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Cheap 1275 rebuild

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TulsaFred

TulsaFred

Jedi Warrior
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OK, so this will be anathema to Hap and the other high quality engine builders out there, but here goes.

My goal, for a number of reasons, is to do my own 1275 rebuild (no real experience) on a shoestring budget. It will be a mild street engine for my bugeye. The engine came from a guy who was selling a 74 midget and had this motor as a spare sitting in his shed since the mid-1980s. It appears to have relatively modest wear.

I took it to a machine shop and they recommeded turning the crank .010, boring the cylinders .030 (I think, maybe .020), putting in hardened seats, etc. This came to an estimate in the thousands.

I inspected and measured the engine as best I could with a digital caliper. These somewhat imprecise measurements were all within .005 in from spec. The crank journals all look perfect. There is a minimal ridge on the cylinders but I couldn't really catch it with a fingernail.

So I thought about it and decided to hot tank and magnaflux the block/head/rods, new cam bearings, and put in new valve guides. About $275 as I recall.

I took it home and honed the cylinders with a 3-stone hone on a drill and tried to get a reasonable cross hatch. I decarbonized the pistons, combustion chamber, and valves using a wire wheel and bead blaster. I lapped the valves and put on new valve springs. New rings (STD), bearings (STD), oil pump, lifters, timing chain, oil pressure relief valve and valve seals. A few hundred dollars all told.

I'm bolting it back up like this. I'll need to rebuild the carbs.

My plan is to put it in and see how it runs. If it sounds funny, runs bad, smokes etc. I'll pull it back out and have a pro redo it right. I'll only be out less than a grand and have gained a lot of experience and knowledge in the process.

I am able to find all kinds of advice on precise and specific detailed tolerances, necessary machine work, etc for a "proper" engine rebuild. However, I also know that there are a lot of engines with lots of miles that still run pretty good despite getting out of spec over 50-100K miles. It's hard to find information on a shade tree mechanics budget rebuild without a lot of machine work.

So what do you guys think? Will the motor be crap, or will it surprise us with how cheaply a rebuild can be done for street purposes?

Fred
 
Cheep rebuilds were a way of life not to many years ago. Think 60s and 70s in my case. I use to do it yearly with my daily driver 948.
 
Jack,
If you did yearly budget rebuilds or refreshes, what has been your experience? What kinds of problems remained or occurred after that type of work? Did the motor do a lot better after?

Fred
 
I would not say a lot better but it did keep up with the big folks on the way to work. Hehe.

I would come home from work about 4, pull engine, rebuild, stuff back in and drive to work in the morning. No time for anything fancy. Also had a stock long block ready to go just in case, but it was unmodified so hated to think of useing it.

Never, over 30 years had any major problems to worry about. Yep, did run it like I stole it, every day. Ran a BE for almost 29 years to work.

Unless you have a specific prob your budget rebuild should be good for quite a few miles.
 
TulsaFred said:
It's hard to find information on a shade tree mechanics budget rebuild without a lot of machine work.

Will the motor be crap, or will it surprise us with how cheaply a rebuild can be done for street purposes?

Fred
Click to expand...

Brother, you've come to the right place! Yeah, it'll be crap but you'll be surprised if you put it together right. You should have used a bead hone, but oh well. Supposedly those things can ruin cylinders.

My crank was/is shot. It was/is in dire need of turning. One journal ate some of the hardened lifter face that flaked off. It looked like one of the dual offest ground GM 3.8 V6 journals. It had a ridge so sharp and high it cut my finger like a razor blade. To top it off it was .002 out of round on all the rod journals. I did a LIGHT* polish and hone. New rings, rods, thrust and main bearings. The head was done by the P.O. I expected to get 10K MAX out of this engine but it's still going strong @ 13K. I plan to look at the bottom end and put a TR6 oil pump in (1500). Oh, yeah, I run the crap out of it regularly.

*Light polish: worked all the ridge out but with the lightest possible paper. The idea is to smooth it out. You don't want to take any more material off than nessisary. I built this motor out in the open under a filthy pole shed. I think Hap would have passed out if he had seen the shape of this engine and the environment it was assembled in. That being said, all parts were SUPER CLEAN durring assembly. If the crank passes the penny test leave it be. Did you mark your lifters to their proper bore/lobe? If not replace ALL of them.

BTW, I've got $500 in my "rebuild" and that including tools like the crank socket and bead hone, ring compressor etc... Make sure your oil pump is in spec or change it.

One thing I have always done is build oil pressure before I let it light off. I use Lucas oil treatment too in this engine. I find it helps slow oil drainback from a worn motor. It sticks better to prevent dry starts too.

People always ask me how much oil pressure I have. I don't know nor do I want to.

This is just my recipe ( maybe for disaster), YMMV.
 
Insert's and rings are a standard. Won't go as long as a rebore but might go half as long.

Kurt.
 
Kellysguy what is the penny test?

Kurt what do you mean by inserts? If you mean cylinder liners, don't you have to bore the block and press them in? That seems as expensive as regular boring.

