Engine rebore question and clarification

Farmall Cub Forum -- Questions and answers to all of your Cub related issues.

Moderator: Team Cub

Forum rules
Notice: For sale and wanted posts are not allowed in this forum. Please use our free classifieds or one of our site sponsors for your tractor and parts needs.

Engine rebore question and clarification

Postby Jdbfish » Thu Dec 20, 2012 1:15 am

I have my engine at the machine shop now awaiting complete disassembly and measurement, along with a thorough vatte cleaning. Not sure if a rebore is needed or not. The engine was running fine with no smoke but one cylinder was only around 50 psi compression while the others were at 100 or so. I pulled the head and measured the cylinders at the top about an inch below the ring groove. All four measured 2.630 to 2.6315 and were round within .0015
Gss1007 pg28 states that a rebore is needed if taper exceeds .0105 and/or out of round exceeds .0025, which does not appear to be the case on initial inspection. If final dissasembly and inspection confirms this, can I just redone and replace the rings? If so, do I use standard size or 010 over and polish the ring gaps to get proper fit? Please give past experiences and results please. Thanks!,,
Jdbfish
Cub Star
Cub Star
 
Posts: 98
Joined: Mon Nov 12, 2012 9:52 pm
Zip Code: 76502

Re: Engine rebore question and clarification

Postby Gary Dotson » Thu Dec 20, 2012 6:52 am

While your taper & out of round may not be excessive, your cylinders have 5 - 6.5 thousands wear, that's a lot of piston skirt clearance. If that were my block and was at the machine going into the vat, it would also be going on the boring machine. Of course, have your machinist confirm your results and make his recommendation.
Gary Dotson
Team Cub Mentor
Team Cub Mentor
 
Posts: 2515
Joined: Thu Aug 03, 2006 6:20 am
Location: OH West Mansfield
Zip Code: 43358
Tractors Owned: 48 Cub Diesel (Cubota)
53 Cockshutt 20 restored (Shooter)
52 Cockshutt 20 unrestored
47 Leader "B" (Herckie)
49 Leader "D" (Princess)
49 Leader "D" very rough
48 Leader "D" unrestored
Kubota B6200E
Kubota B6200HST
Kubota B8200HST-D
Circle of Safety Award
Circle of Safety: Y

Re: Engine rebore question and clarification

Postby Boss Hog » Thu Dec 20, 2012 8:17 am

I think if you use .010 rings you will be too tight at the bottom of the cylinder, if you get the correct end gap at the top, I also think a rebore is needed
Boss
IN GOD WE TRUST
All others pay cash
Boss Hog
Power corrupts; absolute power corrupts absolutely byJohn Emerich Edward Dalberg

8th Va fest link viewtopic.php?f=8&t=81392&p=657790#p657790
User avatar
Boss Hog
Cub Pro
Cub Pro
 
Posts: 9658
Joined: Mon Oct 24, 2005 8:35 pm
Location: VA. Randolph
Zip Code: 23962
eBay ID: dmb2613
Circle of Safety Award
Circle of Safety: Y

Re: Engine rebore question and clarification

Postby JackF » Thu Dec 20, 2012 8:26 am

It's like Boss & Gary said that's a lot of piston skirt clearance. You’re probably didn’t hear the piston slap because of the steel pistons. Probably the low compression on the one cylinder is from a valve seat problem.

If you’re trying to get by cheap the machinist may be able to expand the piston skirts to compensate for the clearance.

If you reassemble with Aluminum pistons make sure you tell the machinist so he can add more clearance for the expansion. …… Most of all; have your machinist confirm your results and do his/her recommendation(s).
I’m really good at doing nothing…With that said…I’m really, really good at doing nothing
JackF
501 Club
501 Club
 
Posts: 904
Joined: Sat Feb 15, 2003 7:20 am
Zip Code: 00000

Re: Engine rebore question and clarification

Postby John *.?-!.* cub owner » Thu Dec 20, 2012 10:07 am

If you decide to rebore, I suggest getting the parts from the machine shop, and letting them reinstall and gap rings, etc.
"The Constitution is not an instrument for the government
to restrain the people, it is an instrument for the people to restrain the
government lest it come to dominate our lives and interests." Patrick Henry
User avatar
John *.?-!.* cub owner
Team Cub Guide
Team Cub Guide
 
Posts: 19100
Joined: Sun Feb 02, 2003 2:09 pm
Location: Mo, Potosi
Zip Code: 63664
Tractors Owned: 47, 48, 49 cub plus Wagner loader & other attachments. 41 Farmall H.

Re: Engine rebore question and clarification

Postby mrdibs » Thu Dec 20, 2012 12:25 pm

Mill the head too.
mrdibs
Cub Star
Cub Star
 
Posts: 99
Joined: Tue Feb 21, 2012 11:02 pm
Zip Code: 19520
Tractors Owned: 1948 Farmall Cub
2007 Cub Cadet


Return to Farmall Cub

Who is online

Users browsing this forum: Dale Finch, Eoghan, Posco, Stevo944 and 7 guests