Bottom end knock

[Bill Reed]

I have fitted spin-on oil filter and also added Wynn's on last oil change but I still get a severe knock on start-up unless I turn the engine over a few times with the choke in before starting. Knock disappears when oil light goes out. Even when warm the knock returns on re-starting after the engine has been stopped for half an hour or so. The oil pressure warning light actually flickered a couple of times on tickover the other day after a 25-mile run, though this hasn't happened again. Advice please!

Bill Reed member 7393-05/07
1974 2500TC

[Alan Chatterton]

normal I'm afraid Bill !

The knock is due to excessive wear of the bottom end bearings (bigs and mains) and also maybe the oil pump.

If you think it knocks badly now, imagine how bad it might be without the spin on filter!!

The problem with these engines is with the traditional oil filter canister is that when the engine is turned off, the oil falls out of the filter and back to the sump. So, when you start the car, the oil pump has to fill the filter canister (a pint or so) before it gets oil to the bearings....... this is the knock you hear...... its the big ends knocking as they have no oil around them.

The filter conversion kit means that the filter now points down, and also has a one way valve in to stop the oil draining away. So, when you start the car the oil pump can get oil to the bearings immediately...... hence no knock.

If you have a filter conversion on, and you still get a knock, then it may be that the damage has already been done, and there is excessive wear to the bearing shells. In which case, you need to drop the sump, and replace the big end bearings, the main bearings (and whilst you are there you ought to do the oil pump and the thrust washers....... consider, pop the head off and do the rings too?)

However,.............. it might be you filter at risk. Is the filter pointing down towards the road, or is it sticking up in the air. On my old 2500S, due to the cant of the engine, it wouldn't fit pointing down, it would only fit pointing 45 degrees up. This means that oil can now fall by gravity out of the filter and we are back to square one again.

Chris Witor supplied oil filters, I believe, have a one way valve to prevent oil loss irrelevant where it is pointing.

So, question is....... how is the filter mounted, where did you get the filter from, what is the general state of your engine, and do you have an oil pressure gauge..... and if so, what is it reading hot running and tickover.

Sorry Bill...... long answer, but it might not be all bad!

[Clifford Pope]

I'd have thought oil would syphon back into the sump regardless of filter angle, unless it had a non-return valve.
I thought the point of a non-return valve was to retain oil up in the block passageways as well as just in the filter?

[David Withers]

I think Cliff makes a valid point. Probably the majority of modern engines have their spin-on filter pointing downwards but almost all (if not in fact all) of these filters now have the one-way valve, which is the rubber flap that can be seen when you look through the holes in the end plate.

CW initially supplied spin-on filters without the valve, but those filters were made specifically for some Nissan engines which had the valve built into the engine. He changed to the valved type a very long while ago after I brought to his attention one of his very rare oversights.

Though a knock in an engine fitted with a spin-on filter may be due to worn bearings or oil pump, there might also be excessive wear of the crankshaft journals which simply replacing the bearings and/or pump won't cure. I'd be inclined to strip and examine the bottom end of the engine before coming to any conclusions.

Unfortunately, additives such as Wynns are more likely to add to any problem rather than cure it. For instance, an oil-thickener might bung up the microporous filter element. I dislike non-approved additives with a vengeance!

Incidentally, with regard to Alan's comment, the 2500S engine in my ex-PI has its spin-on filter hanging downwards, a few degrees off vertical. I did relieve the adjacent flange of the 'chassis' when I first fitted it, in case the engine reaction under sudden load caused a foul, but that relieving wasn't in fact necessary even with the engine canted and set over to that side exactly as in the 2500S cars.

[CAR]

Incidentally, with regard to Alan's comment, the 2500S engine in my ex-PI has its spin-on filter hanging downwards, a few degrees off vertical. I did relieve the adjacent flange of the 'chassis' when I first fitted it, in case the engine reaction under sudden load caused a foul, but that relieving wasn't in fact necessary even with the engine canted and set over to that side exactly as in the 2500S cars.

I have done just that too David and the filter has only ever shown any sign of touching when the rear mounting at the gearbox collapsed allowing more engine twist.

I have these filters on both cars and although fitted with CW filters (with anti whatever valves) I still think it doesn't hurt to have them hanging vertical if possible.

Colin.

[Mike Stevens]

It's pretty safe to say that the knock is due to low oil pressure, especially as you have seen the oil light flickering (however, the oil pressure switch is prone to semi-failure this way).

