Page 1 of 2 12 LastLast
Results 1 to 15 of 18
  1. #1
    Newbie
    Join Date
    Jun 2017
    Location
    Perth
    Posts
    20

    Default When to rebore an engine

    After a lot of reading here it seems that it is fairly common to rush off to the local machine shop for a re bore and deck.
    If an engine has no lip or visible damage to bores, after a 6 point measurement (3 top of cylinder, 3 bottom) what would be an acceptable difference in measurement just to re hone and re ring in a stock stroke street engine that only see's up to 5500 -6000 rpm. I understand that to be perfectly round is the key.
    cheers.

  2. #2
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,162

    Default

    not only round but the finish to seat rings is important. old worn bore may be glazed or to much clearance
    11 second E85 bottle fed boat anchor

  3. #3
    Do you ever leave?
    Join Date
    Oct 2008
    Location
    NZ
    Posts
    2,748

    Default

    Couple of thou would be about the max. A good machine shop can hone the bore back to round and parallel. Bearing in mind you will then have a couple of thou more clearance.

  4. #4
    Newbie
    Join Date
    Jun 2017
    Location
    Perth
    Posts
    20

    Default

    So the process would be strip and clean the block and off to the machine shop to measure and assess. If its +30 now and no visible damage then no doubt the recommendation may come back take to +40 and new pistons etc.
    cheers.

  5. #5
    Do you ever leave?
    Join Date
    Apr 2009
    Location
    NSW
    Posts
    5,192

    Default

    Are you intending to run cast or forged pistons?

  6. #6
    Newbie
    Join Date
    Jun 2017
    Location
    Perth
    Posts
    20

    Default

    Cast flat top pistons, standard stroke crank, A9L rods, oil mods to cam bearing 1 and 4, HQ heads 1.95/1.54 valves with pocket port and YT bolt on rockers. Rochester carb, maybe a performer manifold and spacer as car has A9X bonnet. Pretty mild engine just used for cruising on a Sunday. Not sure on cam yet. will replace the SBC in my Hatchback SS manual T10 with 2.70 9" rear end. Just an old school street car but want to put it back to 308 with original rocker covers etc.
    Any other suggestions are appreciated as I am by no means an expert but love the challenge of doing as much as I can on my car as its my pride and joy.
    Last edited by Brett0004; 17-01-2018 at 05:22 PM. Reason: addittions

  7. #7
    Do you ever leave?
    Join Date
    Jul 2009
    Location
    Childers Qld
    Posts
    4,031

    Default

    I was surprised to find that with a couple of clunkers that I have "built" over the years, were much better than I expected after ridge removal, a quick bottle brush hone & rering,,, the compression was pretty well exactly where it was when it was first built.... That particular engine was +0.060" already & lasted for quite a few years & I then sold that car & it was still good

  8. #8
    Newbie 71QPE's Avatar
    Join Date
    Aug 2017
    Location
    Marian
    Posts
    11

    Default

    If bores appears to be in good nick, out of round and piston to wall clearances are in tolerance i dont see a reason why you couldnt get away with a good hone and re ring. Would pay to check deck heights for sqaure too.


    Sent from my iPhone using Tapatalk

  9. #9
    Newbie 71QPE's Avatar
    Join Date
    Aug 2017
    Location
    Marian
    Posts
    11

    Default

    How many thou 00R are your bores? What piston to wall clearances have you got? You will have to measure all individual pistons and bores.


    Sent from my iPhone using Tapatalk

  10. #10
    Newbie
    Join Date
    Jun 2017
    Location
    Perth
    Posts
    20

    Default

    will measure and report back

  11. #11
    casual poster
    Join Date
    Jan 2012
    Location
    Melbourne
    Posts
    203

    Default

    These engines donít seem to mind poor tolerances. As long as thereís no ridge and clearances arenít ridiculously excessive they usually take to new rings quite well.

    Just make sure you use cast rings if the bores arenít perfect. They tend to seat better, but donít last quite as long as moly rings. Moly rings are more durable and better for sustained/frequent high rpm use.

    But realistically if you want to rev this thing to the moon youíd want to have it all machined properly anyway, so Iíd say cast rings would do just fine in your case.

