Lotus Elan

A slightly different jackshaft bearing issue

PostPost by: handi_andi » Tue Sep 15, 2009 7:54 pm

Evening all

I have finally got my block in a suitable condition to start reassembly and decided I would start by inserting the new jackshaft bearings as it seemed logically to do this first without anything in the way. Turned the clock on the engine stand to make access easy, unwrapped the AEC3037 STD (AE Federal Mogul) jackshaft bearings I had sourced, put the middle one in the hole and line the oil passage hole up and pressed the bearing so it would be firm in the hole before I gently drifted into place, only to be surprised by the bearing passing all the way through the hole and falling out. Have checked the other two bearings and all three bearings appear to pass straight through their respective holes in the block. The bearings are a perfect fit on the jackshaft, as checked each one on its respective jackshaft journal before attempting to insert, given problems reported by other owners once bearings have been inserted. Measuring one of the bearings shows that the outside diameter of the bearing is 9thou smaller than the diameter of the hole it is meant to push fit into.

Has anyone else experienced this and if so what did you do? Unlike the bearings that came out that were a ring that wasn't joined at the ends, these bearings are made from a loop that locks together like a jigsaw puzzle at its ends so there is no chance of opening the bearing up a little by the looks of it, and yes I have tried pulling.

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Andy
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PostPost by: andyelan » Tue Sep 15, 2009 8:14 pm

Hi Andy

Just a thought but Ford main bearings come in two different outer diameter sizes. Could the same apply to the jack shaft bearings??

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PostPost by: Frank Howard » Tue Sep 15, 2009 8:15 pm

Andy,

My solution when I rebuilt both of my Twin Cams was to leave the original Jackshaft bearings in. They were designed to support a cam operating 8 valves, the fuel pump, the oil pump, and the distributor. Living in a Twin Cam, they have been asked to support a cam operating the fuel pump, the oil pump and the distributor only. On some cars the cam doesn't even operate the fuel pump any more. In other words, they are doing far less work then Ford designed them to do. Even if there is a little wear on them, think about it. What is the big deal? Frankly I've never heard of a Jackshaft failure in a Twin Cam. They're just not asked to do that much as opposed to the overhead cams. For those cams, I replaced the bearings on both engines.
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PostPost by: handi_andi » Tue Sep 15, 2009 8:34 pm

Frank

Thanks for the advice. The bearings I took out were badly scored, as were all the other bearings and by the looks of it there has been metal pieces flying around in the oil, which was also the opinion of the local engine man, who happens to be a twincam enthusiast, when I showed him the big end shells and the pistons. Hence, I woudl prefer to change out all the bearings just to make sure everything is ok, despite the fact that the bearings are not under any particular load as you pointed out. Just couldn't live with knowing that I had installed sub-standard parts, plus my approach with the engine has to always been to stop and seek guidance on here when I am not sure.

Have to admit I am puzzled by the 9thou difference and am wondering if the jackshaft holes have been counterbored at some to be around 10thou oversize for some reason. Have ordered another set of bearings from a different manufacturer to see if that solves the question, would just like to get to the bottom of what's caused the problem before continuing particularly if I face the same problem with the new bearings when they arrive.

Cheers

Andy

PS Think the rebuilt engine will be getting very regular oil changes, despite the low number of miles I did do since the last oil change. Am starting to think around every 500miles....
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PostPost by: types26/36 » Tue Sep 15, 2009 8:37 pm

Andi, I like Frank have never had to replace the jackshaft bearings even when I've worked on OHV Xflow motors but thats water under the bridge now you have removed them, I keep a set (should I ever need them) so I just went and measured the outside dia. It may give you a reference point, just to note they are still wraped in the plastic so make an allowance although it wont make a great deal of difference.
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PostPost by: handi_andi » Tue Sep 15, 2009 8:52 pm

Brian

Thanks for taking the time to measure, photograph and post your spare set of bearings the results are rather interesting.

My bearings, without plastic, have an outside diamter of 1.694"

The holes are showing up as 1.703" diameter.

Given that errors are always possible in measuring internal diameter then I would say yours would be an interference fit in my block although not necessarily as tight as the ones I taped out. Does seem my new AE bearings are undersize though, which perhaps explains why Burton Power have changed supplier for jackshaft bearings.

Will be interesting to see what my second set of bearings measure in at.

Cheers

Andy
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PostPost by: andyelan » Tue Sep 15, 2009 9:07 pm

Hi Andy

Just checked the Burton Power catalogue and I was correct in that cam bearings for the X-Flow and Pre X-Flow are available in two sizes, Std. C3037S/STD and +20 thou on OD FP620. I would suggest your block has been bored to take the larger OD.

