Installing a non thrust plate cam into a thrust plate block

[Mopud]

Hi guys,

I have trawled this info for a while and I'm getting lost in a mess of about 30 different open tabs on the topic. I would really appreciate some feedback from someone with experience in relation to the following.

I have a 2001 model 4.0 block which I'm installing the comp cams 68-231-4 cam into. I understand now (after trying to install today) that my block uses the thrust plate design as chrysler changed to after i think 1997. Previously they used a bolt, washer, pin and spring design to keep the camshaft in place.

From what i've learnt through researching these forums and other sources on the web, if i purchase the 83502890 bolt kit: Cam Bolt, Pin & Spring from a dealer or hesco etc i'll be able to install the camshaft into my block. What i haven't been able to work out is compatibility with the timing cover. My understanding of it is the timing cover needs a guide or some sort of nipple to keep the spring/pin in place but my timing cover does not have that, only a recess. I read in this thread http://www.jeepstrokers.com/forum/viewtopic.php?t=737 that some have the 'little bump' and some reportedly don't. I'm here to report that mine does not

I have seen this post http://www.jeepstrokers.com/forum/viewt ... +COVER+MOD but would find it easier if i could just install a new timing cover that would work. I have an older timing cover off a donor 258 motor from a j10 and its seems to have a guide of sorts on it for this purpose but the bolt holes appear to be slightly different (a similar pattern but some extras). The older timing cover does not have a provision for the timing chain snubber either http://www.4wd.com/productdetails.aspx? ... rtID=51516.

I already have the earlier cam bolt and washer from the donor 258 engine and I have the compcams roller timing chain and sprocket set to suit this cam.

What do I need to do to get this cam installed correctly?

Some pics are attached for reference.

Regards and thanks in advance,

Mopud

[Bodo]

I'd advise you to use whatever timing cover matches your brackets. I used a 99 WJ timing cover on my 96 XJ. They are ALMOST the same, but some of the accessory bolts didn't quite work out.

I've seen engines with the button that have had timing covers with and without the little nipple.

[SilverXJ]

You will need a timing cover with that dimple.. or do the modification to the cover with out it. That dimple is where the pin rides on.

[Bodo]

You will need a timing cover with that dimple

Hmm, is it really THAT important? All that the button does it keep a little pressure on the cam to keep it from smacking the timing cover. I can't see that the little pressure lost from the nipple not being there being a make or break kind of thing. Besides, isn't the timing chain already keeping everything lined up?
I can see a wear issue being a possibility, but not critical.

[Mopud]

You will need a timing cover with that dimple.. or do the modification to the cover with out it. That dimple is where the pin rides on.

I was afraid of this, I wanted to avoid the mod if i could and a new timing cover with that dimple to suit my block would be near impossible to find.

I would have reused the spring and pin off the donor 258 but it looks like when the previous owner rebuilt it, he didn't even use it. That explains i think why the timing cover has been scored by the head of the camshaft bolt. it might even explain why one of the cam lobes was ground almost completely down to nothing and he suffered a bent pushrod!

I did note this written in my comp cams installation booklet. If this is the case, perhaps the dimple isn't as important as we might think? I still believe the pin and spring set up is still required though.

Step 7: Install the new crankshaft sprocket on the snout of the crank. It is recommended to use a
Crankshaft Timing Sprocket Installation Tool (Part #4933) for all applications that have an
interference fit crank sprocket. If the new camshaft being installed is a hydraulic or solid roller lifter
cam, now is the time to check camshaft endplay. For instructions on how to do so, see “Checking
Camshaft Endplay” section in this booklet. If the new camshaft being installed is a hydraulic or solid
flat tappet cam, this step is not necessary. Flat tappet cams have taper ground into their lobes, which
pushes the cam into the proper position and holds it there while the engine is running. Checking
endplay is also unnecessary in engines equipped with cam retaining plates, whether the cam used is a
flat tappet or roller.

[SilverXJ]

Hmm, is it really THAT important?

I don't know if it is that important. It might make the cover a bit stronger in that spot plus more metal to wear.

I did note this written in my comp cams installation booklet. If this is the case, perhaps the dimple isn't as important as we might think? I still believe the pin and spring set up is still required though.

If the new camshaft being installed is a hydraulic or solid
flat tappet cam, this step is not necessary. Flat tappet cams have taper ground into their lobes, which
pushes the cam into the proper position and holds it there while the engine is running.

That is technically true, the lobes have a taper which pulls the cam into the block as well as the oil pump drive. However, some 4.2Ls didn't have the pin. It was added later in life. Also, I have rear an AERA document that mentions a knocking sound coming from the block and that bolt, spring and pin are necessary to keep the cam against the block and eliminate the knocking sound.

CAMSHAFT THRUST CONTROL

Camshaft Thrust Control On
Chrysler 2.5, 4.0 & 4.2L (Jeep) Engines

AERA membership has reported a mysterious knocking noise on Chrysler 2.5, 4.0 and 4.2L engines used in various Jeep utility vehicles. The noise is loudest at the lower front area of the engine and has, on occasion, been reported in all of the above listed engines. The noise will disappear if the engine is operated at higher than idle speed.

Disassembly of the engine revealed that the camshaft gear was making contact with the timing cover. Recalling the engine's assembly, several machinists remembered encountering a bolt that had an 1/8 hole in it. Most were unsure where to install the bolt.

As of the 1991 production year, Chrysler has updated the engine to a new method of retaining the camshaft in the block. Prior model year engines were equipped with a camshaft thrust plate. This has been superseded by a special bolt, spring, plunger and front cover (see illustration). The plunger assembly maintains constant pressure on the camshaft, preventing it from moving
forward. Camshaft chucking will result if this thrust control assembly is not reinstalled. The pin rests against a small protruding pad in the front cover that is reported to be 1.000 from the gasket mounting surface.

