I’m getting ready to replace the valve stem seals on a 98 Mazda Protege 1.5L Z5 engine. I was reading through and comparing the directions from 2 manuals (Haynes and Mazda’s Work Shop Manual) and came across the camshaft cap bolt tightening sequences. I have to say I’m a bit confused because the loosening sequences are identical in these 2 manuals but the tightening sequences aren’t even close. Is there more than one right way to tighten these bolts? I would normally just ignore the Haynes and follow the Mazda manual but the Haynes has some credibility since it’s loosening sequence matches the Mazda manual’s loosening sequence. I don’t know what to do. Heck, I don’t even understand the importance of this bolt tightening order since the two camshafts appear to be independent of each other. Does anybody understand this? If you do, please fill me in. Thank you
I would follow the procedure in the Mazda manual. The bolt tightening sequence is VERY important. If you were to tighten the bolts from side to side then the camshaft may seize and destroy the cam bearings and possibly the camshaft. This might be time to ask a knowledgeable friend to help you or let a good mechanic tighten and torque the bolts for you.
The cam tightening sequence is based on the loading of the cam lobes against the valve springs. It is necessary to snug the caps adjacent to the loaded lobes first and move outward. If that makes no sense to you follow the instructions to the Nth degree.
If the bolts were tightened incorrectly and the camshaft was going to seize and destroy the cam bearings and possibly the camshaft, would it be obvious the second the engine was started? Or could it be silent and gradually get worse with miles? I ask because I recently changed out a couple intake valve adjuster discs and didn’t follow the tightening and loosening order (actually had no idea there was such a thing at the time) The engine sounds fine though. Did I get Lucky?
Improper tightening may result in immediate failure or possibly damage that doesn’t show up for many miles or no damage at all. Time will tell.
According to my VW (different brand but OHC as well) Bentley manual, the reason for removing and installing the cam bearing caps as specified is to prevent the cam from tilting in a tight bearing which could damage a bearing or else could bend the camshaft.
Possibly there is more than one way to accomplish this so all of the instructions that you have may be correct.
VW Removal: Remove cam bearing caps 5,1 and 3 in that order. Then simultaneously and gradually remove bearing caps 2 and 4.
VW Installation: Simultaneously and gradually tighten 2 and 4 bearing cap nuts. Then install 5 and 3, then 1 in that order.
It might be possible that after 2 and 4 are installed, the installation of 1,3 and 5 is not critical.
“Possibly there is more than one way to accomplish this so all of the instructions that you have may be correct.”
Exactly what I was thinking, at first, but strayed away from that theory because the procedures and sequences are so different. The Haynes says to tighten one bolt per cap at a time and then one bolt on the next cap and so on. The Mazda manual has it so that you tighten both bolts on each cap before moving to next cap. Very different. Not only one bolt per cap at a time versus both bolts together but a completely different sequence as well. And the Mazda manual doesn’t say whether to start with the inside or outside cap bolt. Hopefully because it doesn’t matter. But if it doesn’t matter why would the Haynes have you starting with the inside bolts. This thing is going to drive me crazy. I guess I’ll combine the two sets of directions and follow the Mazda cap sequence but tighten the inside bolts first as the Haynes says to do.
As Rod Knox said, loading is the important part. Carefully read the manuals specifically where they talk about the “time” for each cam in relation to the crankshaft. They may give different scenarios, which will explain why they then have differing tightening sequences.
Of course, the Haynes one may be just plain wrong. Given my druthers, I’d use the Mazda manual.
VW by the way, has individual cam bearing caps. If your Mazda is similar, ok. If your bearing caps are all tied together as an assembly then an additional concern would be the possibility of bending the assembly.
You want the camshaft to be pushed down into its saddles evenly, so the cam is not tilted or mis-aligned as you tighten the bolts…If one of the sequences available to you is the opposite of the loosening sequence, use that one…You move from bolt to bolt, tightening each one a few turns and moving on to the next, keeping the pressure even between them, pulling the cam down evenly…
I would not do a few turns at a time. One turn is more gradual and easy to count.