This wouldn't be un-common and could even have been like it from new. Ford would occasionaly re bore bearing location diameters and fit oversize bearings as this would salvage an otherwise scrap engine block.

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PostPost by: handi_andi » Tue Sep 15, 2009 9:48 pm

Andy

Your call on this would seem to be correct, as just tracked down the following post on here from some time ago:

"I inserted new jackshaft bearings in the engine block, but they were too tight because the jackshft did not want to go inside the bearings. YES! I've bought the good bearings for the engine and YES! I have the tool to do the job. I removed the bearings and I checked the inside diameter in the block, it should be between 1.6885" to 1.6895"


The interesting thing is the quoted block diameter range given i have just remeasured my block holes as accurately as possible and am getting a reading of 1.710", which is around 20thou over size from the mid-point of the quoted range.

Time to change the order with Burton Power and hope that they still stock the 20thou oversize ones.

Thanks Andy, knew someone would know the answer on here

Cheers

Andy
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PostPost by: handi_andi » Wed Sep 16, 2009 11:30 am

It appears that +20thou on OD jackshaft bearings are in short supply. Has anyone heard of any supplier with some or any alternative ones or a good fix for the problem I have of a +20thou hole and standard bearings, I really would prefer to not refit the old ones as I am not convinced they are plus 20thou anyway

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PostPost by: paddy » Wed Sep 16, 2009 11:43 am

Have you tried QED?

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PostPost by: handi_andi » Wed Sep 16, 2009 11:52 am

Paddy

Thanks, the simple answer is Yes. I tried Burtons, then Susan Miller, then QED and had an amusing conversation with them. At the moment I have the parts man from Paul Matty's on the case and if that fails I will have a word with the local engine man and see if he can find some or has something in his collection of lotus parts. Just thought I would put the word out on here in case anyone has heard of a cash of them somewhere or been able to get hold of a set recently, on the grounds of nothing ventured nothing gained :lol:

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PostPost by: andyelan » Wed Sep 16, 2009 5:27 pm

Hi again Andy

You could always loctite the bearings in place. I know it sounds like a bodge and I've not tried it myself, however, this is an accecptable salvage technique in industrial plant, to recover worn or damaged casings, so I can see no reason why it shouldn't work. You'd need the correct "Bearing Fit" grade of Loctite and, with so little interference between bearings and block, maintaing true alignment could be difficult. It might be worth a thought though if you're really stuck and have no other option.

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PostPost by: handi_andi » Wed Sep 16, 2009 8:36 pm

Hi Andy

A great idea, as you say there is the alignment issue though. What would you think to a strip of 12thou thick copper tape bent around bearing and a little larger than it. Bearing slide in, then excess width of tape snipped and bent over as little tabs to hold it in place and then loctite around the edge to creep in and lock everything together?

Cheers

Andy
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PostPost by: andyelan » Wed Sep 16, 2009 9:57 pm

Hi Andy

That a posibility but I'm not sure how well loctite would be drawn into the gap.

An alturnative might be to centralise two bearing with pieces of shim then loctite the third in place using the jack shaft as a mandrel. Once that's set (24 hours) repeat with the next bearing and so on.

Truth is we're probably over complicating things.

I recon, with care, you could loctite all the bearings at once without a problem. Put the jack shaft in place strightaway to centralise them then keep turning it carefully as the loctite cures just to make sure nothing tightens up. This what I'd probably do.

Just don't glue the jack shaft to the bearings :wink:

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PostPost by: handi_andi » Wed Sep 16, 2009 10:29 pm

Andy

The glue it in and wait for it to cure using the jackshaft bearing as an alignment tool was my original plan after your previous post. I then went looking for the right type of adhesive and found that the potential gap would be greater than the maximum gap capacity. Plus the cure time would mean I would be stood there turnign the jackshaft for quite some time LOL

I agree the Loctite might not creep in, therefore my modified plan would be to coat the bearing, the shim and the block before assembly and cleaning excess off block and bearings as it would cure anyway unless the conditions are anerobic.

Testing with feeler gauges tonight looks like need between 10 and 12 thou all around bearing, so am thinking 12thou copper, which will give slightly on pressing in of bearing should be about right. I know steel might be better just harder to get in right size etc and harder to work with.

Just want to make sure I get a solution I am happy with and can live with, particularly given the amoutn it is costing to rebuild the engine and havent even touched the head yet. Am starting to get the feeling it was recently rebuilt but may not have been assembled with any assembly paste and therefore a certain amount of damage was done on initial start up.

Cheers

Andy
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