Jump to content
HybridZ

Cam tower query-- When to line bore?


Daeron

Recommended Posts

My brothers are building an engine for their ITS car, and Chris (the elder) asked me to mine HybridZ and "talk to some of my engine buddies" to find an answer regarding (you guessed it) line boring the cam towers. They obviously want to avoid boring it if possible, but are more than willing to have it done if needs be.

 

I searched about for a thread or two I can recall coming up in recent months, but I think the boring questions were asked in a thread that had a title about something else.

 

The cam apparently spins freely, feels great... except for a single spot in the rotation. This is what he told me: "If you spin the cam with a bit of force, it continues for a rotation or two, but there is a rough spot. You can feel the rough spot, and after a rotation or two the rough spot halts the spin."

 

In other words, it spins wonderfully freely, but it has one rough spot. It can be spun beyond that spot.. and through my search I see a "two fingers" rule for spinning the cam; if two fingers can spin it, it is good. I do not know how much force it takes to get beyond that spot, but I imagine not much.

 

Is this irregularity itself enough to call for a line bore? Is it a matter of how much resistance the irregularity presents??

 

I am continuing my search through the evening, because I am fairly certain I can find my answer.... but I figured I would submit the question as plain as day, because this is an answer that should be more readily available through the search engine.

Link to comment
Share on other sites

  • Administrators

Keep in mind, when these cam towers were originally bored, they were bored while attached to a “true flat” head. So be sure the head you are working with is “true and flat” on both the bottom chamber side AND top deck surface! If the head is warped, the entire head warps and just surfacing the bottom leaves the top bowed and the cam line through the cam towers is follow that bow! Align boring cam towers to correct that situation is ludicrous as the towers will now be oval and too large on the tops and bottoms of the offending towers.

 

Generally, if the cam can be spun by hand, even if it is a little sticky, the oil wedge developed around the circumference of the cam journal while the engine is running is sufficient and journal/tower wear will be negligible to nil.

 

Cam tower to cam journal clearance is pretty forgiving.

Here are a few ways to deal with slight sticky spot while spinning the cam by hand.

 

Having one spot during each cam rotation that sticks is usually indicative of a bent cam AND out of round cam tower/s or a nick on the camshaft journal and or tower bore. if a nick is found, carefully dress the high spot of nick and then buff the journals of the cam with scotch-brite by hand, and be sure to wash/flush the cam thoroughly afterward. Same goes for the towers.

 

Another approach.

With the cam tower bolts just loose, i.e. a little tighter than finger tight, rap on the top of the towers lightly with a soft faced hammer, (rubber faced will work, but a hard plastic is preferred), then torque cam tower bolts back to spec.

 

Another approach is with the cam towers all tight, using that hard plastic mallet, lightly tap the individual towers fore and aft, while rotating the cam by hand. You’ll feel the cam get tighter and/or looser as you do this. I said tap "LIGHTLY!" That will usually free up a slight sticky spot while rotating the cam as you are “setting” the cam towers while tapping.

 

If a head was dropped upside down on the cam tower/s, the cam tower is most likely oval. Don’t bother align boring as the cam tower will still have an oval tower. Also, regardless of how many times you align hone it, it'll still be too large. :lmao:

 

Last resort. Just replace the cam towers as a set. The new cam towers should be stamped as to their position before they are removed from the donor head and reinstalled in that same position. I have a few sets of matched stamped cam towers, (I’ll need to verify if they are for the internal or external cam oiling). External cam oiling towers can be used with internaly oiled cams. You can use the spray bar or plug the oil ports for the spray bar.

 

 

Hope that helps.

Paul

Link to comment
Share on other sites

So, if a fellow takes a stock head that has never been removed, then removes it and it is not true, you should not line bore?

I had a line bore done on a honda engine, wow that turned nicely. The also milled the towers to match, due to the lager hole.

 

Now remembering back long ago, some one told me that a seasoned block that had its twist that got line bored to true its cylinders is better than even new.

 

If the deck is flat from surfacing and the bore is not true, would it not be prudent to realign bore to given seasoned head?

 

BTW sicking it out there cause I want to understand and I know who I'm talking to:), so be gentle.

Link to comment
Share on other sites

I ditto BRAAP's comments.

He hits the reasons for the binding issue.

The only times I have seen L-Cam Towers line-bored was after someone heliarced them to repair a galled saddle and needed to line the repaired tower up with the others in the set (curiously they used a VW Line Boring Apparatus, modified, to do this!) The reason for the repair was they didn't have another set of towers to use as a set. When using a mismatched set of towers I've seen them lined to fit. When using the cast-iron towers (L4's) when installing bronze cam bushings.

 

The point being, as BRAAP said, if there is a reason for the binding, fix the reason---line boring the tower will only mask the root cause.

 

Surfacing the bottom of the head, but not the top is a BIG cause for this kind of bind. A head with a 0.008" warp resurfaced on the bottom only can have no oil wedge at all in one of the towers towards one edge, and just be skirting disaster on the edge of a bearing living on oil spilloff...then you get a burp in oil pressure or suck some foam in a corner and the oil wedge drops minimally, the edge of the cam bearing runs on bare aluminum long enough to 'grab' and then either the cam snaps, and you get a galled tower...or something else lets go. Sure, it turned fine... I'd look for top surface warpage or see if the head was surfaced properly. That would be my first suspicion especially if the head was returned from the surfacing shop with tight cam towers (mine come back in a box, usually!)

