Hiya after timing and installing a new engine in my nb mx5 the engine ran perfect in all tests until it produced to loud metal noise which stopped the engine. checked the cam gears and timing was off by several teeth. did not understand how possible for it to skip timing. removed tensioner and retimed the cam gears. ran fine after several more tests (the car does not drive) and i checked the timing once again after probably 10-30 mins of running and the timing was once again off by several teeth. took the front face off engine all pulleys and belts and even checked the tensioner length and it was okay. cam gear belt is like new as well.
retimed the engine again and checked the tdc on the gear was actually tdc and it was. also replaced water pump gasket as was leaky. retimed again and needed to test the engine to bleed the rad. after a few minutes of sounding like a diesel (which it keeps doing) it then produced a horrid rattling sounding like rod knock but from top end. as well as a screech that got eternally worse with a rev. i think the screech is part of the timing cover rubbing on the water pump pulley. the knock sounded like a bolt dropped in with the cams but took the cover off and nothing. please help?
I have a 1998 1.8 engine mk2 mx5. The engine in the car was built by me from just a bottom end. crank/pistons and all were already installed. Rest of the engine components were from the original engine of the same type (original engine blew up -previous owner shenanigans-)
Are you certain that you have good oil pressure?
Yeah pressures been reading over half on dash
On my nb2 that’s only the equivalent of the oil light going off - the gauge is a dummy (and I think that’s the case for most/all nb).
The scenario going through my mind (and I hope it’s not the case) is that you have low oil pressure on the rebuilt engine (bypass stuck open, oil pump not primed or whatever reason), starving the top end of oil, causing partial seizure of the cams and hence the ‘metallic noises’ and the timing belt skipping teeth. Can you beg/steal/borrow an old fashioned analogue pressure gauge to verify that you actually have decent oil pressure when cranking the engine over with no plugs in? I’d be wary of going any further until this has been done, personally.
Just to check: Did you set the cambelt tension per the manual (1 5/6 turns from the cam timing reference marks)? There are quite a few Youtube videos which wrongly show setting the tension at TDC.
Good luck!
Thanks for letting me know! i had no idea Mazda went with a dummy gauge for the oil pressure. yeah the noise was on every rotation and sounded like metal on metal so could defo be the cams on the tappets maybe. basically engine sounds like diesel tractor.
Next step will be check the real pressure. I am a student full time so may take some days to come back with a result. I will note that when inspecting under the cam cover looking for anything obvious i did visually check the oil channels and nothing seemed wrong there.
I set the timing at TDC but not the tension. I bolted in the tensioning roller in the loosest position for the belt, installed the spring but due to roller being bolted in it did not budge, then timed the engine at TDC and then turned it over manually so that the slack was on the tension roller side. I then released the bolt in the roller causing the tensioner to actually tension the belt and tightened it all back up.
Attached is a video of what the engine starting on idle.
From the video: Check that the lower timing belt covers have been refitted properly and that nothing is catching the back of the crank pulley.
Agree to check oil pressure. NB pressure gauge is definitely fake. Sender is simply a normally closed contact which opens when pressure produced by oil pump. If contact in switch fails then gauge shows good pressure even when engine not turning. After discovering this I’ve fitted a new after market sender which sends a proper variable signal to gauge and has a feed for an oil pressure warning light. Now fail safe.
Yep will defo take all belts and pulleys back off too. have a feeling the timing covers are not installed exactly as should be. very finicky and cheap plastic.
smart stuff man. as said will look into the potential pressure issue. only thing is this noise is completely new. it’s always sounded like a diesel don’t know what was causing that but the loud knock is new. that makes me think maybe not oil issue or if it is an oil issue then something has clogged a channel. most likely tho i’m gonna guess it’s something i’ve messed up when putting it all back together
if i ever get this damn thing running right may have to do like you.
update! tried running engine again and the knock is very distinct and from the exhaust side of the camshaft. ran the engine at idle to listen and it made a noise and clunked off. timing on exhaust cam moved several teeth! HELP??
also found that yes a timing cover was rubbing but this knock and the timing jump are connected
no tight spots in timing either. how is a cam turning individually?
Did you check whether the engine was making oil pressure at cranking speed before running it?
IMHO you REALLY, REALLY need to check that you’re getting good oil pressure cranking with the plugs out before running the engine again. If the oil pressure is low, and the camshafts are seizing under load, then you may already have done damage.
How much oil should i be expecting to see?
Also would like to ask and see about something. i’ve realised these issues have only started since adding in the power steering system. initially it was not on the car and the car sounded fine would rev fine even gave it a little drive round the property and back into barn with no issues then. the power steering pump was run dry by last owner due to leaky pipe. don’t know what adverse affects that could have
Do you reckon the added load of pumping the pressurised system is making say the potential lack of oil pressure situation worse? or is it possible for a maybe damaged pump to sieze or something? pump spins fine by hand but don’t know at pressure just thought might be helpful info
I would expect to see 30PSI+ cranking a cold engine (based on other engines, not Mazda).
The manual gives figures at working temperature:
15-28PSI at 1000 RPM
43-57PSI at 3000 RPM
I’m sure that a failed power steering pump could make all sorts of nasty noises, but I can’t see how it could affect the cam timing (especially if it is only one camshaft that it getting out of time) or oil pressure. My emphasis on the oil pressure thing is to rule it out as the cause, since running the engine to perform other diagnostics will wreck it if low oil pressure is the cause.
Just a hunch - Are you sure that the oil jets were installed in the crankcase when you built it up? (4 of them - one under each cylinder, pointing to the piston.)
Engine was from a working car with good compression. We replaced the sump and auxiliary components from other engine. head was off to clean soot on pistons and give the once over. crankcase was the one part that wasn’t touched apart from replacing its sump.
I have an oil gauge somewhere not sure if it will fit the BSP thread in the block. will look tomorrow. Im gonna guess that you wouldnt actually see any oil reaching the head from just cranking either.
Yeah its defo just one camshaft always the exhaust side. that tick like knock could be a lobe hitting on the lifter. the sound is clearly once every rotation.
Ignoring the noise, logic says that if the timing goes out every time you run it then the belt is jumping. So is the belt the right one and is the tension being applied correctly. Or have I miss understood the situation?
hiya yeah the belt is tight all around and properly tensioned. New belt with no signs of any damage on the teeth like from jumping etc… and new tensioner and new rollers either side. but must have to be jumping somehow as exhaust cam is moving individually
Have you checked the cam itself for a fracture crack? I seem to remember this happening in an episode of mx restorer
