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MG MGB GT V8 Factory Originals Technical - Preload
I am currently replacing my head gaskets and I am concerned about the preload of the tappets/lifters on my Rover 3.5 .
If I remember correctly when I built this engine 8 years ago I torqued the rocker shafts to 30-35 lbs and that was it. The car has run fine to this point.
Because the tappets are hydraulic would that not take care of any adjustment issue’s or preload?
Thanks for the help
Are you replacing like for like in respect of the gaskets, if so then dimensions inside the engine will be the same so nothing to worry about.
Not a bad idea to spin the engine over with the plugs out as this will help everything to settle back to where it was and with the cap off the radiator help to expel any trapped air.
Once engine is running and warmed up, check again for airlocks and top up with coolant as necessary, it does help to have the front of the car raised.
Thanks for the information. All good advise.
What I am doing is replacing the head gaskets with identical type head gaskets.
I have heard about preloading the lifters as done by shimming the rocker shafts and because I have hydraulic lifters I am wondering why it is done and how it is done
|Yes, Check the preload of the lifters to be safe. Hydraulic lifters will pump up to the nearest point of pressure to absorb any wear. But, the preload is anticipating that the cam lobes, lifter faces, pushrod ends and rocker tips will wear, and they do. I think the total compression of a lifter is like 0.060" so split the difference, 0.030"cold. As the motor heats up, that expansion will cause the the lifter to move the other direction. Hence, the 0.030" the other direction. With no preload, the engine will wear and then the ticking starts since things are sloppy.|
See link for a nice explanation. It's VW based but the same applies to any flat, hydraulic lifter.
As you can see from the link to the VW site it is not difficult to write an article about this subject.
The important issues are is the engine in good condition and what mileage has it covered and has the oil been changed at regular periods, say every 6000 miles or less.
The other important factor re lifters is has the engine been modified in any way such as new after market cam which can have a different base circle which affects preload. A camshaft in a Rover/Buick engine that has done more than 70.000 miles will be fairly worn and not unusual to find some lobes very badly worn in whch case replacement of cam and lifters together with timing gear becomes necessary.
Basically if the engine is standard and in good condition then you have no need to worry about setting the preload as it should be within the 20-60thou. limits and only if the preload was in excess of 60thou. would you need to fit shims under the rocker shaft pillars to reduce it to the correct figure.
Measuring and setting preload is a sod of a job, took me a bout 2 hours to do mine on a highly modified engine which has virtually no atandard parts.
If you do decide to to check and adjust preload remember that the rocker ration of 1.6/1 must be applied to the thickness of any shims installed. as a 10 thou shim will reduce preload by 16 thou, at the lifter.
Exactly the information I was looking for.
I will defiantly check out the preload as I put the rockers back on the heads.
Can't hurt and will give me piece of mind.
|I read about this often and checked my standard factory V8 when fitting new cam and tappets. A figure of 20-60 thou was being bandied about and is quoted on the RPI site. I was a bit taken aback to find mine were 110-120 on the right and 40-110 on the left. Spoke to Clive Wheatley and the MGOC and their opinion is that unless the engine is highly modified there shouldn't be a problem as the whole purpose of hydraulic tappets is to cope with a wide tolerance in the rest of the valve gear. Spoke to someone at RPI, who despite what is written on their site said "you wouldn't want to go as low as 20 thou and 120 thou should be fine".|
How are you measuring? My new set of Crower lifters only have a total of 0.063" of travel.
|I find that a little odd as all the manufacturers seem to recommend the 20 - 60 thou. figures.|
Are you sure about that figure for the Crowers as most hydraulic lifters seem to go solid at 4mm. or approx 160 thou.
|Check page 7 of this pdf file:|
|SJS I can't be sure how I measured it, I presume I put the new lifters in dry then measured the clearance with the cam off the lobe and the lifter fully depressed, but that's a guess.|
I can't speak for my old cam other than to say no lobes looked obviously bigger or smaller than the others. But all of the tappets with a straight edge across the cam surface showed barely any light coming underneath, and they had done around 65k.
|I stand corrected. My old lifters that came out of the 215 must have had 0.063" travel but they probably were loaded with oil and were not compressible. The new lifters have just over 0.160" travel right out of the box. |
Ironic that the nice info packet on the link was not included in the cam or lifter set. All I got was a small sheet mentioning that 0.020 to 0.060 preload is needed and how to use adjustable pushrods.
Wayne, Good info on the cam prelube. I have ZDDplus going in but didn't know about the SD,SE single viscosity needs for break-in.
|AS I mentioned before these lifters have been in the engine for a few years now. |
As I read all the information above, it appears I will be unable to get an accurate reading as the are full of oil and thus not compressible!
So, since they have not given me any trouble in all these years I am just going to put them back in and torque them up to 25 lbs.
Not exactly true. Even though they are oil-filled, they will bleed down when the engine is not running. You can measure the preload with a spark plug feeler gauge (wire type, looks like ells). Just put the wire under the lifter retaining wire ring and on top of the lifter seat/plunger. Which ever one fits, that's your lifter compression.
I still haven't put the valley pan back in so will give her a shot.
This thread was discussed between 08/03/2009 and 15/03/2009
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