Rattling from Toyota ST150 motor

[coronaman]

when motor mainly cold on startup after approx 10secs there is a rattling sound coming from within the engine.It tends to stop the noise after oil pressure shows 1/2 way on gauge.Garage advised it not hydraulic tappet noise,they thought possible slight piston slap.I would thought then the rattle would be heard straight away on starting the motor.If the car has been outside on hot day noise is not as bad ??.I get a slight rattle when the accelerator is blipped.Have had the oil and filter(toyota filter) both changed.
Uses very little oil.Model of motor is ST150 SOHC.If the heater is turned on and warm water flows thru motor the noise gets less by quite a bit. Hope someone can advise.

[andyztouring]

What mileage has the engine done?Sounds like the bigend bearings are on their way out.What code is the motor,ST150 is the chassis code,not engine code,if its the 3S,they tend to wear the bigend bearings,drop the sump and replace the bearings before it damages the crankshaft.

[coronaman]

The motor #is 1S-lu,the local garage mechanic who I trust what he says ,didnt think is was bearing when he listened to it.It is really bad when stone cold,quieter if it has been siiting in the sun.As long as i leave it after startup to sit a we while before driving off it is driveable,but if driving off straight away it sounds like a really bad diesel vehicle.
I have tried using a wooden rod to try to pinpoint the exact position of the noise but no such luck.
I had a local toyota mechanic listen to it when the motor was warmed up and he thought possibly in the cambelt/bearing area.
Ignition timing is set at 8 degrees with t1 and te1 strapped ,vacum reading on motor at idle is 20,no error coding shoing on engine check light.
Thaks for the prompt reply

[coronaman]

Sorry mileage is approx 172000,all good apart from this complaint

[andyztouring]

Have you checked water pump,alternator bearings,power steer pump if fitted for worn /seized bearings,however they would be noisy all the time,timing belt tensioner can get very noisy as well,have you looked at the camshaft lobes for worn lobes/worn followers.Sometimes they quieten down once the oil starts moving around.

[coronaman]

one thing i found that made the engine really rattly on startup was using 20/50 oil instead of the current 15/40.
havent checked the cam lobes etc also havent checked inside cambelt housing also