Lotus Elan

Chain tensioner plunger in front cover

PostPost by: ill_will » Tue Nov 14, 2023 11:18 pm

It is a while since I dismantled my engine, and I didn't have any luck finding an answer to this via the search function.

Should it be possible to insert the tensioner plunger from the outside of the timing case, i.e. past the threaded section?

The original plunger I have won't fit in the new removable water pump front housing and I wondered if the hole should be reamed from the outside, hence the question. I found a reference to fettling it to fit, but no detail, if anyone has done it before and has any tips? Thanks.
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PostPost by: promotor » Wed Nov 15, 2023 6:01 am

ill_will wrote:It is a while since I dismantled my engine, and I didn't have any luck finding an answer to this via the search function.

Should it be possible to insert the tensioner plunger from the outside of the timing case, i.e. past the threaded section?

The original plunger I have won't fit in the new removable water pump front housing and I wondered if the hole should be reamed from the outside, hence the question. I found a reference to fettling it to fit, but no detail, if anyone has done it before and has any tips? Thanks.


It is possible with a genuine Lotus waterpump casing but the reproduction standard covers don't let you in my experience - they usually only fit in from the other end so some fettling of the thread itself is required but not the plain part of the bore. I would guess it's probably the same for the removable module covers as it's likely they are coming from the same factory.
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PostPost by: ill_will » Wed Nov 15, 2023 7:52 pm

Thanks
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PostPost by: ill_will » Fri Nov 24, 2023 11:02 am

Does anyone have the spec for the piston/plunger bore diameter in the front cover please? Many thanks.

Currently waiting for a new piston to arrive.
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PostPost by: rgh0 » Sat Nov 25, 2023 12:03 am

Measured up some orginal covers and a new Dave Bean cover and got pretty consistent measurments across them all. The threaded section of the plunger hole is 13.4 mm diameter. The plain section of the hole 13.3 mm.

I just finshed building an engine with a Burton front cover I had purchased a few years ago and the plunger went in OK from the outside also.

cheers
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PostPost by: ill_will » Sat Nov 25, 2023 8:12 pm

Thanks Rohan, appreciated.

I'm hoping the old piston is damaged. It goes fine into the old front cover (which it came out of) but only from the inside, and not into the Burton replaceable pump cover, from either side.
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PostPost by: pianoderby » Sun Nov 26, 2023 4:31 am

I recently put a new tensioner from QED into a Burton front cover and it went in just fine from the outside.
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PostPost by: ill_will » Tue Jan 02, 2024 8:13 pm

The new plunger from QED arrived and measures approx 13.35 mm (verniers.) This was a snug fit in the Burton front cover from the inside, and needed some slight rework to get it to rotate without jamming. It won't pass the threaded section from the outside.

The original piston I had was about 0.1 mm larger, so it may be custom made and the hole in the original front cover enlarged slightly. Thanks all for the comments.
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