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08-30-2021, 09:54 AM | #1 |
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Another overbore question
A few years back I got the nicest 8BA block I have ever had. It had been stripped, baked, cleaned, mag & pressure tested. So, looking at building in the near future, currently it is 3 3/16 plus 0.60". Not looking to go to the max here, what should I take it out to? I'm thinking of Egge pistons and interested in the Metric Ring Packs that Gosfast (miss him) often spoke of.
Thanks fellas!
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08-30-2021, 11:50 AM | #2 |
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Re: Another overbore question
I know you can go to at least 3 5/16" (.125 over). I have done two so far, and the only problem I ran into was a small casting flaw in one cylinder of the second engine that showed up after the bore job. The machinist said because of it's position and size, we could just run with it, but I decided to sleeve that cylinder (for $85) just to be safe. Other than that, there was plenty of wall left and I have had no problems with either engine.
I know there are some here who have gone to 3 3/8" or even 3 7/16" (the max I have heard of was 3 7/16" +.030; that does scare me). Another reason I like 3 5/16" is that if you look hard enough, you can get the pistons for the same price as standard bore. (I like free cubic inches.) Going larger usually requires more expensive pistons. |
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08-30-2021, 02:37 PM | #3 |
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Re: Another overbore question
Consider a set of Egge .080 oversize pistons that would fit your desire to not go to the max. Or the next step would be 3-5/16 bore however there is the chance a pin hole flaw will be found its not unusual for that to happen.
Ronnieroadster
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08-30-2021, 04:18 PM | #4 |
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Re: Another overbore question
Over boring a flathead block is dicey, as the cylinder wall thickness varies due to the core shift in casting. In my racing days, we went through lots of blocks to get a maximum increase without breaching a wall. Back then, the junk yards were full of engines. Today the supply of blocks can be very expensive. In one case, we finally had one we could bore
without hitting a sand hole. Our joy was shattered when our car popped a wall when we started it on the trailer at the track! |
08-30-2021, 06:33 PM | #5 |
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Re: Another overbore question
Had the 59L bored out 3 & 5/16, and pressure tested before assembly. Found a very tiny weep hole in 1 cylinder. Bored & sleeved it, and all is well. Got the NOS sleeve from Fred at South Side, and Hans at Advance Engines sleeved it on his RMC boring mill. which bores off the center line vs the deck.
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08-31-2021, 12:09 PM | #6 |
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Re: Another overbore question
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08-31-2021, 07:24 PM | #7 |
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Re: Another overbore question
Ron,
Thanks for weighing in on my discussion. You and I have conversed on topics before and your wisdom is always appreciated. I completely agree that good blocks are getting harder to find. I mentioned in my OP that I have this excellent 8BA block that is already 3 3/16 +.060. Ronnieroadster suggested I go with Egge .080 pistons, as I wish to minimally overbore. I'm inclined to go this way, and intend to use 3 rings. Have you ever used Mahle or Wisco pistons, what are your thoughts on brands of rings? Thanks so much. Shoebox
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08-31-2021, 10:36 PM | #8 | |
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Re: Another overbore question
Quote:
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09-01-2021, 06:30 AM | #9 |
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Re: Another overbore question
I've not used Mahle or Wisco pistons . . . though would have no problem giving either of them a try. You might check with them all for pricing and delivery - can be a real issue these days.
What I would recommend is picking a bore size that allows you to use a modern ring pack -- like 1.5, 1.5, 3.0 mm rings - with a good moly top ring. When I order my custom pistons from Ross, I only use modern rings - sometimes with a custom bore size that matches the typical metric ring sizes (usually on 1/2 mm boundaries). |
09-01-2021, 12:05 PM | #10 |
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Re: Another overbore question
No, I'm not familiar with that brand of piston. I use only OEM or Egge pistons. However, depending on the style of piston, the piston to cylinder wall to skirt clearance is critical. For street use a steel strut piston is best as it can be set up the tightest at . 0015/.002. The only 296 engine i ever built has a set of no/name steel strut pistons in it and it's still running after 15 years of use and never used a drop of oil. It was recently replaced with a 294 blown engine. Nice to have a spare engine. good luck.
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09-01-2021, 03:32 PM | #11 | |
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Re: Another overbore question
Quote:
The Wisco auto pistons seemed very high tech. Short skirts, various coatings, etc. In the end, I went with Ross and a Total Seal metric ring packs for a number of reasons. Like you said, once you start getting into custom sizes, metric modern rings may be the only option. |
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09-03-2021, 12:56 PM | #12 | |
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Re: Another overbore question
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Tim, As a Kawasaki dealer years ago is where I got my familiarity with Wiseco pistons too. The more I dig into this I believe Ross pistons are in my future. On their website yesterday I saw for flatheads, one part# 80582 which uses conventional ring set, and another larger piston using metric rings. I sent them a message about metric ring availability with the 3.187 size piston but haven't heard back yet. How big did you go with your engine?
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09-03-2021, 01:08 PM | #13 | |
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Re: Another overbore question
Quote:
RonnieRoadster (poster above) built the motor and he knows his stuff when it comes to Ross pistons I would give Ross a call and talk to their tech team. Ross do have "in stock" items. but they can do anything you want, you just have to ask them. My pistons had to be custom made and the turn around was approx. 3 weeks. Good luck with the build and keep asking questions. Last edited by Tim Ayers; 09-03-2021 at 01:25 PM. |
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09-03-2021, 03:33 PM | #14 |
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Re: Another overbore question
The engine was run several times before loading it on the trailer. We start it and let it run at a fast idle. The cylinder wall broke after about 20 minutes. I am long past my racing days, but we run a large machine shop in Iowa, where we do lots of reboring and other work, mostly from other shops. Most of the flatheads come from hobbyists and smaller shops. My own '47 convertible got the whole treatment, and has been faultless for the 25 years I have owned it. My age (86) means it is time to sell it so someone else can enjoy!
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09-03-2021, 05:28 PM | #15 |
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Re: Another overbore question
To the original poster: The availability of +.083 pistons should give you a good solution to your question. These were commonly used for replacements when sleeves were removed. If you have problems finding these contact me as I am sure I still have a few sets of these heavy old slugs.
The rush to tout the use of thinner, "metric" rings is another silly, poorly informed, myth as it relates to a common "cruiser" vehicle. Under the normal driving circumstance the best that can be said is quicker break in/wear in is typical. The negative side is less use/mileage before wear takes a toll while there is no measurable improvement in any characteristic important to daily driving. |
09-03-2021, 05:35 PM | #16 | |
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Re: Another overbore question
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Thanks Tony |
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09-03-2021, 06:50 PM | #17 |
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Re: Another overbore question
Okay
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09-03-2021, 09:06 PM | #18 |
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Re: Another overbore question
Ross pistons for street use is a poor choice, as they require a larger piston to wall clearance. Best piston is a tight piston.
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