Camshaft & Rocker Gear Repairs - 2016
Ever since I've had 1070 the rocker gear has always been a little noisy. Valve clearance adjustments never made much of a difference and recently the noise has become more pronounced, so time to do something. Apart from regular servicing and a few cosmetic changes I've never done anything mechanical to the engine in my ten years of ownership so we are delving into virgin territory here!
Note. What we did here is not to the original factory specification but is just a description of what was done. It is not recommended for any other Aprilia engine.
First a description from "Servicing An Aprilia" (don't forget there is no factory service manual)
In cast-iron box (38-2551) bolted to head. Driven by endless inverted tooth chain and located by fork (38-2517) bolted to front end of box engaging in groove in front bearing.
Chain wheel (38-2513) spigoted and bolted to end of camshaft and drilled for vernier timing, with loose dowel (38-2583).
Spring-loaded jockey sprocket behind cover in front of block casting maintains chain tension. For renewal of timing chain engine must be removed and crankshaft dropped. (not applicable for this operation)
When removing head take chain wheel off camshaft, first marking timing with dab of paint, and without disengaging chain allow it to drop where it will rest on jockey sprocket, so the head can be lifted off .
Hollow shaft (38-2566) above camshaft carries four plain (38-2555) and four cranked rockers (38-2564). Two interchangeable pair of auxiliary rockers on shafts (38-2568) carried at each side on three pillars (38-2560/62) bear at inner ends on plain rockers and outer ends on two outer valves. Cranked rockers operate two pairs of inner valves, by short push-rods (38-2534) in guides in box.
All four valves inclined to off side are inlet, those inclined to near side exhaust. Adjustment by grub screw and lock-nut on ends of rockers.
The first task was to remove the ignition wires and plug connectors before taking off the rocker cover. Next the two outer auxiliary rockers and then the shaft on top of the camshaft carrier with the rocker shafts and finally the camshaft carrier.
A close inspection of the rockers revealed some wear on all the faces, some more than others, which was most likely the source of the engine noise. Back in 1991 when the engine was rebuilt the rockers were metal sprayed and ground and a new camshaft, made at a cost of £519.75, was fitted.
The camshaft shows signs of uneven wear and a poorly ground surface, but the engine has done around 40-50K km since the restoration.
On the recommendation of a few Lancia owners I took the camshaft and rocker arms to Clive Cams in Ferntree Gully to have them reground. Supplied with factory drawings and diagrams I was hopeful that they would come back close to spec and in a reasonable time! I was out of action for a few weeks after a bit of surgery and short hospital stay, but it still took six weeks for the work to be completed. The camshaft did come back beautifully finished with a protective phosphor coating and to what is probably an improved specification, considering I had given them a non-standard one to work with. The only difficulty they had was the cranked type rocker arms (38-2553) didn't fit on their grinding machine.
To grind the cranked rockers I followed Marc Bondini's method. Mounting a spare rocker arm shaft accurately in the mill/drill vice and a grinding disc in the chuck, by lightly holding the end of the rocker arm and slowly lowering the spindle to follow the profile I got a good result that only needed to be finished with a diamond stone.
Next was to set the camshaft up. I'm now in an area of zero knowledge so time to call on the experts and got Mike D. over to have a look. The first problem we spot is that Clive Cams have written the cam Lift @ Lobe 0.325" (8.26mm), we think this cannot be right.
Mounting the cam between centres on the lathe for accuracy with the dial gauge we get a measurement of 0.274" (7mm), more like it. Next we calculated the lobe centres, i.e. the angle between the inlet and exhaust lobes. The factory spec is 110°, we measured this cam at 108°. Mike explained that this will give a little more top end power and that 110° was quite conservative anyway.
Clive gave me the advertised timing for this cam as exhaust 70/30, inlet 30/70, with a duration of approx. 280°. In simple terms the the exhaust opens 70° after bottom dead centre and closes 30° after top dead centre and the inlet valves open 30° before TDC and close 70° after TDC. We decided to follow this as it would potentially help the engine breath better, it gave an overlap of 60° (see my timing diagram below). The factory standard is a little hard to establish but according to the 2nd series manual the exhaust valves open 40° before BDC, close 2° after TDC and inlet valves open 2° before TDC and close 45° after BDC. The factory timing diagram is slightly complicated and confusing!
Next problem to solve was how to measure the 30° before TDC to set the valve timing on the inlet valve. If the engine is out of the car a timing disc could be mounted on the crankshaft, but here the engine was still in the car. With a bit of head scratching we came up with a plan to mount the camshaft in it's carrier box, clamp it onto the bed of the mill/drill, fit the timing disc to the front of the cam and use a dial gauge to calculate the lift on a inlet lobe at 30°BTDC. This we did and came up with a measurement of 0.024" lift.
Now the following has nothing to do with the Lancia factory settings or method and is here for information only. Mike is a Morgan man who has raced Lotus 7, Austin Healey Sprites etc., so as far as he is concerned number one cylinder is at the front like any other conventional 4 cyl engine, there were a few mumblings about over engineered Italian %#*@#!
Armed with all this we fitted the camshaft and rocker gear on the engine, after getting absolute TDC on no.1 (the front left cyl, it was one tooth off on the flywheel) and setting the valve timing using our measurements with a valve clearance of 0.008" (the spec for this camshaft). First try and she refused to start and only spat back through the carburettor. Moving the ignition wires around made no difference! So off came the rocker cover to recheck the timing, oops we set it on an exhaust lobe! Re-set on the inlet lobe, fitted the ignition wires onto their correct plugs and she fired up. PROBLEM!, very low oil pressure, yikes!
Off with the rocker cover again. The Welch plug at the back end of the camshaft had come out! My fault as it was removed for the regrind and I didn't refit it carefully. I turned up a new one out of aluminium to a nice tight interference fit. A double check of all the Re8 carrier bolts torqued to the 22 lb./ft recommended in the LMC Hints & Tips booklet, the rocker cover back on again, success!
Following Clive's notes we'd lubricated the cam with Penrite Camshaft & Engine Assembly Lube and ran the engine at the recommended 2000 rpm for 20 mins to bed things in and prevent any scuffing of the nicely reground parts. The first test run and all the previous "tappet" noise has gone, she seemed to pull better from 60 km/h in top, the engine exhaust note has a little more of a bark and the engine ran a little warmer, a good thing as it has always run a little cool. A longer run with a properly sealed rocker cover & plug connectors and she's very quiet, smoother and pulls up hills with more go. Time and a lot more kilometres will tell how successful this has all been.
Camshaft specification summary.
Now we get to the complicated bit.
Before I'd sent the cam off I measured the lobe height at 30.36mm, the factory spec is 29.66mm. I suspect when the engine was done in 1991 they had a cam turned up from a billet and only got it close, in fact I've no idea what they did apart from charge a lot of money for it. The diameter of the lobes were 23.46mm giving a lift @ lobe of 6.9mm, factory spec is 6.16mm.
Parts returned from Clive Cams
Measuring the lobe lift = 0.274" (7mm)
Assembled rocker arms & camshaft.
Check the rocker faces line up with cam by fitting spacers.
New aluminium Welch plug!
Factory camshaft lobe.
As described by Mike:
As the valve timing is advertised as 30/70 inlet and 70/30 exhaust we took measurements of the cam by placing the cam in the cam housing from the motor and fitting a degree wheel.
First measurement was valve lift to reference back to after installation. The second measurement was to find the peak of the cam lobe on both inlet and exhaust which then allowed us to calculate the degrees between the lobe centres. With this info. we could map the specs against the original cam specs to make sure the cam would suit the engine.eg close lobe centre line will increase overlap and low speed driving can deteriorate.
Next task was to work backwards from the inlet centre line to TDC point and then back to the advertised point of 30 degrees before TDC and then to the start of lift. The term advertised is used as the cam starts to activate the valve train earlier than this as it has a lift section often referred to as ramps that take up valve clearance and smooths out the start of valve acceleration but give false readings when a dial indicator is installed. On this particular cam the dial indicator showed a reading of .024 inches lift between the start of lift and TDC .
The camshaft when installed therefore is correct when the engine is on TDC and the cam is turned to give .024 inches lift on inlet valve. Cam manufacturers generally offer valve timing at .050 inches or inlet lift at TDC when these specs are not included then the above method is used. Lift at TDC is the best for in vehicle set up when a degree wheel cannot be fitted as it only requires a dial indicator to set the timing.
Measuring lift on cam at 30° = 0.024" (0.61m)
The Lancia spec is set with a valve clearance of 0.5mm. With the clearances set to 0.25mm there is around an extra 2 degrees on each opening and closing, see numbers in brackets.
The new valve timing is non standard and not necessarily recommended. At the time of writing the engine's performance does however appear to be improved.