The elusive 224/3.7 MerCruiser banger

I have often wondered how the timing sets for line bored engines differ from the standard ones. Is the chain actually shorter, the sprockets slightly larger, or the rollers just a bit bigger in diameter?

Another modification that is made in max effort engines is the cam bores offset and bored oversize for roller bearings. This has been done on the Mercruiser but I don't know for whom.

 

It's a combination of all those components being made/machined for a shorter center to center dimension.

 

I'm still stuck on this block growing and tightening up the chain. My plan was to use a 460 chain. I measured my block cam to crank at 6.082. It was listed earlier in the thread that 460 is 6.078, so I thought 460 would work as is. Wrong, I tried three different sets, all were loose. I was going to just drill out one of the three holes to hold a standard Ford pin like most Fords use, cut the cam off, drill and tap for a stock type 460 set up. But the I rolled the cam over and there was the damn key way. Still may do it with a 3/8 bolt that will allow me to run my fuel pump off the end of the cam. The other way would be to broach the keyway into the stock 460 gear and drill the three holes. All doable. I am using 9 key lower gear old SVO timing set.

 

I have never heard of offsetting the cam for roller cam bearings, or for any other propose. Maybe just me being stuck in Alaska for the last 50 years. I have put roller bearings in a few 460's and know they didn't want a lot of press on the bearings. Again I would be afraid of putting roller bearings in the Mercruiser for fear they would fall out when hot. I know its been done before, but I don't think I will do it.
Just a pic of more mock up.

 

Hey Flatrod, many Rodeck and other brand aluminum race blocks use roller cam bearings in them. One feature you may not be aware of, being stuck in Alaska and all, is they have a narrow slot machined into the block in front of and behind each roller bearing to install a spirolock to prevent forward and rearward movement of the bearings, because they do have a very light interference press on them.
Also, another easy science experiment you can perform to determine the Mercruiser thermal expansion rate is to set the block outside for about an hour to freeze in the Alaska winter air. Bring it inside and measure the cam/crank centerline. Then set the block in front of a Kerosene heater for a while to let it get to about 180° to 200° to simulate operating temps and measure this distance again. With that amount of temp variation, you should easily be able to discern the expected expansion of the Merc block to validate your concerns.

 

I have done work on one Rodeck and two Donovan's in my years. But have worked on many KB blocks. I forgot they use roll pins to hold the bearings in place, and most I have seen use 460 cam bearings. Never seen a KB with roller bearings.
Its 2 below this morning. maybe throw the block out and see how bad in moves!

 

Most of us in the past may have heated a crank gear or timing gear to expand it for easier installation. So if the ID gets larger with heating, so does the rest of the gear and chain. All the internal engine components get a constant soaking of engine oil that is typically between 250 to 260 degrees. I'm sure the engineers took that into consideration when designing these engine blocks. I'll bet at operating temps, the chain slop is probably tighter than when the engine is cold.

 

Didn't know if there was any hard data ever posted regarding the cam to crank C/L dimensions between the 429/460 and the 3.7L Merc. Here is what i've found:
From Cloyes website:
429/460---6.078", stock center to center timing set
429/460---6.073", -.005" shorter than stock timing set
429/460---6.068", -.010" shorter than stock timing set

3.7L Mercruiser----6.055", center to center measured on stock block

 

That's useful information for those of us that are into max builds. I wonder if there is a way that we could consolidate dimensions like this into a chart and insert it at the beginning of the thread. That way anyone starting out to build up a 3.7L wouldn't have to scour through the whole thread to find it.

If @tjm73 would be willing, folks that come up with various info could submit it to him and he could add it to the original post via an edit. I envision something like an excel spread sheet converted to a .pdf file. (HAMB does not accept .xls files) It could be replaced with an updated version at any time.

I would be glad to develop this, but I think it needs to be at the very beginning, not just stuck in the middle somewhere.
Whutcha think?

 

I agree! I have spent the last couple of days going back to the beginning and re-reading this entire thread to get all the info back fresh in my mind.

 

@Flatrod17,
Did you tell us what water pump that is? I like that it is centered over the crank leaving the end of the cam available for whatever.

 

Its the same pump most are using here. I could not find the one Dennis G has or the other with the long ear sticking up. My pump is Gates 42221 for a 77-79 Toyota Corolla Starlet 3kc 1.2L engine. I have positioned it so the water outlet and the merc inlet are close and the hose connection is straight out. My back plate is 1/2 thick and will have to be remade to support the pump there. Its not quite centered like I wanted it. I wanted to use a fan bolted to the pump and wanted it centered in the rad. The pulley flange is drilled 6mm but is the same pattern as Ford. I think Dennis G did not block off the stock Merc cover, but I want to block it off so water doesn't run back down to the old seal area.
So with all that said I'm thinking about this. Its a old marine pump its off the front cover of a nailhead I have laying around. Looks like it could be a simple hook up.