  12. #12
    Newbie
    Join Date
    Jun 2017
    Location
    Perth
    Posts
    20

    Default

    Well I picked it up this afternoon (Gumtree special) and it looks to be ok in the bores. +30 dished pistons and standard rods. Got the December 76 short motor complete with a new engine stand and HX auto Rochester in good condition for $680 which I think was a fair deal. I can still see cross hatching in the bores as well as a little bit of shine, no ridge. I roughly measured a few of the bores with my digital vernier (will do after pull down with micrometer) and they all measured 40025 at 3 positions in a few cylinders. removed the sump and clean as. Bottom end has been overhauled as all rods have been numbered. Will start to pull it down tomorrow and report back.

  13. #13
    Newbie
    Join Date
    Jun 2017
    Location
    Perth
    Posts
    20

    Default

    Well I spent the day stripping the engine then cleaned down. All bearings looked serviceable just number 1 cam bearing had some scoring. the crank looked good and looked to have been ground with 10 thou over size mains. big end journals were unmarked.I started measuring the bores using telescoping gauge and micrometer. Using a 6 point measurement (3 top and 3 bottom of cylinders) the highest of all measurements was 1.6 thou for over size, 1.3 thou for out of round and 1.6 thou for taper with no visible scoring to bores I feel that I should be able to get away with just a hone. I will get a local machine shop to confirm. Now to knock out the cam bearings and go the oil mods as well as clean up all the casting dags in the block.

  14. #14
    Do you ever leave?
    Join Date
    Apr 2009
    Location
    NSW
    Posts
    5,192

    Default

    Quote Originally Posted by Brett0004 View Post
    Well I picked it up this afternoon (Gumtree special) and it looks to be ok in the bores. +30 dished pistons and standard rods. Got the December 76 short motor complete with a new engine stand and HX auto Rochester in good condition for $680 which I think was a fair deal. I can still see cross hatching in the bores as well as a little bit of shine, no ridge. I roughly measured a few of the bores with my digital vernier (will do after pull down with micrometer) and they all measured 40025 at 3 positions in a few cylinders. removed the sump and clean as. Bottom end has been overhauled as all rods have been numbered. Will start to pull it down tomorrow and report back.
    There is no "auto" HX Rochester unless it is an export engine (which used later HQ / early HJ carbs which have specific auto and manual carbs). HX Rochesters are the same for manual and auto, they all are after 12/74 in Australian engines.

    Engine sounds like it will be fine for a budget build. Just hone and fit new rings and bearings (bearings are cheap, whilst it is apart might as well fit them).

    Use a new cam too, not worth the hassle using an old one in a 308. New oil pump is almost a given too, or at least make sure the original is all within spec.

  15. #15
    Newbie
    Join Date
    Jun 2017
    Location
    Perth
    Posts
    20

    Default

    Quote Originally Posted by HK1837 View Post
    There is no "auto" HX Rochester unless it is an export engine (which used later HQ / early HJ carbs which have specific auto and manual carbs). HX Rochesters are the same for manual and auto, they all are after 12/74 in Australian engines.

    Engine sounds like it will be fine for a budget build. Just hone and fit new rings and bearings (bearings are cheap, whilst it is apart might as well fit them).

    Use a new cam too, not worth the hassle using an old one in a 308. New oil pump is almost a given too, or at least make sure the original is all within spec.
    Cheers HK1837. Yes was going to replace the items you mentioned. I tapped out the cam bearings today (spent most of the morning making the tool) and did the oiling mod to No 1 bearing and will tap and install the restrictor in No 4. Also cleaned up the internal casting dags.

Page 1 of 2 12 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Replies: 6
    Last Post: 23-12-2014, 10:07 PM
  2. 350 rebore.
    By GRUMPYQ in forum Chevrolet
    Replies: 1
    Last Post: 04-06-2012, 08:22 PM
  3. Gen 3/Ls1 Rebore??
    By hypass in forum Chevrolet
    Replies: 1
    Last Post: 21-08-2010, 02:56 PM
  4. Rebore or hone and rings
    By roadster in forum 6 & 4 Cylinder discussion
    Replies: 3
    Last Post: 24-07-2010, 02:55 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •