1725 Re-build.

[Mike O'D]

The WSM for the 1725 engine lists the various bore and piston grades. As an example, grade A bores have a diameter of 3.2102 - 3.2106. Grade A pistons have a diameter of 3.2096 - 3.2092. Tightest combination would give a difference of .001" and loosest would give .0014". This seems impossibly tight. Am I missing something?

Thanks.

Mike

 

[husky drvr]

Mike,

Actually, WSM145 lists piston skirt clearance as .0006/.0014 in. with the stock cast aluminum tin plated piston (WSM145 - General Data - pg. 17 - "Piston").

The grading system was used as an assembly aid to allow choosing a graded piston to be fitted to a graded cylinder instead of having to have the machine shop bore each cylinder to fit a specific piston.

The good news is if you are rebuilding your engine with new O/S pistons, the grading system is irrelevant. You should follow the piston manufacturer's recommendation about skirt clearance. Also, the machine shop should have the new pistons in hand before setting up to bore the block. Cast pistons don't expand as much as forged pistons.

HTH

 

[Mike O'D]

HTH,

Thanks for the reply. The last engine I rebuilt was a while back. I probably didn't have any spec on the clearance and the machine shop bored it to whatever they thought was correct. Are these pretty standard clearances for any engine? I understand the grading system and why they used it, but it illustrates the incredibly small difference is piston diameter to cylinder diameter that they used. I plan to get the pistons from SS, so am I to assume there will be a clearance recommendation with them?

Thanks again.

Mike

 

[husky drvr]

Mike,

I'm not familiar with the pistons from SS. When you order the pistons, ask if they know the specs.

You should try to get in touch with Jan Servaites in Dayton, Ohio (aka Jumpin Jan here on the forum), the resident expert on rebuilding and machining the Rootes engines. He should be able to answer any question you have about your rebuild.

I'm still learning about this new forum. I didn't realize that my stored "signature" isn't showing in my posts.

HTH is Hope This Helps

Have fun,
Don

 

[Mike O'D]

Thanks Don. I didn't pick up on HTH - funny! I'll try to get a hold of Jan for some clarification.

Mike

 

[jumpinjan]

A typical piston-to-wall clearance is no smaller than 0.0020" - 0.0025".
The piston manufacturer should provide some information with the pistons, but if not, a competent machine shop will decide the clearance, since they do this work (fitting new pistons) a lot.
But, please do set the ring gap to what the shop manual says.
Jan

 

[Mike O'D]

Thanks Jan. Well, don't leave us hanging - what gap should we use?

 

[chryslerwagon]

book says .025 ring end gap
I'm currently rebuilding my 1725 and getting more info here-thank you everyone for your posts

 

[Mike O'D]

Thanks everyone for the responses. Opinions wanted (facts would be really great) on this - Visard mod will reduce the compression ratio if nothing else is done to the engine to make up for it. Does the mod more than make up for the reduced compression?

Mike

 

[Bill Blue]

Mike, you have touched on something I have been thinking about for twenty years. Facts as I understand them.
1) Modern gasoline in the USA does not have an adequate octane rating for the stock Alpine.
2) The typical Alpine has to run with retarded spark to avoid spark knock.
3) The Vizard modification lowers the static compression ratio.
4) The Vizard modification improves air flow, which increases dynamic compression ratio.
It seems to me the change in compression would be pretty much a wash. If not, the ignition could be advanced to regain some lost power. If all this is true, there is nothing to be gained from increasing static compression ratio to stock specifications.

Bill

 

[Mike O'D]

Bill,

Thanks for the excellent response. What you are saying makes a lot of sense. If engine power remained about the same, but operation was pushed farther away from knock, it may still be worth it.

Mike

 

[65beam]

Mike, you have touched on something I have been thinking about for twenty years. Facts as I understand them.
1) Modern gasoline in the USA does not have an adequate octane rating for the stock Alpine.
2) The typical Alpine has to run with retarded spark to avoid spark knock.
3) The Vizard modification lowers the static compression ratio.
4) The Vizard modification improves air flow, which increases dynamic compression ratio.
It seems to me the change in compression would be pretty much a wash. If not, the ignition could be advanced to regain some lost power. If all this is true, there is nothing to be gained from increasing static compression ratio to stock specifications.

