Small End Con Rod Bushes

[moodyblue]

Have any of you ever replaced small end bearings in your wedge engines? What a pain! not as simple as press the old out and the new in. This is where I am at the moment with it unless someone has a better system.

[Hasbeen]

That brings back memories, not of little end bushes, but king pin bushes.

We had to ream every kingpin bush "back in the old days". We averaged 50 pairs of upright/stub axle assembles a day in my exchange components business in the mid 60s.

Do you have some sort of jig to ensure the bore is perfectly square. It doesn't matter much with a tractor, but if the thing is to rev a bit, it must be really square.

Of course that depends on the rod being straight & not twisted. I don't know how good our rods are, but I never found a rod for the old wet sleeve Vanguard/Fergy tractor/TR engine that was actually straight from the factory.

They weren't alone, about half the Cosworth rods needed straightening before use.

Hasbeen

[moodyblue]

Thanks for the reply Hasbeen, you've reminded me of the knocking from our old Fergy tractor that I used to hear as a kid. We've squared off the top of the vice and checked the rods for straightness. We'e also checked for squareness with a dial gauge clamped to the cutting head by running it up and down inside the big end. This should ensure that the small end will be reamed parallel to the big end. I'll probably go for a push fit with the gudgeon pin with a very slight resistance. It's one of those jobs that I didn't know whether to go for it or not, but with a new block I thought I should.

[john 215]

Hi,

Back in the dealership we had a jig that fitted in the big end and small end, that checked for twist and bend, got in the habit of checking even the new rods as once found one bent !

Make sure you get that oil aligned, seen that done before In most cases when these were reasonably new it was as cheap to put new rods in rather than re-bush them when you factor in time and labour costs.

Cheers John

[moodyblue]

Thanks John, I thought about getting new rods but wasn't sure if they would have bushes fitted and reamed.

[trsforever]

Hi, The proper method for doing little end bush's is honing, all good engine shops have a special machine for doing these, some time's they are machine bored first if there is a lot of material to be taken out but always final honed
as this gives a much finer finish (its not like a brake hone,its a very special machine) . Reaming can leave small high spots which flatten out after the engine has run for a while and then you have a rattlie little end, not what you need! Good luck.
Regards Scott.

[Hasbeen]

Use a little STP oil treatment in your assembly oil.

The way the STP rep sold us on using it for the first time was demonstrating how good it was at aiding fitting a tight gudgeon pin in a rod.

We were preparing the Hillman Imp engine for the Bathurst 500, & had it in bits. He asked for something that was a really tight fit. The gudgeon pin in the first Imps were so tight it was a chill the pin in ice, & warm the piston in the oven, & get them together quick. Otherwise it was a big press, or a big hammer job.

A little STP in some of our SAE 30, smeared on both, & the pin slid in with hand pressure. To say we were impressed is putting it mildly.

STP were offering a 2500 pound bonus for any competitor who won their class using SAE 10 oil with a can of STP in it for the race. That was about 2 years wage for a mechanic at that time, 1964, & we went for it. Half the field did.

No one had a problem, & the engine stripped beautifully. Impressed, I then used it in my Morgan +4, [TR3 A engine then]. It was so hard on it's big ends when revved over 5500 RPM it would have the slipper in the cap down to copper in 25 miles of racing. At Bathurst, where we were getting 6280 RPM down conrod, we had to change big end slippers between practice & racing.

With STP we could go 4 race meetings, including a Bathurst, & the slippers were unmarked.

Yes I know I sound like a salesman for STP, & todays oils probably don't need it like our old stuff did, but hey, as the old fly spray add said, when you're on a good thing, stick to it. Hell, I even have a 30% of a bottle in the S2000, & it shouldn't need it.

Hasbeen

[moodyblue]

Interesting stuff guys. I've found a parts supplier who has new old stock rods which have the bushes fitted, but they can't tell me if they're reamed. I sent off a gudgeon pin to them this morning and asked if they would see if it fits in the bushes, at least then I'll know for sure before I buy them. Anything else I should do if I buy the new rods? curious to see how the caps are marked for matching, as in our engines they are marked 1/1, 2/2 etc. I suppose they can go in any cylinder order, but not sure if they'll all be exactly the same weight. This could take a couple of weeks before they get back to me with the info I need regarding the bush reaming question. Thanks again for the advice.
Alasdair

[saabfast]

I suppose they can go in any cylinder order, but not sure if they'll all be exactly the same weight. Alasdair

Probably not all exactly the same weight from the factory but you can get them balanced along with the crank and flywheel by specialists. They do it as a complete unit. My son has had it done on the Stage 2.5 Viva engine he is rebuilding.

[moodyblue]

Thanks, I don't have the option of getting the thing balanced as I don't think anyone near me has the equipment to do it. I thought that if the rods were all the same weight, or matched appropriately, everything would still be in balance when fitted to the original crank, pulley and flywheel.

[Hasbeen]

I suppose anything is possible, & rods today may be made identical today, but I wouldn't be betting any money on it.

Back in my racing days neither Cosworth or Holbay forged rods, which cost about a months mechanics wage each did not come balanced, or even straight.

You can balance them yourself, if you like fiddly jobs. You have to support one end & weigh the other on a very fine scale. You can use a gudgeon pin across a couple of horizontal knife edges for the big end.

You will need a mandrill carefully machined to a neat fit in the big end to then weigh the little end. You need to get the whole rod, & each end to the same weight by the removal of metal. Note, don't grind the whole rod away.

It is a time consuming & fiddly job sure to give you a head ache the first time you do it, but is not rocket science.

We machined up a longer mandrill to replace the gudgeon pin, & measured the rod for straight by checking the mandrills for parallel, & by using a fully true lathe bed we could check the thing for twist, by sitting it on the mandrills.

Is this all worth doing? My F2 Brabham finished every race it started in the 20 months I raced it, & I believe it was this attention to detail certainly adds to reliability, & it won it's class in all but it's first race, beating many F1s in the process, so I believe it is no determent to power development either.

Hasbeen

PS. Google balancing a conrod, & you will find both high & low tech methods.

Hasbeen

[moodyblue]

Thanks for the advice Hasbeen, I see your point and the potential benefits for competition. Leyland couldn't get the Sprint to produce consistent power output, so as this is a road engine which probably won't get thrashed too much it should be fine. I'll do what I can to match the conrod weights but I'm happy that I've got the original crank, pulley and flywheel, even if its had a light skim these three components should still be within balance limits. I suppose we can only do the best we can with the tools and equipment at our disposal. I didn't balance my TR7 8 valve engine, I use it every day and I haven't lost a filling yet.