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Are my crank and rods ok?

Hello

I not long put a 'rebuilt' engine into my 7, though it started ok, it developed an intermittent knock.

Having mostly distmantled the engine (an early coil) suspecting the front lip to be broken I found it to be intact.

I have a couple of questions, the front mains are the original style ball and a roller and the ball has a good bit of play, presumably this has allowed the crank to move, hence the knocking? The timing gear was firmly fixed also.

Secondly looking at the rods it appears they were new, and are hardly marked, but there seems to be a lot of side play (I.e along the journal, not excessive clearance). no1 has about 50thou, 2 a little less, and 10thou (ish) all in 3 and 4. My red book says 1/16th in end play is ok (62 1/2 thou), so by that my crank has survived, but the range of play concerns me. Is this still useable?

Many thanks in advance

Re: Are my crank and rods ok?

Sounds like a loose flywheel. They should be carefully lapped onto the crank and tightened up VERY tight.

I think most of us have put an engine together at some time only to find a knocking because we didn't tighten the flywheel up properly.

Re: Re: Are my crank and rods ok?

I have got a fair bit of "side" play in my rods. I was worried about this but as you point out it is OK according to those that know! I originally had a very harsh engine and did at one stage think that there was a problem with the excessive clearance but since fitting and adjusting a manual ignition control it runs fairly smoothly so I reckon the clearance is all OK .
I believe a reasonable clearance is required to allow oil out from the big end journal otherwise it would have nowere to go?

Steve.

p.s I did strip the engine 3 times in pursuit of phantom knocks and never found much wrong!!! Refer back to some earlier posts of mine and you will see what I mean!!!

Re: Are my crank and rods ok?

Hello Hedd,

No doubt some of the mechanical gurus who are regular contributors to this Forum will be much better qualified to offer much more constructive suggestions than myself, but, for what it is worth, I don't think the amount of sideplay on your bigends is anything to worry about. I have always thought that side clearance in the order of 1/16" or so is desireable in a non pressurised system, to assist with oil flow. Right now though, I am not certain where I have gleaned that notion from.

I think that Steve could well be right when he suggests that you have a look at your flywheel, as they can, and do, come loose from time to time.

What I would be just a little bit worried about though is your comment that the Ballrace at the front of the engine "has a good bit of play."

As I understand it, a prime function of the ballrace is to keep the crankshaft properly positioned in the crankcase in a longtitudinal sense (i.e. dealing with the "end thrust" on the crakshaft)as well as to help the roller bearing take the up and down loads.

So if you have a "sloppy" ball race, then I would have thought that would need to be put right, otherwise your crankshaft would tend to "float" lengthwise. Not a good situation.

Bearings are relatively cheap, but a fair beggar to get out. If you have the motor on the bench, I would be inclined to replace the front bearings.

I assume by the "red book" you mean the "Austin Seven Manual" by David Woodrow. If that is the case, then I think he gives some very sound advice about front bearings, including the possible replacement of the front Ball/Roller combination with Angular Contact bearings as used in later engines. I don't have my copy to hand at the moment so can't give you a reference, but I am sure you will be able to find it.

Hope the above is of some help

Kindest regards,

Barry R.

Re: Are my crank and rods ok?

Many thanks.

The source of the end float was almost certainly the front ball, I swapped flywheels before fitting it in the car, it was lapped and pretty tight. It also took a fair bit of getting off.

I have had a front steel front lip put on another replacement crankcase, and am currently giving all the oilways etc a good clean ready for the transplant of the engine parts to that (with 3 new bearings). hopefully that should do the trick.

Re: Are my crank and rods ok?

Hedd,

Just a thought, if you are going to use the later type of front bearings with two thrust ball races make sure you put the thrust faces together ( i.e. in the middle ) they should be marked 'thrust'. There os also some usefull information in the 750mc 'Austin 7 Companion' book about the use of these bearings.

Good luck

Malcolm

Re: Are my crank and rods ok?

Hedd

I've had an email from you but the return addy bounces back. can you please contact me again and tell me which part of the addy to delete.....

Sandy Croall
A7CA Registrar

Re: Are my crank and rods ok?

Sandy try hedd_jones@yahoo.co.uk, my work e-mail can get stupid with personal e-mails

Re: Are my crank and rods ok?

If you use a pair of angular contact ball bearings, make sure that they are indeed a matched pair. They are precision ground to give the right amount of preload. Two new bearings taken at random (even from the same maker)may be too tight or too loose, and will require a shim a few thou thick between either the inner or outer faces to correct this. I found this out the hard way, with a rebuilt engine that was incredibly tight to turn until reassembled with a home-made steel shim.