A slightly different jackshaft bearing issue

[rgh0]

If you need to recover the block and truely cant get the oversize bearings anymore I would perhaps try the following

1. Bore the bearing tunnel out more and press in sleeves and then bore the sleeves to the correct standard diameter and alignment. A good machine shop should be able to do this and produce an outcome as good as new but cost would be similar to sourcing a good second hand block in the UK at least

The next alternatives are really dodgy / temporary

2. Use Loctite "quick metal" which is a thick paste like bearing retainer with large gap filling properties to fill the gap while holding the bearings aligned with the jackshaft - this will probably work ok if do it with all three bearings but then run a short shaft with 2 bearings, hoping to get front 2 bearings aligned well and could last a reasonale time but in hot, high vibration and oily enviroment I would not bet on how long

3. Use some sort of shim metal as described in other posts to try to fill the clearance gap together with loctite. In general adding loose components into a vibrating assembly is a problem as they work loose eventually and you dont really want bits floating around the rest of the engine.

regards
Rohan

[rdssdi]

"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."

This is an interesting finding. Could my jackshaft (cam) not be fitting because the .020 oversize bearings were fitted? From what I read the O.D. of the bearing is oversized.


I used ACL bearings 3C711S. Maybe the wrong bearings were in the box? Would .020 be stamped on a cam bearing as it is on a main?

Bob

[andyelan]

Hi again Andy

The products I had in mind were Loctite 641 "Bearing Fit" or either of the 638 or 648 "High Strength Retainers"

As I understand thing you've got about 9 thou diametral clearance and all these products will accecpt up to .25mm so you should be ok, however, if there is a problem you can use an activator such as 7471 or 7649. Google "Loctite 638 Specification" for more info. All these product, especially the high strength retainers, are designed to resist the temp and oil environment found inside somthing like an engine block so they'll not come loose, in fact the biggest problem will getting them out agine if ever you need to. Don't use any thing like "metal set" though, that definatly won't work as it's not a proper adhesive. Personally even if the gap was a little outside their recommended spec. I would still uses these products alone in preference to any sort of shim packing or sleeves.

That's about all the advice I can give I'm afraid. I've never had this problem so I can't speak from any actual experience therefor the final decision has to be yours. Obviously finding a set of the correct spec bearings is the ideal answer. If you definitly cant find any, then you might want to ask are the old bearing really so bad they can't be reused. Failing that, it's a salvage like the loctite solution.

Good luck anyway


Hi Bob

I did think about you too when I wrote this reply as I had exactly the same thought. As I understand things though the bearings are normally fitted with about 10 thou interference. If you had mistakenly tried to fit oversize bearings then they'd have been 30 thou bigger than the holes and I'm not really sure you'd have been able to get them in. Also given the difficuilty of obtaining these items, I can't really see this being your problem.

Regards
Andy

[Galwaylotus]

Try Miles Wilkins at Fibreglass Services. What he doesn't know about Lotus and Twin Cams probably isn't worth knowing. He may even be able to supply OS bearings.
http://www.fibreglassservices.co.uk/index.html

[rdssdi]

Just received a call from the "new" engine builder. He reported that the cams were installed by the initial engine builder incorrectly. Apparently he placed them in the wrong sequence. The bearing I.D. and O.D. are of different dimension with the largest placed at the #1 front location.

I knew that some bearings were staggered dimension like this but not the TC / Ford.

The smaller diameter bearing was placed at the very end of the block rather than the front. New bearings are beung fit now.

Bob

[handi_andi]

According to Miles I am up the shit......

Plus according to him Ford only went to 15 over thou on outside diameter

Oh great.....I can see Loctitie before my eyes...

Andy

[rgh0]

Just received a call from the "new" engine builder. He reported that the cams were installed by the initial engine builder incorrectly. Apparently he placed them in the wrong sequence. The bearing I.D. and O.D. are of different dimension with the largest placed at the #1 front location.

I knew that some bearings were staggered dimension like this but not the TC / Ford.

The smaller diameter bearing was placed at the very end of the block rather than the front. New bearings are beung fit now.

Bob

Hi Bob
While the bearings are location specific I dont think it is due to staggered OD or ID size

The front bearing is wide and has two oil holes
The middle bearing is narrower and one oil hole
The rear bearing is same width as front but only one oil hole


I just measured a bunch of jackshafts, blocks and bearings and cant find any design stagger in bearing ID or mounting OD or shell thickness just some tolerance variation. I did not have any oversize bearings in the blocks I measured

cheers
Rohan

[handi_andi]

Bob

I went through the same process yesterday just in case I was being an idiot and it was the source of my problem, as well as checking the data from two different sources. Everything agrees that as Rohen says the holes in the block should all be the same and be between 1.68885 and 1.6895 for all three holes and its just the length that varies.

Cheers

Andy

[handi_andi]

Hello all

Had another look at the bearings I took out of the block and it turns out the ones that were fitted were genuine ford parts and where 10thou oversize despite the holes being 20thou oversize, so seems like someone has struggled to find the correct bearings before.

Cheers

Andy

[rdssdi]

I too was not convinced that the bearings had different diameters. The engine builder has now also confirmed that the diameters are the same.

What we now believe is the front bearing, yes with two oil holes, was either improperly installed or of the wrong diameter from the factory.

He is installing all new bearings and setting the cam and lifters as well as balancing and truing the large end circumference of the con rods.

Bob