I have been reading in a few manuals that the maximum bore for the 6 cylinder engine is +0.030.
***For example the workshop manual for XK 150 reads "Oversizes available +5, +10, +15, +20 and +0.030.
***Jaguar E Type Owners Workshop Manual; "Maximum rebore size +0.30 in (0.76 mm)
I have read many topics here as to boring/honing blocks to +040, +060 over and our vendors sell pistons +0.030, +0.040, +0.060. (Why not +0.050??) Apparently, bores over +0.030 are normal today and apparently are not problematic.
Is there a document from Jaguar stating itâs OK? Or is this something thatâŚjust happened? Curious as to just how this came about.
Back story; I have a block that has been bored out to +0.040 and at the time I was unsure if this is OK and the block is usable.
Regards
Tim
My experience is mostly with the six cylinder engine from the Standard era through the end of the Mark V. In those engines, I run a 70 thousandths-over cylinder bore with no issues. I have the impression the typical oversizes âallowedâ were influenced by what parts supply chain could readily be supported. My 70 thou-over use custom pistons. I donât know if anyone has ever done heat and mechanical structure analysis for oversize limits. And practical experience depending on application (racing, road use, etc) might have insights.
One issue regarding boring 3.8âs and 4.2âs past the Jag published limit is that theyâre factory sleeved so Iâd guess Jag didnât want you to compromise the integrity of the sleeve. Plus â7x blockâ 4.2âs have 2 horizontal slots between the bores connecting the Left and Right sides of the water jackets that are only sealed by the sleeve - another reason to keep the sleeve material as thick as possible.
People have often bored 3.4 engines to 3.8 without failure. If itâs a numbers matching car I wouldnât recommend it. Momo and Cunningham were known for that but not the first. Itâs +.157 But that may have been before honing to final size to match the pistons.
I ones quite inadvertently found out how far you can take a Datsun 1200 engine: I had obtained a set of high compression Datsun competition pistons for it, and I neglected to actually measure the pistons I just took the machine shop the box.
They bored it awrightyâŚAnd then it became a Datsun 1500!
Thank you all for the reply. Good info. I would still like to know:
Why not 0.050" over pistons?
Where/how/when did the decision get made to go over the factory MAX of 0.030"? I think we will never know; )
On the plus side no one stated DO NOT GO OVER FACTORY! So my 0.040 over bored block is just fine.
My 120 came to me with itâs number matching 3.4 block bored to 3.8. It need boring again, so I had it sonic checked, and it was judged to have âenough meatâ, so we added 0.020" to that. Runs fine.