One thing - how long does it take for the oil light to go out on a cold/warm (warm after a short delay)? If a long time (say more than 3 seconds or so) I'd be suspicious of the pump draining back itself. I had this problem on my PI when I used low cost oil. If the car was left unused for a few weeks, it could take 20 seconds+ for the oil pressure to come up (I have a gauge fitted). I have changed to VR1 oil and the problem has gone away completely. However, I still think I have a poor oil pump.

The pump is of course in the sump, so by the time you've got to it, you might as well at least have a look at some main bearing shells. If they are original I suspect they are through to the copper and a new set (big ends as well) would not come amiss as well as a new pump.

Changing the shells in-situ is not a bad job (I have done it) except for the oil dripping on you while lying under the engine! Also the front suspension has to come off first. You can change all the shells, but remove the fan belt or you will struggle to get the upper, front main shell out.

I believe that the 2.5 engines put more stress onto the main bearings due to the longer stroke.

Cheers,
Mike.

[Bill Reed]

Many thanks for your prompt and full replies. I will report on progress!
Bill

[dallliiisss]

I have fitted spin-on oil filter and also added Wynn's on last oil change but I still get a severe knock on start-up unless I turn the engine over a few times with the choke in before starting. Knock disappears when oil light goes out. Even when warm the knock returns on re-starting after the engine has been stopped for half an hour or so. The oil pressure warning light actually flickered a couple of times on tickover the other day after a 25-mile run, though this hasn't happened again. Advice please!

Bill Reed member 7393-05/07
1974 2500TC

I did a bit of experimentation on this a while back. Although I have start-up rumble on my 2.5 Pi I wouldn't say it was a severe knock by any means, but still a cause for concern. I found the use of a lower viscosity (10w40) oil almost diminishes the start-up rumble, but, the drawback - certainly in our old cars - is excessive oil consumption while using low viscosity oil. I went back to 20w50 oil very quickly.

I think if you can get a few turns on the starter before firing helps, certainly from cold. I don't appear to get as bad a rumble from starting up again a few hours later as I do first thing when the car hasn't been used for a few days etc...

[David Withers]

I'm fairly sure Triumph used to advise that 2-3 seconds of rattle on start-up was nothing to worry about. I believe that advice was in answer to questions raised about Herald engines, but could be read across onto ours.

[VitesseEFI]

There is another possibility - and the fact that you report that the knock is present again after standing for a relatively short period of time matches my experience.

There are two versions of the spin-on filter housing. The early ones had two fixed seals - the usual square section outer one (as used with the standard filter bowl) which keeps the oil inside the engine and a round-section inner o-ring which seals the incoming, unfiltered oil flow from the filtered outgoing flow, each clamped against different machined lands on the block. The problem was, the original filter design meant that Triumph had no reason to tightly control the relationship between the two sealing lands and consequently they vary quite alot. This meant that you could find that the adapter apparently tightened to the block, but leaked vigorously because it had bottomed on the inner O-ring first (and graunching up the bolt could have the dire consequence of pulling the threaded boss right out of the block!). Alternatively, it might tighten up on the outer ring first but not compress the inner ring, leaving an internal leak path for unfiltered oil into the filtered oil. You wouldn't notice this.

To get around this Mocal supplied two different section inner O-rings and a procedure for determining which your engine needed. Something probably often only spotted in the event of an external leak!

The internal leak can have another consequence. By effectively bypassing the oil filter, it allows the oil galleries to drain down much more easily, and thus more quickly, when the engine stops and consequently take longer to refill on restart.

I had this issue with my PI. When I got it it took ages to get oil pressure from cold and sounded nasty, in spite of a spin-on conversion, downward pointing filter and non-return valve in the filter. I assumed the bottom end was worn and indeed the shells were quite worn. However, even after new shells and re-toleranced oil pump it was little better, even though the oil pressure (once it arrived) was excellent. I know the spin-on conversion can work as my Vitesse gets oil pressure very quickly.

I mentioned this to Chris Witor who suggested I check the inner O-ring and so I did. The small section one was found to be fitted and completely uncompressed, with measurement confirming that the larger one was definitely needed. Once fitted, oil pressure now appears after just 2 - 3 seconds even after standing for weeks. Pity the bores/rings are shot!

The later type of conversion has a more complex, self adjusting arrangement with a flat seal on a spring loaded plate. This is supposed to work better, but I've never had one to examine.

Worth a look maybe?

Cheers

Nick