355 Oil pump chain tensioner replacement

Over the past few months my car ('98 GTB, 38K miles) has developed an increasingly loud noise coming from the front bottom of the engine at the oil sump. Right where the oil pump chain tensioner is (verified with a stethoscope). The noise sure sounds like a chain rubbing on something -- not a knock or rattle. I bought a new tensioner and finally got a chance to dig in this weekend, and hopefully I found the culprit. The pad on the tensioner had walked laterally on its mount and one rail of the chain wasn't really making contact with the pad, allowing the link joints to drag along the pad and make noise. I'm not sure yet whether what I found is the source of the noise, but it would make sense.

I haven't seen any details on this procedure in the archives, so here are some pointers: No need for engine removal. Remove the oil sump, windage tray, oil pump (I had to remove the nut holding on the sprocket on first, then the pump body, then remove the sprocket from the chain) and the forward-most main bearing saddle (two 19mm nuts). With this last step you get to inspect one of your main bearings, and it's necessary to make room for the tensioner to slide off the post. Then remove the 10mm bolt on the tensioner bracket and the circlip and washer on the tensioner post. Then the tensioner slides right off. Pretty easy job actually. I should have it buttoned up in a few days when I get a little more shop time.

First two pics show the original tensioner and how one edge of the chain was basically not making contact with the pad, as the pad has a rounded shoulder.

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This shows how far the pad had migrated. With some force, I could slide it back and forth across the tensioner body with my thumb.
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This pic shows the difference between the original and superseded tensioner. Note how in the new one the pad is secured to the tensioner body with a metal tab so it won't walk.

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A few more pics. The wear on the pad surface was nothing concerning, but the way the pad could move laterally is quite concerning. The stupidity of the original design is pretty amazing. I am basing this off only my own experience, but if you have chain noise it might be worth installing the updated tensioner as part of a major service.

This shows the tensioner post with the tensioner and main bearing saddle removed.
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Rod big ends and crank counterweights -- the view with the windage tray and oil pump removed.
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New tensioner installed with what will hopefully be a corrected, centered chain pathway across the pad.
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Got the car buttoned up today and the new tensioner seems to have solved the chain noise. Haven't taken it on the road yet but running on the lift it sounded nice and quiet.

Took the opportunity to hot tank the sump (I've always secretly felt inadequate compared to @MAD828) so that's looking nice and clean now. Only a few of tips to mention about reassembly:

- The oil pump is held on by four allen bolts; one is just a tiny bit longer than the other three. You'd never notice, and I didn't, and this caused a moment of confusion/terror when I put a long bolt in a short hole and vice versa.

- To get the oil pump on after you install the new tensioner, first install the sprocket in the pump chain with the cutout for the woodruff key at 6 o'clock. Then compress the tensioner to give the chain slack, and slide the oil pump onto the sprocket, lining up the key to the sprocket cutout. Really helps to have a helper here holding the tensioner down. There's a locating dowel at the front left of the oil pump's four bolt holes. Make sure you're seated on that before you start any bolts, and make sure for that one in particular you have a wobble allen to start it. The pump body prevents you getting on it squarely. Not a problem for torquing it, but this can cross-thread it when you're starting.

- Back where the sump bolts up to the transmission, there's an o-ring that runs in a groove. Tack it in place with sealant so that it stays down in its groove while you bolt up the sump.

- There are a couple of o-rings at the mating area of the oil pump scavenge to the pump body. Make sure they're seated in the grooves.


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Thanks Ken -- Threebond 1211

 

Yikes. The chain actually broke? What was the cause? In my case it didn't look like anything catastrophic was about to have happened, but the noise was getting louder and it was ruining my ability to enjoy the car.

 

Good eyes -- yeah, the chain did not end up perfectly centered on the new pad, but the important thing is that the full width of the chain is now running over the flat surface of the pad. Before, the edge of the chain was running over the shoulder of the pad. I've looked at tensioner pad pics in the archives and most show the chain wearing off-center. Seems to be normal. As for the stop plate, I noticed that as well and straightened it. It's just a stamped piece of metal. Don't think it makes any difference. New tensioner and old had the same spring pressure -- I could not tell any difference.

Overall I'm not a huge fan of this system, but it must be pretty reliable since it was barely changed from the 348 through the 360. My biggest complaint is how noisy it is. Even with the new tensioner, my car still makes a lot of chain noise. It's the main sound competing with the exhaust note when you listen to a warmed-up 355 idling. I went through a bunch of BaT 355 videos to make sure I wasn't crazy, and my car sounds like all the others. Lots of chain noise. I took it over to GTO Engineering and asked their top tech to listen to it idling and he said, "Perfectly normal."