BSA A70L Lightning - Engine Part 11 - Crank and Rods

In this episode we begin the engine build - first stop - rods on the crank.

[@matthewharmer1656]

Nice,I always use Loctite on the nuts and bolts,love the big lump hammer!!!

[@markpedwell1250]

I'm in the middle of a a65 rebuild it's a big learning curve, thank god I've found some old boys to help me

[@BSAPowerSet]

Yep, there’s plenty of those and getting older by the day!

[@supadonk1]

A very thorough vid and promotes what most builders say about cleanliness and oil muchio gracius.

[@BSAPowerSet]

Many thanks for the interest and kind comment Marshall.

[@supadonk1]

@@BSAPowerSet Hi I am rebuilding a 1968 A65 thunderbolt where can i get info on method for shimming the crank thanks

[@BSAPowerSet]

@@supadonk1 Hi Marshall - there's articles on forums/sites such as Britbike.com and the BSA Owners Club (bsaownersclub.co.uk), videos of measuring end float on KZbin (Paul Henshaw) and also the factory workshop manual. The important aspect is to measure the end float accurately before then adding shims as necessary to the shim cup on the drive side behind the rotor I believe. I can't show you this as the method was changed for the A70 so any reference on my vids on this subject does not apply to the A65. Hope this helps.

[@supadonk1]

@@BSAPowerSet Yes I looked at your vids and realised the A70 was different thanks for the reply

[@maaseyracer]

I own an A70L engine. I went looking the other day and found NOS rod bearings claiming to be specifically for the A70L. Is there any difference from the A65 rod bearings?

[@BSAPowerSet]

Hi Eric the bearings are the same as the rods are the same as A65 albeit the later ones with steel end caps.

[@geoffgreenhalgh3553]

I would have squirted oil through the oil holes.

[@BSAPowerSet]

Hi Geoff fair point and I intend to do this by priming the engine on rollers to ensure oil is being fed and returned and we have pressure before firing up.

[@richardguy8879]

no oil on the threads before torquing up ?

[@BSAPowerSet]

Thanks for the comment and interest Richard. No I don’t - more like loctite if necessary. What’s the benefit of oil? Cheers.

[@gorblimey61]

In order to keep the rods centered in the bores does it require any shimming or machining with the A10 crankshaft?

[@BSAPowerSet]

Hi and thanks for the comment and interest. It's not an A10 crank - the A70 had its own crank specially developed for it. I agree that A10 crank conversions for A65s were relatively common in racing circles to bump up capacity, but not so in this case, and, in fact, were not officially allowed for AMA homologation purposes.

[@gorblimey61]

@@BSAPowerSet You're absolutely correct! I had mistaken your build with someone else's A70 project. The owner was unable to source an A70 crank so he used a modified A10 crank instead.

[@stevewanless2285]

Angus, another great video. Thank you. I notice that your left hand (drive side) con rod did NOT have the oil release holes that A65's do. Is that an A70 'feature' or did BSA stop fitting the drive side con rods with the oil holes at some point in the engine's history? I tried to research that, but came up empty handed. All I can see is that the left and right A70 con rods had different part numbers 71-2673 (L) and 71-2677 (R) but can't see the difference. Did you have the alloy top half of the rod polished? Thanks for your help.

[@BSAPowerSet]

Hi Steve - the rods are the same as the late type A65 with steel big end caps and the LH rod definitely has the oil holes as it should have as you quite rightly say. They’re difficult to see at the best of times but definitely there as in all honesty I did not know about them until I noticed and had to research myself. When I had my A65 in the late 70’s I never stripped the bottom end on that so was unaware.

[@stevewanless2285]

@@BSAPowerSet Thank you very much for the reply Angus. Much appreciated. The 1972 A65 I am currently rebuilding is a very late engine number (August 72) but doesn't have the steel end caps. I wonder when they were phased in by the factory. I think that A65 production stopped after Feb of 1973. Every now and then I see A70 con rods for sale (on Ebay) often advertised as matched pairs but without the holes in the left rod. I suspect they are Triumph T140 rods. Anyway, my alloy rods look like they have been 'grit blasted' to give a rough finish. I am debating about polishing them or not.