A replacement Pin Package is available from Chrysler under the Part #83502890.

The AERA Technical Committee

[Mopud]

I found that article also but I can't find it on AERA's site to see the illustration. I will call the dealer to see if they have the pin/spring part in stock. I'll also see if they have any matching timing covers with the dimple. Provided they don't want me to re-mortgage my house i might go with that before I mod my existing cover.

I guess if i get hold of that spring set up i'd be able to see for myself what will work and what won't as far as fixing a dimple to the cover. Are there any other tried and trusted methods/materials I can use aside from using the hilok aircraft fastener that dwg86 used?

[SilverXJ]

I don't see why you couldn't use something else. It obviously doesn't have to be hardened as the aluminum is fairly soft to begin with. Rivet? some small bolt?

[IH 392]

I have rear an AERA document that mentions a knocking sound coming from the block and that bolt, spring and pin are necessary to keep the cam against the block and eliminate the knocking sound.

CAMSHAFT THRUST CONTROL

Camshaft Thrust Control On
Chrysler 2.5, 4.0 & 4.2L (Jeep) Engines

AERA membership has reported a mysterious knocking noise on Chrysler 2.5, 4.0 and 4.2L engines used in various Jeep utility vehicles. The noise is loudest at the lower front area of the engine and has, on occasion, been reported in all of the above listed engines. The noise will disappear if the engine is operated at higher than idle speed.

Disassembly of the engine revealed that the camshaft gear was making contact with the timing cover. Recalling the engine's assembly, several machinists remembered encountering a bolt that had an 1/8 hole in it. Most were unsure where to install the bolt.

As of the 1991 production year, Chrysler has updated the engine to a new method of retaining the camshaft in the block. Prior model year engines were equipped with a camshaft thrust plate. This has been superseded by a special bolt, spring, plunger and front cover (see illustration). The plunger assembly maintains constant pressure on the camshaft, preventing it from moving
forward. Camshaft chucking will result if this thrust control assembly is not reinstalled. The pin rests against a small protruding pad in the front cover that is reported to be 1.000 from the gasket mounting surface.

A replacement Pin Package is available from Chrysler under the Part #83502890.

The AERA Technical Committee

I wondered why they did that?, none of the 199's, 232's or 258's Ive been into had the button or the thrust plate they speak of??? IIRC

[SilverXJ]

The thrust plate didn't come until 99 or so IIRC. It is a better way to retain the cam, but it also changes the snout design so you can't use the earlier cam.. and there aren't ' any after market cams to fit that.

[Mopud]

I don't see why you couldn't use something else. It obviously doesn't have to be hardened as the aluminum is fairly soft to begin with. Rivet? some small bolt?

I guess it doesn't really matter, as long as it helps keep the spring in place and seals well it can be anything. As soon as I get the pin and spring i'll have a look and see what I can knock up.

The thrust plate didn't come until 99 or so IIRC. It is a better way to retain the cam, but it also changes the snout design so you can't use the earlier cam.. and there aren't ' any after market cams to fit that.

Yeah it's a pain they don't offer the different configs or specify this info when you purchase. If i'd have known the differences at the time I could have been better prepared. I guess this stuff comes down to experience.
This is why many cam manufacturers state their aftermarket cams supports only up to 1997 because after that they changed to the thrust plate design. (I can confirm 1998 model Jeep GC used the thrust plate as I checked the service manual). I'd like to see what a 96 or 97 wrangler have as technically they should use the same cast timing cover to suit the block design as the later model Wranglers but should use the pin and spring style retention method. At least definitely for the 1996. I'll see if i can solve this with the dealership.

Cheers

Mopud

[lafrad]

My '99 timing cover had a button on the inside of the timing cover to support the old style cam pin, but the block came setup (and used) the newer style thrust plate on the block.

Putting the after-market cam pin it was easy... worked great.


The '99 XJ is a little weird... New style intake manifold, but still a distributor. seems like the engine is a bit frankenstein'd together...

[unlimitedrubicon]

One benefit of having the button that has not been mentioned yet is the extra space away from the timing cover would help to properly preload the spring. I am not sure how much of a difference it would be with button vs. no button, but how many tolerances in a well-built engine can be off by a few thousandths and still be acceptable?

[Mopud]

One benefit of having the button that has not been mentioned yet is the extra space away from the timing cover would help to properly preload the spring. I am not sure how much of a difference it would be with button vs. no button, but how many tolerances in a well-built engine can be off by a few thousandths and still be acceptable?

I see your point but I don't honestly think the dimple is adding space to the pin/spring, it's just acting as a locator to stop it from walking. As long as it is applying pressure to the camshaft the difference won't really matter.

I've got the part 83502890 bolt kit: Cam Bolt, Pin & Spring coming from a Jeep engines place in the Eastern States (Australia - I'm in the West) who is fedexing it from the USA for me. Jeep Australia wanted a 3 week lead time for it.. I can't wait that long. I'll just have to mod the timing cover but will stop by a jeep wrecker just around the corner to see if he has anything.

[SilverXJ]

I see your point but I don't honestly think the dimple is adding space to the pin/spring, it's just acting as a locator to stop it from walking. As long as it is applying pressure to the camshaft the difference won't really matter.

Actually I think that dimple might be needed. It will preload the spring more and it actually sticks in the recess in the bolt if the cam moves forward enough. If it isn't there there could be a chance that the bolt makes contact with the cover. A solution would be a) use a stiffer spring, b) use a longer pin to preload the spring more, c) skip the spring, use a longer rod and set the end play manually. C is a pain in the ass thought as you have to take the cover on and off with the gasket in place to get the correct end play while adjusting the pin length.