Lots of clatter but no damage? How come?

[Scouter]

Several weeks ago, whilst overtaking a bus, I was aware that my engine seemed to rev higher than usual before changing up. I continued my journey with no problem but, on starting from cold. a tremendous clatter suggested a serious problem. After recovery to my local garage, the engine was removed and the heads taken off (I have a 1996 V6 petrol with an LPG conversion and it was running on petrol at the time). Two flattened pieces of steel were found on top of one of the pistons. The heads were sent off to a local engineering firm for the heads to be examined, and to my surprise, were declared to be fine with no damage or faults. The bores were all fine too, so the thinking is that something small, perhaps a ball bearing, washer or something has come out of the injectors and managed to enter the combustion chamber through an open valve where they were subjected to heat and instantly flattened. When they cooled they created the hideous clattering noise on starting up. The brief over-revving might have been the result of some extra fuel being injected at the point that something went wrong.

The heads are now ready to go back on but my garage is unable to find the torque settings and tightening sequence of the head bolts. I can find the info for the diesel engines and the 2l petrol, but not the V6 Petrol engine. Can anyone help me with this or point me in the right direction. I've been without my van since July and missing it greatly, so any help will be greatly appreciated.

Best wishes All.

[g8dhe]

The engine manual is available from the shop I believe ?

[mikeWalsall]

Unlike the diesels the 2litre and 2.5 litre petrol engines are not an interference fit .. so maybe sufficient room between pistons and valves to get away without any serious damage ..

One of the reasons if a cam belt 'goes' on the petrol engines .. you should be able to fit a new cam belt and be on your way ..

[rita]

Unlike the diesels the 2litre and 2.5 litre petrol engines are not an interference fit .. so maybe sufficient room between pistons and valves to get away without any serious damage ..

One of the reasons if a cam belt 'goes' on the petrol engines .. you should be able to fit a new cam belt and be on your way ..

I would imagine that this is more of a problem.


"Two flattened pieces of steel were found on top of one of the pistons"

[Scouter]

Unlike the diesels the 2litre and 2.5 litre petrol engines are not an interference fit .. so maybe sufficient room between pistons and valves to get away without any serious damage ..

One of the reasons if a cam belt 'goes' on the petrol engines .. you should be able to fit a new cam belt and be on your way ..

I would imagine that this is more of a problem.

The two pieces of steel were loose on top of the piston as they had cooled and solidified. So I am left with an apparently undamaged engine and heads (thankfully) but the prospect of a hefty bill. I posted this here as it seems an unusual occurrence that might interest the 'techies'. I was also hopeful that someone might assist with the technical info as the I'm already about £1500 into this I reckon. The cambelt(s) were changed last year so I'm going to risk the belts.

[rita]

I would investigate and find out as to where the pieces of metal have come from before the heads are fitted. Have you changed the spark plugs lately, if so and the plug holes have not been protected it is possible for foreign objects to enter the cylinder/s via the plug holes.

Also might be worthwhile checking that particular piston to make sure that it reaches the same position of the others at TDC.

Good Luck

[Scouter]

The obvious place for the metal to come from would have been the heads which is why they were sent off to the engineering firm for stripping and examination and re-seatting of the valves. That has been done and the heads have been declared A1.

The plugs were intact when they were removed and the bores were unmarked, so the only other source of entry to the top of the piston seems to be either the air filter or the injectors. We think it is the latter (refer to the over-revving in the original post) and when they are re-fitted they will get a careful examination.

Thanks for your 'good luck' wishes Rita. I will mention the reach of the piston at TDC to my garage man.

[rita]

I would also get your mechanic (if they have not already done it)to check the Throttle Body Assy, this could also be the cause of Over revving .

[Scouter]

All good suggestions - and thank you - but my mechanic needs the head bolt torque settings and sequence before anything else. It seems that this info on the V6 engine is not 'out there' in the way that the diesels and 2ltr petrol engine is available.

Still hopeful that someone will pop up and help.

Regards All.

[Bongolia]

Hi Scouter
These head bolts are stretch bolts so you first need to find out if they are the correct length.
If they are stretched then they will need to be renewed, the tightening torque is just a set up torque once they have been tightened to that setting evenly they will need to be marked and tighten by degrees.
It is not as straightforward as tightening them to a set torque.

I think the best advise was that proffered earlier and get a manual from the forum shop or find a garage that has an Autodata database and search under Mazda engine codes for the match to your engine code and work from that, they can print it out.
Maybe your garage knows of someone. I believe they are J5 engines, someone on here will know, it may be in your log book.
As for the belts if its cam belts you are referring to they should not be refitted once they have been run for a while you need to replace them. Wheels and pulleys will be okay if they where renewed last ime but it is mileage dependent.
As for the metal it probably came through the induction system so it needs to be found out where it came from before they turnover the engine it will be after the air filter obviously.
Good luck.

[windywatson]

As above, don't reuse the old cambelt. In comparision to the money already spent the new belt is not that expensive. I expect that you have more investigation to be done once the engine is reassembled. The metal items have to have come from somewhere. It is vitally important that their origin is found should there be anything that is still falling apart somewhere within the induction side of the engine.
For your info, the engine type is J5-DE, & I would have expected the engine specialist who refurbished the head should be able to give your garage the info you need. As they must have had access to engine data to do thier job. I have been looking in my V6 engine manual & the head bolt length measured from the underside of the bolt head should be 107.7-108.3mm. They must be replaced if beyond this length. the tightening Torque 17.2-22.0 N/m.
If you are viewing the engine from the front looking along the block (one bank of three cylinders) the 4 bolts starting at the front along the right H/S are numbered 8/4/1/5 & on the L H/S are numbered 7/3/2/6. If you draw this out on a sheet of paper, the numbers are the tightening sequence for the bolts. When being tightened each one should be tightened to the torque mentioned. Then tightened again by a further 90 degrees each. The workshop manual suggests marking each bolt head with a spot of paint to indicate the amount of turn so as not to exceed the 90 degrees +/-5degrees. Hope that makes sense. Best I can do without being able to post a copy of the page. Bearing in mind the cost of the manual it would be worth getting one asap. Best of luck, keep us posted

[g8dhe]

The bolts are actually tightened by a total of 180 degrees, in two stages not just 90 degrees, it really needs the page with its diagrams to be scanned,but even better get the manual its worth the money!

[teenmal]

Scouter,

Your Mechanic should be able to get all the info they need here.

http://olybrake.com/pdf/fel_pro_torque_specs_guide.pdf

[Bongolia]

Scouter,

Your Mechanic should be able to get all the info they need here.

http://olybrake.com/pdf/fel_pro_torque_specs_guide.pdf

Now that is a useful link

[teenmal]

Scouter ,

Did you get the settings that you required?.