[@BSAPowerSet]

@@stevewanless2285 Hi Steve. I would not use those rods - them being blasted smacks of something more sinister being hidden or masked. I’m sure the factory never manufactured A65s into 1973 - yours would be one of the last - Aug/Sept ‘72. Last BSAs built at Small Heath were the ‘73 model year B50MX.

[@stevewanless2285]

@@BSAPowerSet Thank you Angus. I am pretty sure that I am the first to open the crank cases on this bike. The rods haven't been blasted, but I am just trying to give an idea of the 'rough' (as opposed to mirror polish) finish on the rods. Here is an example of what I am talking about on ebay : www.ebay.com/itm/1971-BSA-A70-RARE-NICE-USED-PAIR-alloy-con-rod-with-steel-cap-71-1105-71-1106-4/174250095784 My rods look like the upper alloy finish on this item.

[@stevewanless2285]

Angus, I apologize. I just watched video number 12 and you address the oil ways there. My understanding is that the oil ways in the left hand rod are there to relieve the oil pressure after lubricating the big end bearings. The oil pump is pressurizing oil through the main bush into the crank and to the big ends. The left hand rod then sprays pressurized oil out into the case and up onto the underneath of the piston skirts, likely lubricating the gudgon pins. One of the differences between the A70 and A65 is that BSA upped the pressure of the system from 50 psi to 75 psi (same as your Rocket 3). That's controlled by the pressure that the Oil Pressure Relief Valve operates at, venting excess pressure into the crankcases. In that Ebay link I posted above, the seller indicates that later engines did away with those oil ways in the left rod. I don't believe that (don't believe everything you read on the internet). Without those oil ways, the oil in the left hand journal can only escape through the bearing. I expect that would raise the temperature of the oil in that bearing to the point when it no longer lubricated.

[@jotomoto62]

I recognize you didn't check any tolerances , like with plastic gauge. Isn't it necessary?

[@BSAPowerSet]

Hi - normally I would check tolerances, as already done with the plain bush main bearing; however, with the big ends, these have been re-ground specifically to -30 by a specialist company (SRM) who know their stuff with these engines, so no need in this case. Thanks for the interest.

[@jotomoto62]

Hi! The A70 has caugth my interest because of the crankshaft shims sitting on the outsideof the crankcase. I have concidered a similar modification to my own Engine.I look forward to see your progress.Torbjörn

[@jotomoto62]

Hi again! I see. I'm also interested in how the cranks plain journal is different to the A65,is lenght of the journal shorter? Torbjörn

[@BSAPowerSet]

@jotomoto62 HI Torbjorn - thanks again for interest. I'm not aware of crankshaft shims sitting outside the crankcase - only on the inside of the thrust bearing but I'll check. Crankshaft side to side tolerance within crankcase would not be addressed by shims outside the crankcase.

[@BSAPowerSet]

Re the crank plain journal, I believe that this is the same size; however, the crankcase plain bearing is slimmer as the shoulder is not present as on the A65 bearing. I don't have an A65 crank though to compare so can't be certain.

[@datadavis]

Fuck, the only guy on the internet documenting the internals of the a70 and the fury and its a bloody chronic lip smacker. Im so annoyed i cant think straight! I dint even remember my name anymore after all that lip smacking.

[@BSAPowerSet]

Thanks for the interest and the comment David. If you could clarify what you mean by lip smacking in this context, I'll try and address that in the future as I'm relatively new to this - getting old but always learning!

[@datadavis]

@@BSAPowerSet oh, there was supposed to be a few smileys in there😄 Not really that annoyed actually

[@BSAPowerSet]

Hi again David. I've just edited the next video and now I understand exactly what you mean! Never noticed it before. So apols the next video contains the same habit, but I'll focus on addressing in the future.

[@derek6580]

Hey man, just a bit of advice. You should really cut your videos. You’re turning a 2 minute video into a hour and a half video of rambling and hesitation.

[@BSAPowerSet]

Hi Derek thanks for the feedback. Yea appreciate I do tend to do that but this is a warts and all so you get my hesitation and thought process thrown in. Some days are better than others.