Bill

Bill,
I have several series 5 manuals that say use 96 octane gas. I don't remember ever seeing anything that high although 92 & 93 are still available in some places.

 

[todd reid]

IIRC the octane rating methodology was revised back in the 70's (??), so we may not be comparing apples to apples. I ran my 1725 on regular for 10+ years without issue, but it is quite possible that worn parts had reduced the compression from where it was when it left the factory. Here in PA, 92/93 premium is readily available - I can't remember visiting a station that didn't have it.

 

[65beam]

IIRC the octane rating methodology was revised back in the 70's (??), so we may not be comparing apples to apples. I ran my 1725 on regular for 10+ years without issue, but it is quite possible that worn parts had reduced the compression from where it was when it left the factory. Here in PA, 92/93 premium is readily available - I can't remember visiting a station that didn't have it.

The entire petroleum industry was different prior to the oil embargo of the early 70's. Crude wasn't traded on the commodity market until the late 80's. I use whatever is available at the time. I use premium in my beams if available. 92 or 93 is a very rare item in stores in my area but our local Speedway does stock multiple grades. A Sunoco branded truck stop about 30 miles east of me has 110 race gas at the pumps. Notice that I said "stores". There are no places that sell gas and have service bays so it's all a matter of fast moving or slow moving inventory. Slow moving inventory doesn't pay the bills so most independent owned C stores in this area now carry 87 only. Everything is 10% ethanol except in areas near surrounding state borders and that product is pulled from those surrounding states.

 

[husky drvr]

IIRC the octane rating methodology was revised back in the 70's (??), so we may not be comparing apples to apples. I ran my 1725 on regular for 10+ years without issue, but it is quite possible that worn parts had reduced the compression from where it was when it left the factory. Here in PA, 92/93 premium is readily available - I can't remember visiting a station that didn't have it.

Todd,

IIRC, the methodology didn't change - the fuel changed. I also think that England used a different methodology than the US for octane ratings when our cars were built. I'm not sure there is a easy comparison, all things considered.

When EPA mandated the phase out of using lead as an anti-knock agent in fuel, the ability to economically maintain the fuel octane levels that TEL (tetra-ethyl-lead) made possible went away. I think I recall in this area, leaded regular fuel was rated at 96 or 97 octane and premium was considered 100 octane. When unleaded fuel for cars with catalytic converters had to be accommodated, many stores converted the premium tanks and pumps to unleaded instead of installing new storage and pumping systems. Leaded regular did stay available until about the early 90's. It was only a couple of years later until the cylinder head in my truck was destroyed due to valve recession because of no lead in the fuel. The use of ethanol as an anti-knock agent and oxygenator in todays fuel leads to a couple of issues for older vehicles that were designed for leaded fuel. The affinity to absorb water, possible corrosion due to the water content, and fuel system materials that were never designed to be compatible with ethanol are reasonably well documented and understood. One thing that is only rarely mentioned is that the BTU content of ethanol is only about half of pure gasoline. A 90-10% mixture of gas and ethanol would deliver a fuel/air ratio about five percent lean by volume as designed into the fuel delivery system which could lead to some drivability issues.

Just some thoughts on today's fuel,

Have fun, Don

 

[Barry]

Actually, both the fuel and the octane rating method changed.

The 94 octane low-lead and 100 octane high-lead gasolines of the late 1960's were based on a test method called the Research Octane Number (RON). There was also the Motor Octane Number (MON) test method which resulted in octane numbers about 10 points lower than the RON numbers for the same gasoline. For marketing reasons, the "Seven Sisters" went with the higher RON numbers.

The Clean Air Act of 1970 changed everything. In order to meet the new exhaust emission standards, Detroit started using catalytic converters which could not tolerate leaded gasoline and gas stations were required to sell unleaded gas for new cars. By the mid-1970's, Detroit had dropped compression ratios (to meet NOX emissions requirements) to the point that new cars had no need for high octane gasoline.

In the early 1970's, the U.S. government required that posted / advertised octane ratings for auto gasoline had to be based on the average of the RON and MON values (R+M/2). Gasoline which had been 100 RON octane (and about 90 MON octane) became about 95 R+M/2 octane.

The bottom line is that the anti-knock characteristics of modern 87 / 90 / 93 R+M/2 octane gasolines are roughly equal to 92 / 95 / 98 RON octane gasolines from the late 1960's.

