Front cover - timing chain interference.

[elanner]

The engine is now out of my Elan and the engine stripped down to change the water pump. On looking at the front cover it can be seen that, at some time, the chain has been rubbing against it. It's not clear whether this damage occurred with the current engine build or with some earlier engine build - the chain is completely unmarked (but likely would be given that its steel would make short work of the soft aluminium).

So, does anybody have any words of wisdom about this wear? The engine was running fine and making no untoward noises. The chain was not loose. As can be seen, the damage is close to the crankshaft drive sprocket rather than up by the camshaft sprocket.

Thanks,

Nick

[benymazz]

Nick,

I discovered a similar scar on my back plate when I tore down my backup engine too. If anything mine was a little bit deeper than yours. I never saw the engine run (when I laid my hands on it for the first time it had been sitting under a workbench for 35-40 years) but that back plate is now installed in my engine and it seems to be running fine.

It still troubles me slightly as my inner engineer thinks that surely when the timing chest/water pump casing was designed that the tolerances would not have been unnecessarily tight (as the damages we have discovered would indicate). With a chain there is very little tolerance for the various sprockets to be "out of plane" with each other and this is reflected in the endfloat specifications given for the crankshaft, camshafts, and jackshaft.

-Ben

[Concrete-crusher]

Ditto

I also found similar ware marks but didn't worry too much and the engine runs fine.

Steve

[Quart Meg Miles]

As Benny suggests, it might be a rather thick casting which left the un-machined ridges proud but it could be that the engine had a thrust washer failure letting the crank drift back. A few years ago I had one wear so much that the other thrust washer dropped out; if I ever take the casing off again I'll have a look for chain rubbing.

It seems unlikely that the casing attachment bolts came so loose that the plate could distort in both the sprocket and water pump areas where the wear is.

[CBUEB1771]

Nick,
Here is a photo of the back plate from my +2. This one has no marks from chain rubbing which is why the marks on yours jumped out at me yesterday. I am now wondering if there is something odd about the width of your timing chain across the pins. We agreed that it looked fine, but we should check its width against another chain. I think I tossed the one that had been in my engine but I have one or two new ones buried somewhere, I'll find them later today. I'll also bring my backplate to Carl's shop next Wednesday and we can compare the castings.
Russ

[Concrete-crusher]

When I replaced my thrust washers I needed one to be 0.005th oversize to get the end float in spec. So maybe the original was worn, causing the wear I observed

Steve

[RichardHawkins]

My backplate looked similar.

My thoughts are that most of our vehicles went through a time between being new and loved before they got to being old and loved. In this interim period the value had declined to level where young men could afford to buy them, but could not afford to run and maintain them, and they were bodged. My car was 11 years old when I bought it and must have been owned by someone who was very strong, many bolts were stretched including the head bolts. I have replaced every nut bolt and stud in the vehicle.

Just my opinion,

Richard Hawkins

[Quart Meg Miles]

My car was 11 years old when I bought it and must have been owned by someone who was very strong, many bolts were stretched including the head bolts. I have replaced every nut bolt and stud in the vehicle.
Richard Hawkins

Most young men didn't have torque wrenches and 65 lb-ft is no big deal.

Back on topic, a wide chain sounds like a strong possibility; does the racing fraternity use them?.

[rgh0]

Chain widths are standardised and the next wider chain would probably not fit at all so unlikely to be the chain itself. If building any engine you just need to ensure you buy a quality chain with solid rollers from a reputable company not a cheap chain with rolled rollers that have a seam in them. Chains that have a removable link which should not be used are slightly wider where the link clip fits and this could possibly cause contact

IN general contact and wear on the back plate and cover is possible as the clearances are tight and the stack up of fore / aft tolerances on the many components that locate the chain versus the cover is significant. The use of wrong components or incorrectly machined components can add to the problem. Also other things such as a loose chain can cause the chain to move around.

it was really a miracle that Lotus managed to find enough space to squeeze in the twincam chain drive so some compromises are to be expected

cheers
Rohan

[2cams70]

Unlike most modern engines the head is not positively located by dowels in the block. There's a fair amount of slop around the head bolts, the head bolt holes and the three top timing cover bolts that pass through the head. If the head is fitted in such a position that it is located far rearwards the cam chain will be taken with it and moved closer to the backplate. Best to push the head further toward the front of the block as the location "slop" allows before final tightening.

The crankshaft thrust washers are generally very long lived provided the clutch pressure plate is not an especially "heavy duty" type with high spring loads. Wear would generally show as noise and would have to be pretty bad to cause that type of movement of the chain. Early thrust washers on the pushrod engines had a Whitemetal facing and are unsuitable for anything that's high performance. All of the replacement thrust washers are now copper faced and durable. You'd only get the Whitemetal type as NOS these days and they'd be very old!

Although unlikely check the crankshaft chain sprocket too to confirm the correct twin cam type is fitted rather than the regular pushrod type. They are different! Check too that the spacer between the jackshaft and it's sprocket has been fitted.

That picture shows more than just a "touch" of the chain so something in the assembly is likely incorrect.

[1owner69Elan]

Just a comment on ?slop? in the head placement.

When I fitted a new SAS Weber head to my original Lotus block, the engine builder precision milled two locating 17/32? dowel holes in the head and block.

Would seem like a recommended practice if you can manage it.

[2cams70]

If building any engine you just need to ensure you buy a quality chain with solid rollers from a reputable company not a cheap chain with rolled rollers that have a seam in them.

I checked the chain I bought from QED and it has rolled rollers will seams in them. Does anyone have any experience of timing chain issues with chains that have seamed rollers?

The chain has the manufacturer name "IWIS" stamped into it. IWIS are an OEM supplier and possibly the largest manufacturer of automotive timing chains. I doubt there's a problem but would be interested to know otherwise.

[elanman999]

I have just rebuilt both of my twinks, one tall block the other std. The chains that came off were both Regina split roller chains and the chains that went on were Iwis split roller. One of the old chains will have done about 45K miles and the other about 35K. Both were in good condition. Only changed them because while you're in there why not.
Cheers
John

[JonB]

What's the expected life of a cam chain given on road use?

[avro]

I had a look at about twenty old back plates and the two pictured here were the worst of the bunch. Looking at the wear pattern it would indicate a problem higher up within the cam chain drive and more likely to be the position of the cam sprockets rather than that of the crank sprocket.
On closer inspection l was quite surprised at the variation in certain measurements that could position the cam sprockets further back.
I looked at a number of heads and found a variation in measurement of .021? between the centerline of the head stud holes in the casting and the machined groove that holds the cam in position.
I also found having measured quite a number of camshafts that the distance between the sprocket mounting face and the annular ring varied by a surprising amount. One being .018? less.
Couple this with the fore and aft movement of the head casting on the cylinder head bolts because of the lack of locating dowels and it?s not surprising that we see this on some engines.

Nick