BTW I never disassembled my rocker shaft assembly. It "looks" ok :wink:. What should I look out for and check before/during assembly.

Fred
 
A three-stone hone is for straight cylinders. You wanna use a ball hone to break the glaze of used cylinders. But no matter now. Get her running and drive it.

I did a similar refresh after I bought mine. Runs great and no more blowing oil out the rear. I have a spare engine that I may rebuild, but not now.

I don't see a water pump on your list. This is not an option IMO. You got the engine out and apart. Unless the WP is not very old replace it.
 
Fred: In these parts, (the home of cheeeep!!), we call new bearings, 'bearing inserts'. So if an engine is'nt too far gone and has to come out for say a clutch job its common to stick in 'rings and inserts'.

Kurt.
 
Fred: Here is my procedure. 1: Crank and pistons out. Clean block with solvent. I use the old bearing shells to cover the oil holes so that nothing gets in them in the cleaning process.(turn them around so they cover the oil holes).
2: find a tin can that will cover the bottom of the cylinder bores and use a ball end hone for deglazing ( put tape on the shaft so that you can see to not go too deep. Have engine inverted on the engine stand.)( I'm trying to keep all grinding grit out of the crankcase).
Once the cylinder's are deglazed and given a nice cross hatch pattern,clean and reassemble. Always check clearances with plastigage. (new oil pump is a good investment.)
Always keep track of which lifter's go on which cam lobes. If you lose track replace lifter's with new and maybe cam if it shows some wear.
When cleaning the grit out of the cylinders after deglazing I use gasoline then hot soap and water till a clean rag wiped in the bore comes out clean. Making sure no grit is left in the engine can't be emphasised enough.
Thats how I've done it, others may vary!

Kurt.
 
Fred: Forgot about the head and unless you have the tools I think I would send that out. If the rocker shaft does'nt have a obvious groove where the rockers run or much play in the rockers its probably not worth worrying about. If needed a new rocker shaft will help alot and not set you back much.

Kurt.
 
Nothing wrong with a "cheap" rebuild. Cleanliness and attention to detail is the same without regard to the cost of a rebuild.

I've built a number of "Driver School" engines with this kind of formula. I use the factory sleeved blocks since they can't bore +40. Good cleaning, hone the bores with a flex-hone, new rings, bearings, an autocross cam, new lifters, competition valve job (multi-angle) on the head, a little porting, cut the head 0.020" shooting for about 9.25 to 1 and inspect the rockershaft and polish the rocker pads. Runs all day and good for many years. About 6500 rpm. Great to learn on. A little engine helps the budding racer learn to drive the car rather than use the right foot only and wuss-out in the corners.

Two things to watch out for that haven't been directly mentioned yet. 1)Worn out top ring groove/land (> 0.006") clearance between new ring and groove face. When you get into the 8-10 thou range, there is a likeliehood that the top ring is going to break into pieces rather soon after the rebuild. Then things get worse with continued operation. The ring starts breaking into smaller pieces and the ring groove widens even more. I've seen top ring grooves over 3/16" wide. 2) Worn out lifters/tappets. The stock stuff can look pretty bad sometimes. The face of the lifter might look like someone took a pickaxe to it and there are many chipped out holes in the face. These are absolutely unusable. Replace any that have chipped or worn faces.

On the rocker shaft, sometimes, I have rolled the rocker shaft 180 degrees and redrilled the grub screw hole. Puts the worn/grooved part opposite the normal pivot point. Just make sure to clean out the center of the shaft. There may be a threaded cleanout plug on one of the shaft ends.

Good luck on your rebuild,
Mike Miller
 
Mike,
Can you please expand on the top ring groove clearence? Do you mean the difference between the thickness of the top ring and the groove or the distance between the back of the ring and the bottem of the groove? Can both of these be addressed by proper ring size in both thickness and diameter in a .040 over engine?
Thanks, Rut
 
Rut:

Good question. The clearance I'm talking about is the difference between the thickness of the ring and top or bottom inside face of the ring groove. What I usually do is clean the ring groove with a groove cleaning tool. Then install a new ring in the groove. Using a feeler gauge, select 0.004" thick blade and insert it between the ring and the groove top/bottom face. Keep working your way up or down in thickness until finding the one that has a little "drag" on the blade. Then work your way around the ring groove to detect any distortion in the ring groove itself on the piston or a bent ring.

On race engines using aftermarket pistons, it is common to run into rings that won't fit from a "Depth" perspective like you mention in the second part of your second question. Most ring manufacturers recommend the ring be at least 0.003" below the outside of the piston. Otherwise the ring can expand and bind between the piston and the cylinder wall.

For the last question, The first part is "sometimes". If the ring grooves are worn and the piston absolutely has to be reused, the ring groove can be machined for a slightly thicker ring. Usually, the pistons get replaced. The answer to the second part is most of time, a suitable ring package can be found to address the ring fitup in the groove. I work with Hastings a good bit on finding USA sourced ring packages for EU made after market pistons and I often have to specify the ring groove sizes to make sure a particular ring will work.