 

[65beam]

Todd,

IIRC, the methodology didn't change - the fuel changed. I also think that England used a different methodology than the US for octane ratings when our cars were built. I'm not sure there is a easy comparison, all things considered.

When EPA mandated the phase out of using lead as an anti-knock agent in fuel, the ability to economically maintain the fuel octane levels that TEL (tetra-ethyl-lead) made possible went away. I think I recall in this area, leaded regular fuel was rated at 96 or 97 octane and premium was considered 100 octane. When unleaded fuel for cars with catalytic converters had to be accommodated, many stores converted the premium tanks and pumps to unleaded instead of installing new storage and pumping systems. Leaded regular did stay available until about the early 90's. It was only a couple of years later until the cylinder head in my truck was destroyed due to valve recession because of no lead in the fuel. The use of ethanol as an anti-knock agent and oxygenator in todays fuel leads to a couple of issues for older vehicles that were designed for leaded fuel. The affinity to absorb water, possible corrosion due to the water content, and fuel system materials that were never designed to be compatible with ethanol are reasonably well documented and understood. One thing that is only rarely mentioned is that the BTU content of ethanol is only about half of pure gasoline. A 90-10% mixture of gas and ethanol would deliver a fuel/air ratio about five percent lean by volume as designed into the fuel delivery system which could lead to some drivability issues.

Just some thoughts on today's fuel,

Have fun, Don

Octane rating is a number that indicates the ignitability of the gasoline/ air mixture under compression. A 92 octane will withstand higher compression before igniting. You find that at high altitudes such as Colorado you'll find the use of 85 octane due to the atmospheric conditions. The Clean Air Act of 1970 started the initial reduction of lead in gas. The use of unleaded started in late 1974 with the use of cat convertors which required reduced amounts of lead even though both leaded and unleaded were available. Many regulations for the refiners were postponed until 1979 due to refining capacity of the refinery. I know of many folks that knocked the honey comb out of their cat convertor and continued to use leaded due to the cost difference.. It was possible to go to an auto parts store and buy a section of pipe made to fit your car in order to replace the cat convertor. The nozzle diameter for unleaded was smaller than the one for leaded gas and cars designed to run on unleaded had a smaller opening in the fuel filler so every chain store started selling a plastic funnel made to fit the unleaded fuel filler and allow you to pump leaded gas. Leaded fuel was totally banned in 1996. The water problem with ethanol was quickly recognized and all retailers were given a time frame to install monitoring systems and upgrade their tanks. One of the primary reasons being the water issue . Water in E10 will form small balls that can plug filters. I think it was 1998 that we were mandated not to sell to any store with out a monitor or the upgrades. Mom and pop stores were out of the gas business at that time. Many states such as Ohio gave excise tax breaks to further the use of E10. It's easy to understand why old school technology of engines went away. The changes made to diesel is another story

 

[Tim R]

In the U.K. Ethanol in petrol has caused a number of classic car fires. The percentage is soon to increase from 5% (E5) to 10% (E10) and the problems will undoubtedly increase too. Apart from the water issue that 65beam mentions the problem with old cars tends to be that it makes rubber hoses, seals and gaskets soften and swell and it inundates plastic (for example making plastic carb floats sink). I am restoring an Alpine at the moment and trying to make it as Ethanol proof as possible but it is hard.
So far I have treated the fuel tanks and metal pipes with POR15 and replaced the rubber pipes with R9 Ethanol proof hose. The new Weber carb that I have has a similar float to one that previously sank on me and I don't know if this is the later 'ethanol proof' one or not and I also don't know how resilient the diaphragm in the fuel pump will be (I have electric pumps in our other two Alpines).

Unfortunately a handful of virtue signalling Green Warriors have massive influence over the Government and even though a lot of their claims simply don't add up when they are subjected to scrutiny National policy gets changed to follow their agenda. Growing food to turn into a poorly performing fuel is wrong on so many levels.

Tim R

 

[Mike O'D]

Great information - thanks guys!

Mike

 

[67BEAMR]

book says .025 ring end gap
I'm currently rebuilding my 1725 and getting more info here-thank you everyone for your posts

Thornton rings of England disagrees sharing instead a ring gap of .0016 for 1st ring and .0025 for 2nd and 3rd oil thrust rings.