 

Making an 8620 billet roller cam blank for a friends 153 Chevy II four banger.....Some for the Mercruiser are next!

 

Those round lobes won't give much lift, even with 1.8 rockers

 

It's a round lobe blank, the cam grinder will finish them. I think hydraulic roller cams for the Merc would be something of interest to some on here....

 

Will your cores have dist gears?

 

Yes, if the guy that can cut them on them will still do it.

 

I would be interested in one. My project is dead for the next 6 weeks, waiting on pistons to be made.
Please let us know how these are coming along.

 

Ok, it may be a while till I get the current project finished. I'll also have to source material for Mercruiser blanks as well.

 

Yep, keep us informed as to progress on the cam blanks. A hydraulic roller with a distributor gear would make my day.

 

I'm shooting for a hydraulic roller. I've got 2 engines to use for mockups and getting all the data I need.

 

There was a dimensioned drawing earlier in this thread. The lobe spacing for a roller is somewhat different than a flat tappet. Between that, and your mockup engines, you should be able to get some very usable specs.

 

I remember seeing it. I'll confirm the dimensions once I get the block in the mill and 3D model a cam as well in Solidworks.

 

Hopefully someone has a better idea to prove the following wrong; if using a roller cam in the 3.7 one of two things must be done. With either method, adding a roller cam requires starting with a bare block to keep the machining decree out of the block. The 1st option is, if using a tie bar type roller lifter, to remove the side cover mounting bosses. There then needs to be a different mounting method for the side cover installed. The 2nd option would be to use keyed lifters. If using those, the block lifter bores must be broached to allow for the keyed lifters.

 

Beck, I'm going to be using the best of both worlds approach, do a hydraulic roller that uses the old 5.0 Mustang style dogbone hold downs and allows the side cover bosses to stay intact.
At the least, a drill and tap operation may be needed to fasten the dog bone. Just realize that upgrading to a roller cam, either solid or hydraulic probably needs to be pre-planned and not an afterthought because it may require some internal mods to the block. One thing to consider is that most people that have run solid roller cams also likely bored the cam tunnels for roller cam bearings. I don't think I would trust installing one on the bare cam bores with the greatly increased spring pressures required for solid rollers. A hydraulic roller not to much of an issue though because they only require barely more spring pressure than a hydraulic flat tappet cam, comparatively speaking.

 

You could cut the distributor gear off of an old mercruiser camshaft, bore it, slip it onto a "round lobe" prepared for the inside of the camshaft distributor gear and braze it in place. the lobes in front of the distributor gear would have to be replaced as the cam gear was.

The stock cam has lots of metal available for regrinding and makes a good blank. That is about all it is good for anyway.

 

I used a waterpump from an early 70's corolla. It looks odd as it is upside down to make the pump outlet match the inlet of the block.

I did not have to keep water out of the chamber for the waterpump because I used a welch plug to keep water away from the camshaft. I had to cut off the camshaft nose so i could use a welch plug. The point of doing it this way was to eliminate the problem of cam shaft wear and leaking at the seals.

Otherwise, the mercruiser waterpump is ok. Electrical pumps are of course way easier to do and for competition which lasts only seconds can be shut off for that freeing up more power.

You can print the full size pattern of the 1/4" or 3/8" backing plate that makes it all fit. I posted the pattern for it here long ago. Given the availability of different lengths of junkyard pullies , the waterpump pulley can line up nicely with a drive pulley bolted onto the front of a dampener.


[sorry to be so slow to reply as I've been offline for several weeks due to an ice storm.]

 

I'm still concentrated on the leaking gasket problem. A dry deck would get around the problem but there would be no provision for"steam holes". I do not know how easy it would be to purge the air from the block then, but if not drained away, the air would be exactly where you can't have it in the top of the block.

Other than that solution, a sealant with elasticity and more width of the lifter gallery ledge may be needed, especially if an elastic fiber (silk? sisal? hemp? )is in it along the critical sealing area. Glass is quite elastic but is hard to compress.

 

Something that most all NASCAR teams do whether they are Chevy, Dodge or Ford is drill a series of small holes vertically between the siamese cylinders to allow water to travel from the lifter valley side of the water jacket to the other to eliminate steam pockets and this problem. The holes aren't very large in diameter and are usually a total of 3 or 4 holes in a vertical pattern about a half an inch apart or more, depending on the space you have to work with.

 

I want to make sure that I have this right. Matching holes would be drilled in the deck, head gasket and the head. Or with an open deck engine, through the gasket and head.