TwinCam Engine - Jackshaft Bearings

[zrxmd]

Hi guys, I need your help again.

I'm restoring a Lotus Elan S2 1964. I'm working these days on the engine. 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", but I have 1.6860". Does someone has seen that before?

Thank you for your help ... sorry about my english!!!

ZRXMD

[elanman999]

Yes I had similar trouble on my 1600 block, one bearing was OK one was a bit tight and one was very tight.
Get yourself some engineers blue and scrape them out.
John

[Dag-Henning]

- it happens all the time..You need to scrape them / ream them out to fit.
I have also managed with a tool to hone ( ?) break cylinders. ( unless it is the middle bearing that causes you trouble...... )

Dag

[M100]

[quote="Dag-Henning] I have also managed with a tool to hone ( ?) break cylinders. [/quote]

I would have thought that using that method the debris from the stones would get deposited in the soft bearing material. Given the bad access, scraping and trying to keep the bearings round is a ballaching way to get clearance.

Even though we are only talking about 3 thou or so, Inline boring, while needing the correct tools and facilities is realistically the only way that will retain the bearing roundness (and do the job in less time than it takes a water pump to fail)

[GrUmPyBoDgEr]

Remove the rear end of the jackshaft with a hacksaw from just behind the second bearing journal. If you know someone with a lathe, get the remaining cam lobes tuned off. Fit the rear bearing shell so that it blanks off the oil supply to prevent leakage.
Then you have only the front & centre bearings to worry about
John

[Dag-Henning]

- true ! - and you get a better fuel-pump too....... Martin; - I haven't actually seen that happen, as the stones do not wear much....It is important though to lubricate with alcohole or similar while running the tool......

Dag

[rgh0]

I agree the problem is relatively common. The issues arises from the combination of tolerances on the block bore, the bearing thickness and the jackshaft bore adding up for too tight bearing clearances. I dont know how Ford managed this during production as supposedly all the components are still to their original production tolerances but it does not work now.

In general I manage it by component selection from a stock of bearings to get the required bearing thickness. If I have to I then resort to regrinding the jack shaft bearing to the bottom end of its diameter tolerance range and accepting bearing clearances at the minimum end of their tolerance range. If all of this does not get an acceptable solution I may end up scraping the bearing a minimal amount. So far I have never had to line bore the jack shaft to increase the bearing mount diameter.

The engines I build these days all use a shortened jackshaft and electric fuel pump which use only the 2 front bearings so this reduces the problem as well as their are less bearings to worry about

Rohan

[GrUmPyBoDgEr]

It's good to have you around Rohan.
I forgot about the lobe for the mechanical fuel pump.
The last Twin Cam I built went into my 23b a looooong time ago
John