I have bought a 2008 mx5 2.0 with 35,000 mile on the clock today as a non runner, I bought it at an auction, It was driven in to the auction with no problems, and then they said the engine had seized , I have got the car home, jumped it, and it was solid, I rocked the car to see if it had seized, and the main pulley turned, I then noticed the main pulley bolt was loose. I could turn the bolt with my hand, can anyone tell me how the main pulley set up works, is it on a taper for the cam belt timing, because at this moment the cams are not turning, I think it has lost the cam timing due to the main pulley coming loose, it could be the cam belt , but I don’t think so, I am thinking the pistons are up againsrted the valves. or am I barking up the wrong tree. any help would be appreciated.
An off the wall thought, one that might not be so expensive to fix.
Many years ago my ancient Mini had the same apparent problem, couldn’t be cleared even by rocking the car back and forth in gear, but it turned out that the starter motor had worked loose and the Bendix gear (Drive Pinion on MX5 with modern pre-engaged starter) had jammed the ring gear on the flywheel. That was fixed with a new gear on the starter motor because the ring gear was not as badly damaged (although thereafter when cranking it clicked as it went round, ouch).
Bear in mind that the Mk3 cam chain pulleys are all inside the engine and unless the chain or tensioners have broken (expensive) it should not be problem.
the mk3/3.5 engine has a timing chain. The bottom pulley AND timing chain gear free wheel on the crank shaft and is held in place by the bottom pulley bolt. If the bolt is loose it will allow the crank/Pistons to move and not the valves…hence contact.
the chain can be in tact but not in sync with the crank shaft.
Hi Paul Thanks for the offer of some help, First of all I think the car I have is a 3.5, not sure If that makes any difference, I also have 2 mk2's 1.8 MX5s as well, I am a bit of a car fanatic, I have lots of car,s and I liked the look of this one, where do I start with this car, How is it set up. the bottom pulley is loose, and they tell me it is chain driven, so how can I have valve piston contact, how can the bottom pulley turn without the cams? unless the chain has snapped or is that pulley on a taper and not a key, that's if it is part of the valve timing gear.
Paul, the engine drives the crankshaft. The crankshaft drives the cams via the chain. Timing is critical to avoid valve to piston contact. If the engine turns with no cam, the pistons will hit the valves.
Good point, but I thought there was no external access to the inside pulley for the chain, just the accessory pulley. Which pulley is he referring to?
Having just looked at the exploded diagram for the engine I cannot see any way that the crankshaft sprocket is locked to the crankshaft other than the tightness of that one bolt. Surely not? There must be a key or spline. If not then I see what you mean by a floating pulley.
Is this my engine? if so I can see what has happened, can someone explain to me why this bottom sprocket is not keyed, you are just relying on the main pulley bolt, to tight enough to hold it.
I’ve rebuilt many older simpler engines but would not fancy this. Talking to friends who still work in the trade they tend not to be rebuildable unlike the old days when you’d have a regrind and new shells or a rebore and new pistons apparently its new assemblies if you can get them but hopefully it may not come to that.
I’d definitely take rodders advice and help as he will have done lots of them