disassembled and ready to put it back together. I noticed that the worn big end bushes that are currently on the rod have holes in them, assumably to allow for oil flow from the holes in the crank. I've got two new ones that don't have a hole in them at all? Do I have the wrong part? They fit snug, they just don't have any holes?
Well you do not have the factory shells but in my opinion you have the right ones, the bottom shell should be plain anyway, the top one should have one hole but you can fit a plain one here too. To make sure you do not reduce the oil going up to the piston you can file a wide but vertical shallow groove on the side of the con rod alongside the top shell, this should be 1mm deep and 5 or 6mm wide, as the oil exits the shells this groove will direct the oil upwards. Radius the corners of the groove generously with no sharp edges.
This pic shows an example in a car rod, its the round bottom groove part way over but you do yours central. You can see the generous rounding and the groove does not even go near the shell as its within the chamfer on the OD of the big end.
Just be sure your rings can handle the extra volume! Triumph tried this on their twin and had to send the dealers a peen with which we had to close the hole. Rather than tearing the engine down they had us do it by removing only the cylinder.
For the most part people have abandoned the random approach for directly spraying oil at the underneath portion of the piston.
I think most aftermarket bearings come un drilled due to differences in crank shaft drilling, and they leave it up to us to locate the correct spot to drill. I would absolutely drill them, and chamfer both sides of the new hole. The crank side more so than the rod side.
For the oil spray reliefs... I assumed these were to send more oil for the wrist pin/small end bush that for the underside of the piston. I imagine this has to be planned, and executed carefully to direct the oil onto the correct area. I can easily understand (as mr. Healy pointed out) willy-nilly spraying oil around in the crankcase could lead to problems. Especially for the fellas using Dino Oil.
Perhaps an old crank, and rod set up, and some experimenting to get the correct placement of these "slots" is in order. One rod, some fast set epoxy, a dremel tool, and a pressure feed system should sort that out quickly...
I like modifying everything I can, and oiling systems generally respond very well to well planned improvements. Well planned is the key.
The best setup on the B25 is the last incarnation of the T100 con rod, this has no holes which are a weak point in a B25. Once you eliminate the hole you then have the decision about if the oil from the hole was needed or not, thats where the con-rod groove comes in.
Here is the result of the hole being a fatigue propagation point. I would be risking a decision on the groove before adding the hole, worn rings over con-rod sticking out of cases wins every time
Re: Big End Bush 1968 TR25W Hole or No Hole?
#609304 07/19/158:20 pm07/19/158:20 pm
The last year for the 250s, 1971 got the oiling right. But the rod still used the oil hole in the top. The triumph 500 also used the hole hole in the top. But oddly enough only on one rod. The later rods can be quickly identified by the peaks on each side of the upper half when looking at it from the side. The earlier ones are still round in this area. You can use the later rods on the earlier cranks, you will have to clearance them to the flywheels. For my normal riding, the stock set up works fine. If I was riding like I was 45 years ago, then I would get a hold of Ed V. and have him build a crank with a Carrillo rod. Jeff
I did not know that you could get a T25 rod with out the oil hole. I have a couple of NOS ones and many used ones(all 1971)and they all have the hole drilled in them. I also have several 1973 Cranks/rods and a few NOS rods. The T100 had a oil hole on the Drive Side connecting rod, but not the Timing Side. Jeff
Thanks for the advice. I didn't want to risk some primitive grinding on my part and ruining a good rod. I am not happy with the play in the rod on the crank once I tighened it up. Once tight, the rod barely moved on the crank! I am going to order a new set of big end bushes and will drill them out to replicate the old.
Old school, buy Plastigage. Lay it on the bearing , tighten, remove, use the gauge on the paper it came in to measure. This will tell you how much clearance that you actually have. Tighten up, place a old pumper oil can on the end feed hole of the crank and pump oil in until it flows out around the rod. Rod should drop down by it's own weight. Jeff
250 models had a major flaw in the crankshaft/flywheel design. It had a major effect on oil pressure and life of the connecting rod bearing.
