Mk 2 Big End End Float

[allan.walker]

The change from white-metalled rods to shell bearings took place for the 1948 season so no, the dates don't tie up.

Thanks Paul. That makes me wonder if the reduction in the width of the journals in 1951 was a deliberate decision to limit the clearance of the rods to less than the original spec. If this were the case, John, using a crankshaft with greater than 5-12 thou is probably not the best idea.

[John.reader]

Thank you for all your replies, and thank you to Alan for maybe confirming my diagnosis of the mysterious knock in my first engine. I still have this engine, and I have included a short video at the end of this post showing what it was like.

Alan, really pleased for you as you have hopefully sorted out your problem, but no such luck here at least so far.

Whats really puzzling me about this is that in total I have six rear crankshafts, the four that I mentioned in the first post plus another two that I didn’t mention as I already knew that the were unusable. One is in the bottom end of a wrecked engine, and it has the wide bearings anyway. The other one rather annoyingly has the narrow bearing journals, but it also has the splines on the cush drive end worn half way through, and even worse it has been laying in water at some time and the thread on the drive end is heavily rusted away. I have tried cleaning it up with a wire brush, but there is so little of the thread left that a new nut just wobbles on it and and if it was done up tight I know that it would strip the thread in the nut. Shame.

However, all these crankshafts must have come out of running engines, and the two that are on standard size have never been been near a crankshaft grinder, so they must have all been running in their previous lives for many years with the wider 30thou clearance. Surely these engines didn’t knock like mine did otherwise Ariels would have gone out of business, so maybe the end float is not the the cause of the knock, but if it isn’t then I’ve no idea what was causing it.

Anyway, in the absence of a usable shaft with the narrower big end journals, I suppose I’ll just have to get the best one of the wider ones that I have reground and hope for the best. It must have been OK in its previous life, so maybe it will be OK again.

I don’t see what else I can do really.

Anyway, thank you all again for your help.

[allan.walker]

One other possibility to solve your problem, John. Bennet Longman (Iron Horse Spares) has just had delivery of a batch of new con rods. Some of these have been made with 20 thou wider big ends, in order to address the end-float issue. The only snag is that they cost £645 per set.

[John.reader]

Hi Allan, and thank you for the information. I knew that the club were getting some more rods made but I had no idea that they might be imminent. I will certainly follow it up.
Just an idle thought, if the new rods are wider, it might mean that I could reuse the freshly reground cranks from my original engine, which would save a few bob to put towards the cost of buying the new rods, although some careful measuring would be needed first. Its a possibility though.
Many thanks again for your help.

[allan.walker]

Just an idle thought, if the new rods are wider, it might mean that I could reuse the freshly reground cranks from my original engine, which would save a few bob to put towards the cost of buying the new rods, although some careful measuring would be needed first.

If you have 30 thou play now on your reground crank, the wider rods should bring this down to 10 thou. Not exactly snug, but within stated tolerances.

I think it's also worth mentioning that Bennet may sell you two wider and two standard rods, if you have just one crank with excess clearance.

If you're wanting some rods, it's probably a good idea to contact Bennet soon. Initially, he was asking for a commitment to buy before the order for new rods was placed. Doubtless he ordered some more over and above, but how many will be for free sale, I don't know.
He did specifically tell me that there wouldn't be that many wider ones made.

[John.reader]

Hi Allan, and thank you for the information about the rods, without it I wouldn't have known that they were available.

Anyway following your advice I have contacted Bennet, and he has agreed to supply me with a full set of the wider rods, so hopefully this will solve my problem.

I'll try them on the reground crankshafts from the original engine first, but if the clearance is still too wide then I do have another front crank with the wider bearings, and I'll have to get that reground along with the best of the rear cranks that I have.

Again thank you for your help, and I'll let you know on here how I get on. Thanks again.

[Knud.Degnbol]

Perhaps a stupid question. The wider conrods. Do they come with wider bearing shells?

[david.anderson]

While the oiling of the crank and resultant oil pressure may be affected by the end float of the conrod, most Mk2 builds involve the fitting of a Morgo oil pump. The Morgo pumps to a higher pressure and has a much greater flow. Much of the extra flow ends up draining from the timing cover into the crankcase after it is dumped there by the pressure relief valve. So possibly some extra clearance on the conrod to journal may be beneficial in that more oil will escape within the crankcase giving extra oiling to the cam and cylinders. Just a thought.
David

[allan.walker]

Perhaps a stupid question. The wider conrods. Do they come with wider bearing shells?

Not a stupid question at all, Knud.
The shells are the same width. Shells are usually narrower than the conrods to allow for the shells to only bear upon the flat area of the crankshaft and not make contact with the radiused edges to the crank webs.

[John.reader]

Four of these beauties arrived yesterday, they are the new club rods, and these are the +20 thou across the big end version.

Altogether a beautifully made and impressive piece of kit. Shame they end up hidden inside the engine.

Hopefully these will enable me to overcome the excessive end float that comes with using the standard rods on the earlier wider bearing cranks.

Many thanks to Bennet for sending them to me, and thank you again to Allan for his information, without it I wouldn't have known that these were available.

Now for some careful measuring, I'll keep you posted on the results.