At the end of my last blog post "It started out so well..." I mentioned a concerning noise emanating from the top of the engine. The engine was making a clack clack clack sound from the cam belt end, as if the valve clearance on one valve was way too large. I reached out and posted a video over on the xweb forum and received a number of suggestions.
Apart from checking the valve clearances it was suggested the OEM resin cam belt wheel could be a cause, they can age and form micro fractures/cracks around the central steel bushing. There was no easy way I could tell without removing it.
The cam shaft seal was also leaking and it was getting progressively worse and I had also been planning on fitting a longer duration cam for a bit more top end pep so I made a decision to tackle all three jobs at once.
I had already obtained a NOS Fiat 4331512 camshaft from Italy. These where fitted to the 128 Rally Coupe and very early x1/9s. The duration is longer than the later camshafts with slightly more exhaust valve lift. The specs are:
4331512 = 24/68 64/28 with 9.35mm inlet lift and 9.30mm exhaust lift
Standard cam = 12/52 52/12 with 9.35mm inlet lift and 9.20mm exhaust lift
For the other parts I contacted the ever helpful Claire @ Eurosport-uk and added a steel camshaft wheel in addition to all the seals, gaskets, cam belt, tensioner etc that where required. I also intended to replace the auxiliary and camshaft seal but the latter proved to be an issue.
The first job was to check the valve clearances. Remove the air cleaner and box, throttle linkage, the cam cover and cam belt cover. Jack up the drivers side rear wheel, put the car in 4th gear and rotating the wheel forwards only rotate each lobe of the cam shaft so its pointing away from the valve. You may need to remove the oil that pools in the cambox with a Turkey Baster or similar. I didn't find any large clearances but two of the exhaust valves where on the tight side.
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| Getting started |
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| Rogue Hex head cam bolt, signs of previous work |
I had been advised to aim for 0.35mm inlet and 0.45mm exhaust but not go below 0.30 and 0.40mm
Next, I set the engine to TDC on Cylinder #4 and slackend off the camshaft nut and auxiliary shaft nut. Both are done up to 100fl-lb of torque! The camshaft nut loosened off with a breaker bar but the aux shaft nut wouldn't budge, first there was not enough room to get a breaker bar in and secondly the aux shaft wheel jumped the cam belt when I put a 17mm spanner on it and pulled hard!
At this point a little voice whispered in my ear this was going to be one of 'those' jobs!
I removed the cam belt and tensioner. Note: the tensioner stud secures a plate to the engine that covers the water jacket, when you remove the tensioner it's necessary to put a socket over the stud and tighten down again, if not coolant will slowly weep out all over the floor!
I used the old cam belt to wrap around the aux wheel and secured it off on an exhaust stud using some mole grips. Unfortunately the wheel still slipped on the belt. There is a special Fiat locking tool for the aux shaft wheel but getting one and fitting it in the tight space was not a viable option. I ended up refitting the tensioner and wrapping the belt around the wheel again and used the tensioner to provide....errr...extra tension on the belt. Now the belt didn't slip but I could not generate enough force to undo the nut! Arrrgh!
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| Cam belt wrapped and tied off with Mole grips |
I replaced the aux shaft seal, just remove the plate by undoing the three small bolts and taking care that you don't pull the aux shaft out whilst removing the plate just gently ease it off. If the shaft pulls out too far the fuel pump rod may fall off the cam on the shaft and you will need to remove the pump to refit it.
Tap the old seal out of the plate and fit a new one, clean the block around the aux shaft, fit a new gasket and re-fit the plate, done.
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| Aux Plate and pulley with my new super duper spanner |
Then I moved on to the camshaft itself. I inspected the resin camshaft wheel but couldn't note any cracks or major issues other than some wear on the teeth. Having bought a new all metal version I decided to fit it just incase, but first I had to fit the new camshaft.
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| Resin cam pulley |
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| Wear on teeth |
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| Old and new |
With the cambox on the bench remove each bucket and shim in turn noting what cylinder and what valve it belongs to, I used an old egg box (12 large eggs!) and placed the buckets and shims in the box labelling them as I went along.
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| Egg box! |
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| Cambox removed |
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| Old camshaft and cambox |
Cam shaft replacement is straight forward as well, remove the end plate and gasket and slide the camshaft out. I inspected the cam journals for scoring and perhaps should have measured them for wear but they looked fine so cleaned the box up and replaced the old shaft seal.