Hope this gives you the answer to your questions.
Mike
 
Thanks for the good info guys.

This kind of stuff is very useful, because it requires experience. It is easy to find professional rebuilding advice with required clearances and criteria for cylinder boring and such.
What is harder to find is what will actually happen if you bend the rules a little.

My suspicion is that building a perfect engine is required for racing, competition use, and professional shops, but that a less than perfect (ie. a little too much cylinder taper or out of round, a little too much bearing clearance, not placing hardened valve seats, etc.) may still run quite well for an occasionally driven street engine. How much is a little and how much will lead to a smoking, oil burning engine is the key and I've talked to very knowledgeable machinists who know the specs but can't answer these gray area questions. We'll see.

BTW, I also wonder about the wisdom of replacing certain components given the poor quality of so many reproduction parts, and lack of availability of factory parts.

For example, should I replace my original oil pump when it seems fine and the engine has few miles. While this SEEMS prudent and is inexpensive, I am very concerned that a moderately used original that has proven itself in-service may be much better than a cheap Chinese or India made reproduction.

Based on my experience, the risk of the repro being faulty, incorrectly machined, poor fitting, etc. seems much higher than the risk of reusing a factory part that seems "ok". Some simple advice on how to evaluate these original parts would be very helpful.

Fred
 
Mike,
Thanks for the detailed reply and I don't want to hijack this thread, but the info on the thickness of the rings is good to know. I currently have a 948, bored .040 over to 2.52 and it came with Jahns domed pistons (with a broken top ring). Everything else is standard and I would like to reuse the pistons. Where would I source rings to fit the piston and engine? The gap between the top ring and the ring groove is .035" or 10 times what it should be. The pistons measure 2.511 at the bottem of the skirt and 2.510 at the top. Thoughts?
Thanbks, Rut
 
I'll "come clean". Not too long ago I pulled apart the 1275 engine that is in my midget. I knew it had a blown head gasket between 2&3, and I thought there were broken rings in #1. Turns out all the cylinders are pretty oval shape. The valve guides where extremely worn and there was significant valve recession into head.

I didn't want to do a full rebuild, I just wanted the car back on the road for occasional drives until I can start work on my FI/turbo motor. So I put in new bearings and bolted on a used aluminum head that I bought cheap some years ago.

The engine is low on compression, but doesn't use much oil. It is a real slow poke, but I trust it will get me there eventually.

That was some 800 miles ago.
 
Rut:

I'll bet those Jahn's use the original stock 0.071" thick rings. Measure the thickness of your rings and see what they are. If you need some odds and ends rings, let me know. I have a couple shelves full of partial ring sets from business acquisitions, donations and my 35+ years of racing. I've even got some of the old Jahn's pistons myself. There are some old Austins that used a 5/64's ring in a bore size close to that. If the ring groove isn't badly worn, then I can help you get what you need from a local supplier or directly from Hastings.

TulsaFred:

Check the Oil pump for wear by inserting a feeler gauge between the outer ring and the aluminum case. 0.008" or less and its okay. 9-10 caution, 10+ it needs replacement. Also inspect the peaks of the rotor lobe (center piece) for grooves and scratches. Big gouges and such will let oil leak by and not build pressure. Small shallow scratches are okay. Pack oil pump with a light grease/STP/vaseline to help with initial oil pickup. Coat the oil relief plunger with same to make sure it doesn't stick. Put a 1/4" lock washer under the relief cap to push a little more on the spring and help insure the relief valve is closed at operation.

Take care guys. Been doing engines for 35+ years in these things. Built everything from a $50 rebuild using only new rings to a $10K dry-sumped 16/1 948 screamer for the SCCA National Championships. Cleaniness is the most important engine building tool. Next, if it doesn't "feel right", it probably isn't going to last. You can tell a lot about the build of an engine by the way the parts fit up and how each part tightens, torques, rotates, slides or feels. If you don't feel comfortable with something find out why.

Thanks,
Mike Miller
Comptune
 
Thanks MIke.
And don't underestimate the value of your experience. We need all the old hands to post as much of this type of thing as possible.
I'm 48, and there are few guys my age and younger with this knowledge. If it doesn't get imparted by the more experienced, it will become a lost art.
How many younger guys know how to rebuild an SU carb or tear down an A-series motor? Not many.

Keep the tips coming!
Fred
 
Mike,
Looked at the pistons and measured 1 and they look pretty good. Very sharp edges in the ring grooves and clean. The measurements are:
Top ring groove .090
2nd ring groove .090
Oil ring groove .151

Rings removed from pistons:
Top ring .061
2nd ring .061
Oil ring .123

This 948 came dissasembled and in a box and the PO said it had a 'seized bearing', but the bearings and journals look really good. Several of the rings still on the pistons are broken, but look new otherwise. The're .040 over and the gap while in the bore looks excessive. I would like to buy .060 over rings and file to fit or get the proper rings in the first place. Like Fred, I'd like to do an economy rebuild.
Thanks, Rut
 
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