The sludge tube was located in the timing side flywheel. The flow of oil into the sludge tube spanned the gap between the crankshaft o.d. and the flywheel i.d.. The machining was so poor that oil destined for the rod bearing would spray out from between the two.
While they never did address the cause they did finally remove the oil hole from the rod and the bearing shell. It wasn't enough, but all that could be expected from a company that was broke.
The problem wasn't unknown to the dealers and people who raced 250's and they plugged up the sludge tube and installed an external filter. The big end finally got enough oil to survive. This is a service Ed at E&V, and others continue to provide to people who want a reliable 250.
Follow the factories lead, don't drill the bearing shell!
The T100 had a oil hole on the Drive Side connecting rod, but not the Timing Side.
If you are interested in Triumph 250 models please take the time to read this Service Bulletin. Triumph distributors had already realized the problem with the oil pressure (which BSA (they built the engines) never did anything to cure) with the 250 as early as October 1968. Read between the lines as Service Bulletins often understate a problem. The 250 quickly garnered the nickname "Twud" by dealers who saw plenty of 250 connecting rods. Some of the more clever dealers were plugging the sludge tube and fitting 500 rods and bearing shells as BSA was running out of replacement rods. You see from the bulletin the factory choose using some sealant to solve the problem
Yes, K but we are talking about the engines. I had a salesman who loved selling 250's. His biggest year, if I remember, was 1969 where he sold 50 of the things. He was a sadistic young Polish lad who actually had the guts pa to sell one to Edsel Ford. Edsel was going to school at Babson College near our shop. I think his real motivation was to irritate me, but he sold his share of twins and triples.
While BSA spent a lot of money "tarting" up the visuals. An old version of spending time at the gym, while they should have been spending more time at the cardiac surgeon's office. They should have spent more time at the heart of the problem... rod and sludge tube. The problem was discovered, and cured, by the service team at TriCor in Baltimore two years before the 1971 was introduced. Dealers like ourselves were getting rods without holes, blocking the sludge tube and fitting an external oil filter while BSA turned a deaf ear...
Why would you drill an oil hole in the most critical portion of the bearing where the hydrodynamic wedge is formed. We go out of our way to get bearing clearances right. Use the right grade of oil so that at ambient operating temperatures the oil viscosity is within the range that will allow the wedge to form. Make sure the crank journal is round and straight to insure the wedge will form. Only to drill a hole at the most critical point. Oh, we will put in a bigger pump to compensate for the oil spraying out the flywheel and out the hole in the rod... Great!
And why? I am told to lubricate the drive side roller bearing. A bearing that will run in a mist of oil, and there is plenty of that in one of these engines. So what was the idea here? To make a 100,000 mile roller bearing for a connecting rod and rod bearing that, at Interstate speeds, is good for a few thousand miles?
Well at least in 1971 they did fit an external oil filter so part of the job was done for you...
I would be amiss if I didn't give BSA credit for a much better combustion chamber than Triumph. If this engine had a classic Triumph hemi-combustion, and the resultant increase chances of detonation, you would have seen a lot more of split rods. John
I was hinting at the workers on the line taking a dim view of the badge on the tank and the primary cover and installing a few added gremlins. These were over and above the inherent design flaws and provided free .
The 1969 TR25W factory manual is the best factory one to work off on this bikes especially when used with the Tri-cor engine assembly tip sheet, lots of added fix's and care points over the BSA version.
Re: Big End Bush 1968 TR25W Hole or No Hole?
#609489 07/21/1510:03 am07/21/1510:03 am
Now be nice... I wouldn't have wanted, for all the money and prestige at hand, being Edsel. Edsel wanted nothing more than the rest of us wanted. To enjoy the freedom and friendships one has in the two wheel community.
Lindsay Brooke recently interviewed Edsel at Charlotte Motor Speedway. He fondly remembers the bike, now remembered just as a Trophy. He did wander into a bit about dad, and how he wouldn't have approved of the adventure on two wheels. Mind, he only used it to run around campus, and I suspect for that occasional mile jaunt over to Wellesley College. Babson College was founded to serve, and groom, the sons of the industrial class. Wellesley is an all women campus and they to have groomed many of the women women leaders in the country - Hilliary, for example, is a graduate of Wellesley College.