A few questions if you guys don’t mind!
 

My 69 1bbl engine that I did a valve job on last year is back out of the car. I pulled the head last year due to a bad oil leak and we decided to send the head out in case it was warped and since it was the machine shop we gave it a valve job, valve seals etc. Like a dummy I didn’t send out the block since the bores looked decent and the rod and main bearings looked good.

It ran ok last summer but could never get a smooth idle and the first tank of gas came in at 11 mpg. Did a compression test and had three of six cylinders weak (110 versus 145 on the other three).

We opened up the engine again and discovered that it was already thirty over but the ring gap was way too high because the bore was too big for the pistons. Long story short it needs to go 40 over but I can only find 60 over pistons. My machinist doesn’t suggest 60 over due to overheating risks.

So my plan is to instead use a virgin 68 block I have and punch it 30 and use the 30 over pistons from the 69 engine (machinist said they are in perfect shape.

So what do you guys think? I disassembled the 68 engine and it’s in great virgin shape (it could get away with 10 thousand but figured might as well go 30 and save buying pistons. Both blocks have excellent cranks that can use standard rod and main bearings again.

Being a 68 block I will have to drill the bypass hole on the front to use the 69 water pump without external bypass provision.

I learned something else about the original engine I didn’t notice before. While the head is original the cam (and likely the cam housing) is from a 67 (based on the cam casting number). Which is why the car probably still had the thermostat housing spacer (with the bypass fitting plugged with a bolt). The cam is in good shape but the cam from the spare (68) engine is super nice so I’m going to use that one since it’s nicer and the correct 68-69 cam.

Second question, how do you install a thermostat without that spacer when there is no inset groove to seat the thermostat on neither the thermostat housing or cam housing?? The inset groove is in the spacer with the bypass fitting. I figured that they must have changed the design of either the cam or thermostat housing to seat the thermostat but to my surprise the part numbers for both housings are unchanged for 66-69. What gives?

Third thing is that the spare engine had a mesh oil screen inserted in the fill tube (protruding down into the sump. I’ve never seen this before and both my OHC don’t have them. Now I know why both my cars always sweat oil from the filler cap! I’ll buy some similar looking mesh and make one for my other (the Sprint) car.

You won’t run into any overheating issues on a OHC going .060” overbore. That is only a concern for the V8s.
All the OHC 6s had the mesh at the bottom of the fill tube to prevent oil from being slung up the pipe.
Hopefully your valve height is within spec after the valve job. If not, that could be part of your low compression issue. (Valve not sealing)
If you want to discuss further, IM me and I will give you my phone number.
Thanks,
Rob
Woodland Motorsports LLC

As Rob mentioned .060 is not an issue. My 1st Cammer was bored to .060 and I ran that one for years.

Have you checked with EGGE on Pistons?

As far as the Cam Tower not having the relief for a Thermostat, That would be a first for me. If this is the case either a swap or possibly having it machined?

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copper brillo pads have been used as a screen
just make sure its really copper thats well made
and doesnt have any loose fodder

I suspect that Sprintbird is on the right track, the valves might not be sealing well. 11 MPG is ghastly, perhaps the cam is slightly outa time from milling the head as well?? If the ring gap is a tad generous, I would hit it with the dingleballs & re ring it!

Overbore overheating on a stock rebuild is a myth all the way around from people boring out their engines while also adding high compression heads, big cam, etc a bunch of stuff that adds heat but nothing for the cooling side.

Race Tech / Auto Tech will make you a good reasonable priced better than factory piston of any bore size you ask. Factory valve reliefs and all.

Thanks all! I’ll rebuild the original engine at 60 over. We pulled the fill pipe on my second spare engine and it also still had the mesh so I’m good for both my OHC cars.

Really happy about discovering this because both my cars always sweat oil out the fill cap and you get those whiffs of burning oil at red lights. Hopefully this will cure that problem.

I’m going to run the Cam and housing from my 68spare engine since both the cam and cam housing uses the same on for 68-69. That cam is in beautiful shape and the one that was on the car was the incorrect 67 cam anyhow. I wonder what the difference was?

What do you guys do to tension the timing belt, shop manual shows a tool that looks like a variation on a Burrows gauge, the factory timing specification for the one barrel engine was 0° advance, but this car seem to like 9 to 12° in terms of getting the best possible idle and vacuum levels. However, with three cylinders at such low compression levels, it would make sense that it would absorb more timing to better burn the fuel that was not being sufficiently compressed.

We did have a good look at the head and the valve job looks beautiful. Nothing seems to be mechanically wrong, but will do it careful of the valve geometry once we reassemble the engine after machine work in the block.

I guess you know that 69 cam timing is different than 66-8?
Ive gone by feel on belt tension,midpoint of longest span you cant quite turn belt 90*.

I didn’t know about the change in cam timing? What did they change?

Just follow the timing procedure in your '69 service manual.
The '69 TDC mark on the Cam Sprocket was relocated to the bottom of the sprocket. '66-'68 is on top.

As far as belt tension, no "special" tool is needed. I do all mine by hand.

I'm not sure about '69 but the front cover backing plate on the '66-'67 has lines used to set tension. (See Left side)

As long as the deflection falls within these lines you're good to go.
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Disregard the factory timing specs with today's gas most of us are running at 10/13 BTDC on timing and it makes a world of difference.

Cheers.

Thanks again, funny how the OHC seems to want more timing with todays crappy gas while the V8 needs less than factory specs.

As for my 11 mpg it was a bit shocking. My Catalina ragtop with 428 and AC average in the 12 range around town and 14 plus on the highway. My other Cat with the 2 bbl 400 and no AC is 14-15 around town.

I don’t know the mileage on my Sprint because the odo cut out a few years ago but the speedo works fine.

I’d think a 1bbl OHC with auto trans (3.23 in back) should be in the 16-18 range around town?

Your around town mileage is hurt by the ST300. (And possible lack of valve sealing/tuning) I would think it would be better than 11 MPG, but I do not know how you drive it. The first gear of that trans is too tall, and really works that 1bbl hard. I usually recommend either a TH350 and keep your gear or 200 4R with 3.90s or 4.33s with a OHC 6.

I drive very relaxed, lots of short trips though since it was new to me. We will see in the spring how it responds to good compression on all cylinders. The carb is a correct coded NOS unit that we went through with fresh seals. I’d say I’m pretty confident that I had the carb and distributor in an excellent state of tune. Transmission seems to function well with no sign of slippage but only two gears obviously hampers performance and economy.