Next was to work out the required shims. The new cam has the same base circle of the old one and I was fairly confident that even with a new cambox to head gasket the clearance would come up in tolerance. I decided to replace all the shims with new ones and aim for 0.35mm inlet and 0.45mm exhaust. First you measure the existing shim and note the valve clearance taken previously. If the gap is too large by say 0.10mm it means the shim needs to be 0.10mm larger and conversely if the gap is too small by 0.1mm then the shim needs to be thinner by 0.10mm.
Shims are available from Eurosport-uk sized in 0.05mm steps from 2.7mm to 5.2mm, a wide range. With luck I managed to get all the gaps just about spot on except for one exhaust that ended up at 0.43mm. It’s important to not go below the minimum gap especially for the exhaust valves.
I installed the new camshaft in the box using engine assembly lube on the journals and the new seal, then fitted the end plate with a new gasket making sure the end plate did not touch the end of the camshaft.
After applying assembly lube to each cam lobe and valve bucket and shim I slid the buckets and shims into the cam box. I didn't use the penny magnets on reassembly as the assembly lube is thick enough to keep the buckets in place. Just be watchful though incase a bucket decides to make a bid for freedom as you turn the cam box over.
As the cambox was off and knowing BART had some previous head work prior to my purchase I re-torqued the head bolts. It is possible to do this with the cambox in place if you have the offset socket tool but I didn't so took the opportunity to do it now. I backed them off by 1/8 of a turn and torqued to the correct spec. The head bolts are not torque to yield types on BART.
Next I fitted a new cambox gasket and placed the cam box gently on top of the head. Before tightening down I made sure #4 cylinder was still at TDC and fitted the new camshaft pulley finger tightening the bolt. This allowed me to align the camshaft pulley timing mark to the engine snail mount. This is necessary as the 1300 engine is an interference fit and I didn't want the valves to come into contact with the pistons! I could have backed the engine off anti clockwise by 90 deg moving the pistons half way down the bore, that probably would have been better practice!
I then tightened down the cambox bolts in sequence a few turns each ensuring the cambox was secured evenly and torqued them to the correct spec.
I then refitted the old timing belt and wrapping it around the camshaft and a new auxiliary wheel in turn tightened both bolts with my new super duper aviation spanner.
Before fitting the new cam belt and tensioner I tried to remove the crank shaft nut. The idea was to replace the crankshaft seal as I already had everything apart. Would it move? No it wouldn't! No amount of heat or hammer gun persuasion would move it. As I had been at this for a number of days I decided it was a job for another time...after all it wasn't leaking...
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| Applying heat |
I fitted a new cam belt and tensioner, checked the cam timing and rotated the engine a few times before slackening the tensioner again and then retightening. A quick check of the valve clearances showed them to all be in spec. and where I wanted them to be.
I fitted a new cork cambox cover gasket (don't over tighten and crush it or it won't seal) and reassembled the rest of the engine but left the cam belt cover off so I could inspect and check everything. I retimed the car as the aux shaft had rotated a touch when fitting the new belt. BART fired up into life, yay! No leaks from the camshaft seal and most importantly no noise from the top of the engine, it sounded very smooth...but...the cam belt was now running in a different place than before and was worryingly running over the inside edge of the aux shaft pulley by a few mm.
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| Going back together |
What followed was way too many days of back and forth experiments, disassembly, reassembly and measurements of pulley wheel dimensions and combinations with old and new tensioners to determine what was the cause. Previously the belt had always rode on the outside edge of the camshaft pulley but it never overhung the edge. The combination of new pulleys and new camshaft shifted the belt to run on the inside of the wheels. I noted a 0.5mm offset on the new aux pulley I installed which was contributing to the overhang. In the end with another new belt and tensioner installed I came up with a compromise to use the new all metal camshaft pulley and the old aux shaft pulley. The belt now just rides on the edge of the aux shaft pulley with a slight overhang. It is something I'm going to keep an eye on, do a few miles and see if it settles down or requires more attention.
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Aux overhang with new pulley
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I've only put a few miles on BART since as another issue cropped up soon after I completed all of the above! More to follow....
Special thanks; I could not have done this without the valuable help and assistance forum SteveC 'fiatfactory' and the guys on the xweb forum, thank you!
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