30 replies to this topic

[imack]

I think the simplex tensioner can be fitted to duplex set up and work but I don't think it fits properly.

[Wiggy]

I've read a few times that you don't need a tensioner for a Duplex Chain, but why is that?

Just curious.

The early 1275's from 1963 (though these were 1071 in that year) up to 1977-ish had a Duplex set up and no tensioner at all, after which they went to Simplex and with a Tensioner. I've run engines with a Duplex Chain for around 80 000 km while they did have slack, there was no rattle from them.

The 998 and other small bore engines also went to a different Tensioner in 1979. Prior to 79, while having a Simplex, they did have 'Tensioners' by way of 2 Rubber Rings in the Cam Sprocket.

I do prefer to fit a tensoner regardless of the set up as it's that little more 'refined' with less timing scatter at lower revs.

Thanks for the as usual comprehensive reply.

[govig]

David Vizard seems to think a simplex tensioner on duplex is ok. 

 

The question is now about valve timing. Given the chain's initial wear will retard the valve timing after 1000 miles ish, I was going to set it a bit advanced (say 1 or 2°).

 

Does anyone know what is the standard Spi cam timing?

 

This is a 8,000 mile from new motor which went really well with its original injection set up. However as it's now going in a Moke, I've gone to a HIF44 and 59D electronic distributor. That said, is substituting these items any reason, to change the standard cam timing?

[Spider]

The question is now about valve timing. Given the chain's initial wear will retard the valve timing after 1000 miles ish, I was going to set it a bit advanced (say 1 or 2°).

 

Does anyone know what is the standard Spi cam timing?

 

This is a 8,000 mile from new motor which went really well with its original injection set up. However as it's now going in a Moke, I've gone to a HIF44 and 59D electronic distributor. That said, is substituting these items any reason, to change the standard cam timing?

 

According to Factory Data, the Cam and it's timing to the Crank were the same between the HIF44 Carbed Engine and the SPI, so leaving it as is should give the same performance and characteristics as the Carbed Model of the engine.

However, depending on what you want or how you'd like it to drive, there can be some gains to be had by make some adjustments to the Cam Timing, but of advancing it, I'd suggest not advancing more than 6 degrees.

Timing by the way is

In Open  9⁰ BTDC
In Close  41⁰ ABDC
Ex Open  55⁰ BBDC

Ex Closes 17⁰ ATDC

[Cooperman]

It is probably OK to fit a tensioner to a duplex chain with no issues.

However, I have had one high-revving engine with such a set up and the tensioner pad had broken up. On another I saw the pad was breaking up.

Edited by Cooperman, 26 March 2019 - 11:12 PM.

[DeadSquare]

From my engineering days,  ...   Renold  told me that a chain "beds in / stretches" in the first 50 hours, after that, it is wear of the sprocket that makes a chain loose.

[Cooperman]

I don't fit a tensioner with a Duplex as my car is a MK.1. I did remove a cam timing cover after 1500 miles from fitting a new chain and the cam timing had backed off approx .5 degrees. Now I always time in 2 degrees advanced from nominal to allow for chain stretch.

[johnR]

Just a reminder to adapt the timing cover (if not already done) when you've fitted the duplex chain. I found the chain just catches the circular shroud around the vent aperture - probably only needs 3mm taking off - although I removed mine completely then needed to fill and repaint the cover as removing the spotwelds distorted the cover.

[Spider]

Just a reminder to adapt the timing cover (if not already done) when you've fitted the duplex chain. I found the chain just catches the circular shroud around the vent aperture - probably only needs 3mm taking off - although I removed mine completely then needed to fill and repaint the cover as removing the spotwelds distorted the cover.

 

Yes, good point and thanks for the reminder.

 

There's also a dimple in the cover at around the 4 O'clock position that also need tapping out when going to Duplex with the late covers.

[OzOAP]

Had some very poor quality duplex sprockets from Minispares lately. They look very well made, but are 8-9° out on timing.

[DeadSquare]

Had some very poor quality duplex sprockets from Minispares lately. They look very well made, but are 8-9° out on timing.

 

These days, there is no excuse for them not being bang-on accurate   ...   unless there is a computer error.

[Spider]

 

Had some very poor quality duplex sprockets from Minispares lately. They look very well made, but are 8-9° out on timing.

 

These days, there is no excuse for them not being bang-on accurate   ...   unless there is a computer error.

 

 

It helps compensate for the cam error

[OzOAP]

Had some very poor quality duplex sprockets from Minispares lately. They look very well made, but are 8-9° out on timing.

These days, there is no excuse for them not being bang-on accurate ... unless there is a computer error.

It helps compensate for the cam error

I only use Piper billet cams so there isn't any.

[Retroman]

 

Had some very poor quality duplex sprockets from Minispares lately. They look very well made, but are 8-9° out on timing.

 

These days, there is no excuse for them not being bang-on accurate   ...   unless there is a computer error.

 

 

Lost degrees in translation from imperial to Taiwanese...??  hahha

[govig]

There seems to be some discussion how many degrees ATDC the #1 inlet pushrod should reach full lift.

 

Some say 110° and some 106° . As 4° is a fair difference, does anyone have a definitive knowledge of this setting for the Spi standard cam which Moke Spider has said is the same cam as the late 1275 carb version. I intend to advance it 1-2° to account for initial chain wear although not convinced this happens much with a duplex.

 

I have spent some time looking for this info on the net, but it's conflicting and I've got a headache!

Edited by govig, 08 April 2019 - 09:43 PM.