Link to comment
Share on other sites

  • Administrators
…

I had a line bore done on a honda engine, wow that turned nicely. The also milled the towers to match, due to the lager hole.

 

BTW sicking it out there cause I want to understand and I know who I'm talking to:), so be gentle.

 

 

Woldson,

(Donning the kid gloves…) Not knowing the Honda head you are referring to, I am going to assume the cam line was machined in to the head, i.e. it did not have “removable” cam towers. In that instance, with the cam line machined into the head itself, with a warped head, one method to truing the cam line is to align bore/hone the cam line. In that case, I recommend performing some form of heating/bending-straightening procedure to true the head as much possible first, then bore/hone the cam line. Again that procedure applies to heads with the cam line integral with the head.

 

 

Woldson,

FWIW. I have been building engines much longer than Paul (BRAAP), and I have never had issues with any advice he has given.

Phred

 

Thank you for the compliment Phred. That means a lot to me coming you. shy.gif

Link to comment
Share on other sites

In case you hadn't realized yet, Cobra Tim there is one of my two brothers who own this ITS car :)

 

Thanks for the advice. The other brother (Chris is his name, and I am Shawn, for the record.) has since explained to me that this "slight rough spot" was felt with the head off of the engine, and he has read these responses and decided that on this particular head, his concern was a red herring. We DO have plenty of heads from which to pull towers, so if we need to replace them come assembly time, we will.

Link to comment
Share on other sites

Yes, Woldson the Honda engines cam towers are no different than main bearing caps on any other engine...you mill the ends of the caps down to make an undersized oval hole., then you line bore from there.

 

Different than the L-Engine, which doesn't have a split-bearing setup on the cam bores.

 

And of course, making sure an aluminum head is straight BEFORE line-boring a split bore makes perfect sense (see comments on RB Head Salvage in another post of mine to someoneorother...) LOL

Link to comment
Share on other sites

Yes, Woldson the Honda engines cam towers are no different than main bearing caps on any other engine...you mill the ends of the caps down to make an undersized oval hole., then you line bore from there.

 

Different than the L-Engine, which doesn't have a split-bearing setup on the cam bores.

 

And of course, making sure an aluminum head is straight BEFORE line-boring a split bore makes perfect sense (see comments on RB Head Salvage in another post of mine to someoneorother...) LOL

 

Crap I was remebering the honda head thinking it was similar to the z head!!

 

Sorry to all big fat duh mistake on my part! Thing is I have not worked on a honda in 7 years, yet recently pulled apart that turbo engine few months ago.

 

Gheezz must be getting old. Sorry again.

 

Our towers are complete, not split (mumbling to my self.....idiot)

Link to comment
Share on other sites

If this is a maximum effort ITS nissan engine, you will certainly be taking a bit off the head to bring the chambers down to as small as allowed by the rules or you will end up a moving chicane for all the sunbelt, B.C. Gerolomy, and Rebello drivers.

 

Knowing that, you will most likely be using head saver shims anyway so machining the face that meets the rocker pivots and cam towers shouldn't hurt if it turns out you have warpage of the entire head.

 

Talk the guys here since you will be racing them and meeting them anyway.

 

http://www.improvedtouring.com/forums/index.php

 

Make sure to check your options such that you can view posts that are older than 30 days old or you won't find what you are looking for.

Link to comment
Share on other sites

If this is a maximum effort ITS nissan engine, you will certainly be taking a bit off the head to bring the chambers down to as small as allowed by the rules or you will end up a moving chicane for all the sunbelt, B.C. Gerolomy, and Rebello drivers.

 

Knowing that, you will most likely be using head saver shims anyway so machining the face that meets the rocker pivots and cam towers shouldn't hurt if it turns out you have warpage of the entire head.

 

Talk the guys here since you will be racing them and meeting them anyway.

 

http://www.improvedtouring.com/forums/index.php

 

Make sure to check your options such that you can view posts that are older than 30 days old or you won't find what you are looking for.

 

This won’t be our full tilt race motor... Right now we're working on a good mule... looking to be about mid pack. My brother Chris post quite frequently on ITforums and we've met a few of the Datsun guys from up north.

Link to comment
Share on other sites

Knowing that, you will most likely be using head saver shims anyway so machining the face that meets the rocker pivots and cam towers shouldn't hurt if it turns out you have warpage of the entire head.

 

Talk the guys here since you will be racing them and meeting them anyway.

 

http://www.improvedtouring.com/forums/index.php

 

Make sure to check your options such that you can view posts that are older than 30 days old or you won't find what you are looking for.

 

Don't believe head saver shims would be legal, but until you win something nobody would care if you had a 3 liter. Remember you're allowed .025 total off the head thickness for shaving, starting at 4.248". That doesn't mean, however, that you can just go whack .025 off the bottom, because if you did that on an E31 or early E88 you'd end up past the 9.5:1 comp ratio you're allowed. But again, for a mule, who's looking. Just keep that in mind for when you're ready to win the ARRC.

 

Definitely start hanging around the Datsun forum at improvedtouring.com.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...